Category Archives: LED

Citizen COB lineup

Citizen COB LEDs generation 6 – What is new?

Citizen have released generation 6 from their successful series of Citizen COB LEDs. In this post I’ll go briefly through, what is new and what advantages these COBs have compared to previous generations.

There are five main points at generation 6 from Citizen:

1. Performance increase

Performance will up to 7% depending on CRI of LEDs. There will be also slight decrease on forward voltage, which increases lm/W efficacy on LEDs.

2. MacAdam 2-step option

MacAdam 2-step binning will be an option in new generation. Although we have had very tight 3-step binning already, there is now option to order also 2-step versions of COBs. So if you desire to have 2-step SDCM COBs in your products, we have now solution for that.

3.Thermal resistance decrease

Thermal resistance is further decreased from generation 5. Decrease from generation 5 is 5% and from generation 4 even 38,5%. This allows you to minimize your need for heat dissipation. Another option is that you can create new, bigger lumen categories with your existing products.

Thermal Resistance

On the left a heat sink needed for COB Gen 4 LED. On the middle heat sink needed for gen 5 LED. On the right, heat sink needed for COB gen 6 LED. The power of the LED is same in every case.

4. Increase of maximum Tc

Maximum Tc-temperature has been set to 120 degC. Allowable Tc-temperature will rise from 105 degC to 120 degC. This will help you to maximize light output from your design, so you can use smaller heat sinks to get more light.

5. Increase of maximum Tj

You will be allowed to have higher Tj-temperature than in previous generations, so maximum Tj-temperature will be now 150 degC. This will give you wider LED driving options especially with bigger COB packages.

Citizen COB LEDs continue to increase their performance and offer amazing coverage for lumen packages. Packages range from under 100 lumens up to 60 000 lumens from single light source. If you haven’t yet tried Citizen COB LEDs, now it is good time to learn why Citizen has been top player in the industry for so long time.

You can download the whole catalogue, datasheets and simulator tool for Generation 6 COBs from our website.

Download Catalogue, Gen 6 Datasheets and Simulator Now

Different Dimming Types for LED Lighting

You can use several different dimming options to dim LED Lighting. What are the possibilities and what dimming should you look from a LED driver? I’m going to answer these questions in this blog post by going through the different systems.

The goal is to give you the basic understanding of the dimming methods available at moment.

I am grouping the dimming methods in two main groups: analogue and digital.

When you want to control lighting, you have to know some basic issues of your lighting fixtures:

  • Are your fixtures dimmable? If yes, what is the dimming method which works together with your fixtures
  • If your fixtures are non-dimmable, then you can only have on/off – function.

Analogue

Analogue dimming covers all dimming systems that don’t transform the dimming signal into bits and controls the lighting in analogue manner.

Phase dimming

Phase dimming systems dim the lights by altering the supply voltage.

Leading & trailing edge dimming

Before LEDs, we used to dim halogen lamps with wall dimmers.  We can still use these kinds of dimmers.  But dimmer, driver and LED-module must be compatible with each other.

This type of control is accomplished without any need for an additional control wire. It involves connecting a dimmer in series between one of the mains wire and the equipment.

The dimmer cuts part of the mains voltage sinusoidal waveform to a greater or lesser extent in order to dim luminous flux even from 1% to 100%  (this value depends on dimmer and driver).

Depending on how the driver makes the mains voltage cut, it is possible to distinguish between two types of dimming:

Leading-edge dimming

Leading-edge dimming

Trailing edge dimming

Trailing edge dimming

Leading-edge dimming:

Dimming cut-off in the wave on its ascending side, from the beginning (phase cut-off at ignition). This is traditionally used in halogen lamps supplied through electromagnetic transformers.

Trailing-edge dimming:

Dimming by cut-off in the wave on its descending side, from the end cutting backwards (phase cut-off at switch off).  And this way of dimming causes less interferences than leading-edge dimming.

There are dimmers and equipment that support both types of dimming, and others that support only one type.

Leading & Trailing-edge dimming LC

Leading & Trailing-edge dimming LC

Leading-edge dimming L

Leading-edge dimming L

Trailing-edge dimming  C

Trailing-edge dimming  C

1-10V regulation

The 1-10V system enables dimming of the luminous flux from around 1…10% to 100%. This is done by sending an analogue signal to the equipment over an additional, two-wire control line. These control wires have positive and negative polarities respectively and that must be kept in mind when wiring up the system.

The analogue signal has a direct voltage value of 1V to 10V. 1V or short-circuiting the fixture’s input control gives the minimum light level. While 10V or leaving the input control circuit open gives out the maximum light level.

International standard, IEC 60929, defines the regulation curve. The regulation curve represents the relationship between the control line voltage and the luminous flux. It reflects a practically linear relationship in the range of 3V to 10V.

To get a response adapted to that of the human eye it is possible to use logarithmically controlled potentiometers.

Regulation curve by IEC 60929

Regulation curve by IEC 60929

These in light fixtures generate power control with 1-10V dimming.  Driver supplies a current to the controller through equipment control terminals. The controller current must be from 10µA to 2mA. The maximum control line current is obtained with a voltage of 1V and the minimum with a voltage of 10V.

This dimming system is unidirectional, i.e. the information flows in one direction, from the controller to the light fixture. The latter generates no feedback to control. This means that this system can’t be controlled by a software. Groups have to be created by wiring. This system can be integrated into building control systems.

The voltage drop in the control line wiring limits its length. Therefore, the maximum distance is limited by the number of control gears connected. The latter establishes the current per line and the cable diameter used.

Touch Control Push Button  (analogue but can be connected to digital systems)

Touch Control is a system that enables the simple and economic dimming of luminous flux. It uses the mains voltage as a control signal, applying it with a standard push button on a control line, without any need for specific controllers.
The Touch Control system enables you to carry out the basic functions of a regulation system with a power-free pushbutton. Depending on how long the button is pressed it is possible to switch the light on or off or dim it. Switching the light on or off is done by short, sharp pressing or “click”. If the button is pressed for a long time it is possible to dim the luminous flux between the maximum and minimum levels alternately.

Touch Dimming

Touch Dimming

This is a unidirectional interface, i.e. information flows in one direction. The equipment does not generate any type of feedback, so it can’t be controlled with a software. Groups have to be created by wiring. This system cannot be integrated into building control systems.

The length of the wiring and the number of equipment that can be connected, are theoretically unlimited. But in, asynchronism may occur during switching on and dimming, at distances longer than 25 meters, and with a larger number of fixtures connected.
Owing to its characteristics, the use of this dimming method is recommended for individual offices, small meeting rooms or bedrooms, landings and small spaces in general.

Digital

Digital dimming covers all dimming systems that transform the dimming signal into bits and controls the lighting in digital format.

DALI Regulation (digital)

As revealed by the meaning of its acronym, Digital Addressable Lighting Interface, DALI is a digital and addressable communication interface for lighting systems.

This is an international standard system in accordance with IEC 62386, which ensures compatibility and interchangeabil­ity between different manufacturers’ equipment marked with the following logo: DALI controller

DALI-logo

DALI-logo

It is a bi-directional dimming interface with a master-slave structure. The information flows from a controller, which operates as the master, to the control gears that only operate as slaves. The latter carries out the orders or responds to the information requests received.

Digital signals are transmitted over a bus or two-wire control wire. These control wires can be negatively and positively polarized, though the majority control gears are designed polarity free to make connection indifferent.

DALI Dimming

DALI Dimming

You don’t need especially shielded cables. It is possible to wire the power line and DALI bus together with a standard five-wire cable.

Unlike other systems, you don’t need to create wiring groups. Therefore all the pieces of fixtures are connected in parallel to the bus. Without bearing in mind the grouping of these, simply avoiding a closed ring or loop topology.

You don’t require mechanical relays to switch the lighting on or off, given that this is done orders sent along the control line. You don’t need are bus termination resistors either.

Consequently, the DALI interfaces offer wiring simplicity in addition to great flexibility when it comes to designing the lighting installation.

The maximum voltage drop along the control line must not exceed 2V with the maximum bus current of 250mA. Therefore, the maximum wiring distance allowed depends on the cable cross-section, but it must never exceed 300m in any case.

Configuring

After wiring, the DALI lighting system is configured with the software. You can create up to 16 different scenarios, addressing the equipment individually up to a maximum of 64 addresses.  This can be made with groups up to a maximum of 16, or simultaneously by means of a “broadcast” order. You can change the configuration at any time without any need for re-wiring.

The DALI system has a logarithmic regulation curve adjusted to human eye sensitivity, defined in the international standard, IEC 62386. The possible regulation range is set at from 0.1% to 100%. The driver manufacturer determines the minimum.

DALI Regulation Curve by IEC 62386

DALI Regulation Curve by IEC 62386

With the software, you can change the “fade rate”. “Fade rate”is the time needed to go from one light level to another(fade time) and the speed of the change.

The DALI system lies in the fringe between the complex and costly but powerful ones; control systems for buildings that offer total functionality and the most simple and econom­ic regulation systems, for example, the 1-10V one.

You can use this interface in simple applications indepen­dently, to control a luminaire or a small room. You can also use it in high-level applications such as being integrated by gateways into building smart control systems.

These are the most common systems you can use to dim LED. There are a lot of different dimming systems for different driver manufacturers. I can’t cover all of those in a single blog post. I will be writing a different post about wireless dimming options.

If you have anything you would like to know, you can always contact me taru.oksala@light.fi .

Sources: ELT

FAQ: aLED Modules

Q:You have the driving current 700mA written in the datasheet of your LED module.  Can I use smaller driving current?

A:Yes, you can use smaller current. The current value 700mA mentioned in the module’s data sheet is so-called nominal/typical value that corresponds to the value Citizen announces for voltage and luminous flux (lumens) of the diode used in that LED module.

The minimum current is defined by the diode datasheet and in our 700mA modules the minimum current is 70mA. But you can also use the larger current. The maximum current is 1190mA. Please notice that you have to take care of cooling of the module in case that you use the maximum current. The warmer the module, the lower the lumen output and the shorter the lifetime.

CALC-0814 Absolute Maximum Ratings Found From the Datasheet

CALC-0814 Absolute Maximum Ratings Found From the Datasheet

Q: What is the IP classification of your aLED modules?

A: It is basically IP00, because if our LED arrays are not placed inside the luminaire, they are subject to dust and moisture. So if you need IP classification for your luminaire, please ensure that the luminaire casing has the desired IP classification.

Q: Ok, your aLED modules are classified as IP00, can they then be potted or protected from dust or moisture with some special coating?

A: Basically if you want to cover them with some coating or even pot them, you have to always contact the supplier of that coating or potting material to find out how it affects the LED components. Usually LED manufacturer gives some warranty for their products but this warranty applies only under certain pre-specified constraints or conditions.

Additionally, using coating may alter, and probably does so, optics of the LED components from the characteristics announced in the datasheet of the LED component manufacturer.

So basically you can use potting or special coating, but you should always check how the process affects the module.

Q: How the driving current affects the lifetime of LED module?

A: The lifetime estimations curves, lifetime hours versus temperature TC, are informed for the LED modules at their maximum rated current. That means that maximum condition is used and then lifetime hours are announced at different TC temperatures. The TC point is found in every LED module and is usually located near the soldering terminal, anode or cathode, of the LED diode located near the center of the module.

CALC-0814 Lifetime Estimation curves

CALC-0814 Lifetime Estimation curves

Higher current means higher Tc point temperature and therefore it means shorter lifetime. On the other hand, lower driving current means lower Tc point temperature and therefore longer lifetime.

Q: Are your modules MacAdam 3-step compliant?

A: Our aLED modules follow color consistency in MacAdam 3-step. This means that from production batch to production batch color coordinate values stay within the MacAdam 3-step ellipse. This means that our modules are MacAdam 3-step compliant.

Depending on the CCT, variation in Kelvins is different for MacAdam 3-step, being ±65K for 2700K and ±140K for 4000K.

For 5000K and 6500K our LED modules are only within ANSI binning, not within MacAdam 3-step.

Q: How many aLED modules  you can drive with one 50W/90W 700mA driver?

A: It depends on the module, of course. For the sake of an example lets look at CALC0814-M17W1.

First of all, as you can see from the module’s datasheet, the power is 700mAx24.16V = 16.9W. This is power when the module is driven with 700mA typical current. If you use one 90W driver, you can drive 5 module in series connection.

Let’s do still check calculation. As given by the module’s datasheet, the maximum voltage of the module is 26.4V if all LED diodes are at maximum value of voltage binning range. This is unlikely, but should be checked anyway. Total voltage of 5 modules in series is 5×26.4V = 132V. In our example case the LED driver’s maximum output voltage is 129V. However, the case that all 40 diodes in series connection would have 3.3V (maximum voltage of voltage binning range) is very unlikely. With typical rated value of 3.02V given in the diode’s datasheet, total voltage of 5 modules in series is 40×3.02V = 120.8V, which is within driver’s output voltage range.

So 4 modules is definitely ok. Probably you could drive five, but then we would need to check that they all are from the typical binning.

If you use 50W driver, you can safely drive only 2 arrays in series connection. In our example case the LED driver’s maximum output voltage is 72V. If you drive 3 arrays in series, even the typical voltage is 3×24.16V = 72.48V, which is too much for the driver.

Q: How do you calculate aLED module’s total voltage and total current.

A: We use the information of the diode and the information how many diodes there are in series and how many in parallel.

Circuit Schematics for CALC0814

Circuit Schematics for CALC0814

Let’s take CALC0814-M17W1 as an example. Numbers ‘08’ and ‘14’ refer to electrical configuration of the diodes in the module. First number, ‘08’, refers to how many LED diodes are in series between the + and – terminal of the array.  Second number, ‘14’, refers to how many LED diodes are parallel in one LED chain. In this example, there are 8 pcs of LED chains in series and 14 LED diodes connected in parallel in each LED chain.

Typical value for the diode is 50mA and therefore there is 700mA going through each chain (14x50mA). That gives the total current of the module. With this typical current of 50mA, the diode forward voltage is 3.02mA and there are 8 LED chain in series in this module. This means the typical total voltage of the module is 24.16V (8×3.02V).

Q: aLED modules have quick connectors. Can I use soldered wires instead of quick connectors?

A: Yes, you can. If there are no separate solder pads for soldering wires, you can use quick connector solder pads but in this case the connector is not assembled in the assembly process. In some aLED modules both options are possible simultaneously.

Please note, that with different connectors, the delivery time might be little longer.

If you have some other questions, that were not found in this list, please feel free to ask me. I will answer to you directly and add the general questions to this FAQ later.

Tero Nurmi
Product Manager
aLED Modules
tero.nurmi@light.fi

CIE 1960 Chromaticity Diagram

Why the Same Color Temperatures Look Different?

We see more and more light sources that supposed to be exactly the same color temperature, but actually appear different to human eye. So why the same color temperatures look different?

When people talk about color temperature, they are usually talking about correlated color temperature instead (CCT). There is a difference between these two.

Color temperature (CT)

Color temperature (CT) defines what is the exact spot of the light source is on the planckian locus line.

This line in pictured in the below image as the black line in the middle.

So if there are two light sources, that have a color temperature of 4000K, they both look exactly the same as they both are on the same spot.

Correlated color temperature (CCT)

Correlated color temperature is used when the light source is off from the planckian locus. If CT defines the exact point on locus, then CCT defines the perpendicular line which runs directly through that exact point. So if a light source is off from the locus, then CCT is the CT point which is closest on the locust.

So for example if a light source has a CCT of 4000K, that means that it can be on any point on the line that runs through the 4000K point on the locus.

You can see these lines on the image.

Typically a light sources color temperature is announced as CCT. So if it is said that two light sources have a CCT of 4000K, this means that they are on the same line that runs through the 4000K spot, but may, in fact, look totally different.

CIE 1960 Chromaticity Diagram

CIE 1960 Chromaticity Diagram (image source)

Chromaticity coordinates

Usually, light source’s chromaticity is defined in diagram as chromaticity coordinates. In this diagram, you can’t determine that CCT is the shortest distance to the locus. You can see the chromaticity diagram in the image below.

(x, y) Chromaticity Diagram

(x, y) Chromaticity Diagram (image source)

So when you have three luminaires which have the same 4000K CCT, you can have three totally different colored lights.

If the light has a greenish white light, that will mean that the chromaticity coordinate is above the planckian locus.

If the light has a purple tone, then chromaticity coordinates are below the locus.

If the light is normal white light, then the chromaticity coordinates are on the locus or at least very close to it.

So please remember that staring at the CCT doesn’t always tell you everything. If you use two different light sources with the same CCT, you should always check the coordinates and see if these two are actually the same color.

 

 

How Lifetime Affects the Energy Savings of a Luminaire

Generally, when selecting LED luminaires, the attention is drawn to energy consumption. Efficacy, therefore, the power consumption, is the most important selection criterion. But do you pay attention to the lifetime of the luminaire? What happens if the better efficacy luminaire has shorter lifetime? This means that you may have to renew the luminaires much quicker. This adds expenses and eats off the savings from the electricity bill.

Lifetime of LED Light Source

Compared to traditional light sources, the lifetime of an LED light source is long. When a traditional incandescent bulb or a fluorescent tube runs out of its lifetime, it can’t be used anymore. It either won’t produce light or starts to flicker. LED only loses some of its brightness and is, at least in theory, eternal.

This is the reason why the lifetime of LED light sources is measured in a different fashion compared to the traditional. The lifetime of a traditional light source means literally lifetime. LED’s lifetime tells that at what point the amount of light drops below the desired value.

The terms for LED Lifetime:

  • L70, L80, LXX = How much of the original lumens are still available. For example L70 means that the light source still produces 70% of the original lumens. So if the light source produced 1000lm at the beginning, this has dropped to 700lm.
  • B50, B60, BXX = How many light sources are below the given lumen value. So e.g. B50 means that 50% of the light sources don’t produce the desired amount of lumens anymore.

Typically the lifetime is given as a combination of these two. For example L70B50: 60.000h means that after 60.000 operational hours 50% of the light sources still produces at least 70% of original lumens.

aLED Moduulin elinikäennuste

Lifetime estimate of aLED module

The lifetime can also be given using only the L-value. For example L70: 60.000h. Then the manufacturer doesn’t actually promise how many of the luminaires are still over 70% after 60.000h.

Taking Lifetime into Account When Selecting Luminaires

Let’s assume that you are lighting a space that has 1000 luminaires. For example a shop. You have narrowed your luminaire choices down to two: Option A and Option B. Currently the space has fluorescent lighting and more specifically 58W T8 luminaires, which produce roughly 4000 lumens each. Here are your options:

  • Option A
    • Luminous Flux :4000 lumens
    • Efficacy 150 lm/W
    • Power: 26.7 W
    • Lifetime L70B50: 50 000 hours
    • Price 120€/Luminaire
  • Option B
    • Luminous Flux :4000 lumens
    • Efficacy 130 lm/W
    • Power: 30.8 W
    • Lifetime L70B50: 90 000 hours
    • Price 120€/luminaire

It’s easy to choose option A. The power consumption is lower as the power is around 4 watts smaller. For example in your 1000 luminaire space this means 4kW and a significant savings in your electricity bill.

When you know the daily operational hours, you can calculate the annual electricity consumption and compare that to the old solution. For the sake of an example, let’s assume that your shop is open for 14 hours a day. When you add the time for cleaning etc., your daily operational hours are 16. At least in this example.

This way you get the following math:

  • Annual operational hours: 16h*365= 5840 h/year
  • Price of electricity: 0.1€/kWh
  • Traditional (58W Fluorescent)
    • Annual electricity consumption: 1000*58W*5840h=338720000Wh= 338720kWh
    • Electricity bill: 338720*0.1=33 872.00€
  • Option A:
    • Annual electricity consumption: 1000*26.7W*5840h=155928000Wh=155928kWh
    • Electricity bill: 155928*0.1= 15 592.80€
  • Option B
    • Annual electricity consumption: 1000*30.8W*5840h=179872000Wh=179872kWh
    • Electricity bill: 179872*0.1=17 987.20€

 

Both LED options drop the electricity bill down to half of the old solution, saving you a lot of money. Option A saves a little bit more, thanks to the better efficacy and lower power consumption.

In short term, option A would be the better solution. As it saves more per year. Option A saves annually around 2.4k€ more than Option B.

However, it is very rare that investment this size is made with a one, two or even five years scope. That’s why we should do the math for a longer period.

When we take the lifetime into account, the situation changes a little.

Let’s first calculate the lifetime in your application. When the daily operational hours are 16, the annual operational time is 5840h, as calculated above.

With this, we can transform the lifetime into a more understandable form:

  • Option A:
    • 50 000h/5840h=8.6 years
  • Option B:
    • 90 000h/5840h=15.4 years

So you would have to change the option A after 8 years while the option B can still light your space for 7 more years (15 in total).

When we look at the total savings caused by the luminaires, the numbers look like this:

Savings in electricity bill after luminaire change

Savings in electricity bill after luminaire change

Lifetime (a) Option A Option B
1  17 582.29 €  14 447.26 €
3  52 746.88 €  43 341.78 €
5  87 911.47 €  72 236.31 €
10  55 822.93 €  144 472.62 €
15  143 734.40 €  216 708.92 €
20  111 645.87 €  168 945.23 €

As you can see from the calculations and the chart above, the option A is better in the short term. But when you look for a long term savings, the option B’s longer lifetime kicks in before the investment reaches 10 years. You will have to replace the option A almost twice as often as option B.

So when you look at the investment in a long-term, the lifetime becomes very important.

When choosing luminaires, you should focus your attencion to both: efficacy and lifetime.  The more expensive the luminaire and the investment is, the more important the lifetime is.

How to Choose Constant Current LED Driver for your Application [Infographic]

The selection of Constant Current driver is not always that simple, Esko wrote a post about it some time ago. You can read that here.

Below you can find an infographic about the same topic. If you like it, feel free to share.

How To Choose Constant Current Driver [Infograpgh]

How To Choose Constant Current Driver [Infographic]

Here is a link to our Lightbuilder.

Flicker in lighting

We get a lot of questions regarding flicker. People are asking what it is and what causes it. I decided to to some research and write a post about the topic. I have very little technical understanding and therefore I try to explain this in simple manner.

What is Flicker

You all know the effect when it is strong enough. Lights go out and on again in very short breaks. This used to be the problem of fluorescent tubes and at least I have learned that this is the time to change the lamp.

Flicker refers to quick and repeated changes in light intensity, which makes the light seem unsteady and broken. This effect is caused by variations in supply voltage or in the power line voltage.

These changes can be caused by dimming or for example by welding machines using high current. Usually voltage changes are quite small and don’t cause any harm to luminaires. However, even small changes can cause flicker and have an effect for people working in offices, schools etc.

Can you see the flicker

It depends. Human eye can see the flashing of the lights up to about 50 to 60 flashes/second (50Hz-60Hz), most sensitive frequency area for human eye is the range from 10Hz to 25Hz. When the frequency is higher that 60Hz most people can’t detect the flicker anymore. Some people have been known to see the flicker up to 100Hz.

In fact, fluorescent lights using magnetic ballasts have a flicker around 100-120Hz, which most people can’t see. This is because it is powered by ballasts with a frequency of 50Hz (60Hz in the US) and lamps flicker with the double frequency. When there is a problem with fluorescent lamp or with the ballast the flicker frequency drops below 100Hz (generally to the ballasts’ frequency) and it becomes visible to human eye.

Flicker from 100Hz to 500Hz can cause a stroboscopic effects, which means that you see objects in motion as series of still images. These kinds of lights are used in discos, but can be extremely dangerous in other environments.

When the flicker reaches a frequency around 2 kilohertz, we can no longer detect it at all.

You can see the flickering in higher frequencies for example with a camera. Although this depends little on the device. The better cameras don’t necessarily show any flicker.

Flicker seen with camera

Flicker seen with camera

Does it harm you?

So this is the big question. Flickering lights have been know to effect headaches, eye strain and fatigue. In Some countries there are laws regulating the maximum flicker in certain environments. For example in Russia there are regulations for schools, offices etc.

Some countries are starting to realize these health problems and have started to regulate the maximum flicker in luminaires.

Measuring Flicker

There is no standard for measuring flicker at least not at the moment. The Illuminating Engineering Society (IES) has developed two metrics to be used to measure flicker: Flicker percent and flicker index.

MF250N Flicker meter

MF250N Flicker meter

Flicker Percent

Flicker percent is the most commonly used metric to measure flicker. This metric tells how big difference there is in one flicker cycle. So it tells that how much does the amount of light drop from the maximum. The 100% flicker means that the light goes completely off at some point and 0% flicker means completely steady light.

For example Russian standards regulate that the flicker of a luminaire must not be over 20% and in some environments the flicker must be 0%.

So Flicker percent is calculated(from the below picture): (A-B)/(A+B)x100%

Flicker Index

Waveform

Flicker index

Flicker index is a little bit more hard to explain. The index has a value between 0 and 1. One being the maximum and zero the minimum.

Index takes the average lighting output into account. Basically the index compares the area above the average light output to the area of the whole cycle.

Flicker index is therefore calculated: AREA 1/(AREA 1 + AREA 2)

The smaller the index is, the smaller the flicker is.

Devices

Luckily there are devices that can measure the flicker. For example UPRtek’s MF250N LED Meter is made for measuring all aspects of flicker. You can use it to  measure both of these metrics as well as the frequency of the flicker.

More information on this meter you can request here.

Why does LED Flicker?

The problem with LEDs is that they differ a lot from older lighting technologies. Tero wrote a post about LEDs and the basics behind this, so I won’t delve into that with much detail.

To be short, if LED is supplied with a constant current, it won’t flicker. But the current will have to be really constant.

The most common reason for LED flicker is a bad LED Driver. If the driver fails to provide constant current, the led that it powers will flicker.

As the driver converts the AC to DC, there will be some ripple, which will cause the frequency to jump typically to the double (as it was with fluorescent lamps). This means that the LEDs waveform will follow the driver’s waveform.

Flicker on drivers is called ripple. Basically it is a synonym for flicker.

Other reason for LED Flicker is dimming. If the dimmer controls the LED with lower frequency than 200Hz, it will cause significant flicker. This is due to the fact that some dimmers alternate the current that the LED is supplied with.

How to reduce flicker in LED applications

Well, I think that it’s kind of self-explanatory: get a driver with lower ripple. As I mentioned the driver is the key to the amount of flicker. You will need to think that whether the application can tolerate some flicker or not. Generally these low drivers cost more than the ones with high ripple. Its worth noticing that every driver has some kind of ripple.

If you have any comments, please feel free to leave your comment below. If you found this useful, please share this post.

How to select modules + driver package

In this blog post we concentrate on how to design a LED lighting package as a whole. And what different aspects you will have to take into account when selecting a light source and a driver.
I decided to write this as a case example so that the post is more concrete.

Most of the luminaire projects starts with the need for certain amount of lumen needed out from the luminaire. Then there can also be requirements for the shape and size for the light source. Color temperature, color rendering and lifetime expectancy might also be critical, but those are topics for a blog posts of their own.

LED Modules

LED Module

Case example

So in this case you have specified that the luminaire needs to achieve:

  • Lumen output 2000lm
  • Color Temperature 4000K
  • Ra(min)80
  • Lifetime 50 000 hours (LM70 for the whole luminaire)
  • Efficacy >120lm/W
  • Linear light source. Max length of 120cm

With these specifications, the finding of the suitable solution shouldn’t be a problem.
There are, however few things that have to be taken into account when looking at the data of LED modules:

  1. Lumen output: Some of the lumens from the light source will be lost due to the optics. The amount of lost lumens is around 10%. Therefore, you should look for light sources that can give you at least 10% more lumens than you need.
  2. The shape of the light source. Do you have a minimum size for the light emitting surface? The luminaire in this example can be built with modules around 30cm in length, but that would probably not be perfect fit your luminaire. It would leave a lot of empty space and the light distribution wouldn’t be even.

With those two in mind, you would need a light source that gives you roughly 2200lm and fills the whole 120cm evenly. That could be reached with for example 4 modules with lumen output of 550lm and length of 30cm or with two modules with 1000lm output and length of 60cm.

Selection of LED Drivers

Selection of LED Drivers

The Driver

For the case study presented above, you still have one more step to go: choosing a LED driver. Esko already wrote a good guide on this, so I’m going to be brief.

Before we can start, you have to specify one thing: How many LED modules do you want to drive with one LED driver? Only one module or several modules in series?

In this example you would probably want to drive all the modules with just one driver. This might be the case with all luminaires. In more complex lighting systems you might use several drivers. To find a suitable driver you will need to:

  1. Check the current that you want to drive your light source(or sources) with.
  2. Check the voltage of your light source (or sources) and check that it fits the driver’s voltage range.

You should always leave some room for the voltage as there might be some variations in the diodes. Check that the driver has around 10% lower minimum voltage and 10% higher maximum voltage than your light source.

So there you have it in brief. If you need more help or would like to leave a comment, please leave a comment or contact me!

You can also use our free tool to build your luminaire.

How to affect the lifetime of a LED module

How to affect the lifetime of a LED module

Lifetime of a LED module? What it means? Does it mean that LED module does not function anymore after the defined lifetime value? How to determine lifetime for the LED module? This post tries to explain what different lifetime estimation curves mean and how to interpret them.

Few terms have to be defined so that we can understand the lifetime for a LED module. First of all, the LED component itself, a tiny or a little bit bigger one, defines the lifetime of a LED module. Usually in normal conditions, all the other components last longer than the LED.

Some of the key parameters to evaluate LED module lifetime are listed below:

  • TC temperature = the temperature that can be measured from the LED module’s TC

This is usually placed so that it is as near to one of the diodes in the center part of the module as possible. This means as near LED component’s soldering pad on the PCB as possible.

LED Module, the point in the middle with the marking "TC" is the TC-point

LED Module, the point in the middle with the marking “TC” is the point where you measure the TC-temperature.

  • TJ temperature = the temperature of the PN-junction inside the LED diode.

This usually can’t be measured, but it can be calculated when the LED diode’s thermal resistance and the LED’s power consumption are known.

  • RTH = thermal resistance mentioned earlier. TJ = TC + RTH*PD, where PD is the power consumption of the LED diode.

Thermal resistance describes how well heat is transported out of the diode junction to soldering pad on the PCB. The smaller the thermal resistance value is, the better heat is transported away from the diode’s PN-junction.

  • LM or L = Lumen Maintenance.

LM value tells that how many percents of luminous output is still left from the original.

  • L80Bxx – the lumen maintenance lifetime

Bxx is a value at which xx% (e.g. 50%) of the products lumen output falls below 80% of the nominal initial value. If xx% is 50%, then it is expressed L80B50.

  • L80Fxx – the electrical failure time

Fxx is the value at which yy% (e.g. 10%) of the light source population has experienced conventional lights-out failure. If xx% is 10%, then 10% have experienced the catastrophic LED failure, other 90% of the LEDs continue lighting but at reduced lumen output level, was it then below or above 80% of the nominal initial value.

NB: It is very important to look at LED manufacturers’ lifetime estimates as some give the estimates as B values (for example B50) and some give the estimate as F values (for example F50).

Lifetime prediction for aLED Module at 700mA

Lifetime prediction for aLED Module at 700mA

How to design the LED module to have certain lumen output after certain operation time

There are few aspects that you should take into account when you want that your LED module operates more than expected operation time at the light output level that you, your customer or target application determines. If you for example require that after 50 000 operation hours of your LED module lumen output should be around 80% of the original lumen output value, you should consult your LED supplier. They will inform you the maximum TC temperature allowed for your LED component that this target will be reached. Or if your LED supplier gives lumen output curves versus operation time for certain TJ values, you should use the formula given earlier in the text to find out corresponding TC temperature.

When you find out the maximum TC temperature, there might still be some cases that you don’t reach the target lifetime. Then you should take some actions.

In the following there are some actions that you should think about if target hours are not reached:

  • Try using PCB with better heat conductivity.

Which PCB you have used? Is its thermal conductivity good enough to transport heat away from LED components that affect lifetime of the whole module? If you have used FR-4, why not to change it to Aluminum PCB.

  • Try adding larger heat sink or some other heat conducting elements.

Do you have effective heat sink under the PCB to conduct heat away from the PCB itself, not only from the LED components? Is there good thermal path from PCB to heat sink and have you used for example thermally conductive paste or tape?

  • Is there a way you could transfer the heat out from the inside of the luminaire?

Is your luminaire closed? Is there any way to transport heat away from the inner parts of the luminaire?

  • Think about separating light source and the power source.

The power supply also creates heat. Especially, if the luminaire is closed. Then it forms a closed system with two heat generating elements, the LED module and the LED driver. They both share the same heat load inside the luminaire, thus affecting each other.

Is there any means to divide the light source and the power supply, so that they are not in close contact with each other? Many times, if there is some kind of a metal profile into which the LED module is attached, the LED driver can be placed on the other side of the profile in order to avoid direct heat transfer between these two elements.

  • Can you leverage existing cooling solutions.

Ambient temperature(TA), affects the heat management of the luminaire.  Especially, if the luminaire is designed for application in some larger building, it can be possible to use for example building’s air conditioning system, to transfer heat away from the luminaire.

  • Can you change the driving current?

Of course, if you think the LED module itself as a single element and not as a part of a luminaire, also the driving current matters. Could you meet your lumen output requirements with smaller current during first years of operation? And when your light source’s lumen output starts to decrease in the course of years, is there a way to increase the driving current a little bit to reach the needed lumen output level after certain number of operating hours.

A table from aLED modules' datasheet. The typical current is 700mA, but you can drive it with as much as 1190mA. You can also drive it with much lower to save its lifetime.

A table from aLED modules’ datasheet. The typical current is 700mA, but you can drive it with as much as 1190mA. You can also drive it with much lower current (minimum in this case 70mA) to make its lifetime longer.

Those actions are some examples that you should consider to give your LED module required operation hours at certain lumen output level. Of course you should take the “big picture” into account: which kind of luminaire structure you have, which kind of driver you use and which kind of environment your luminaire is placed in.

Proper heat conduction and management are essential for long lifetime of your LED module! LED does not like heat.

If you have any comments or questions, you can post them in the comments.

What is COB LED

COB LEDs are very popular nowadays in LED lighting business. We talk and write about COBs, and our customers use COBs in their luminaires, but what exactly is COB? First of all, the abbreviation COB comes from words Chip-on-Board.

Citizen COB frontside, The yellow substance is phosphor, which turns the blue light of the chip white

Citizen Electronics’ COB frontside, The yellow substance is phosphor, which turns the blue light of the chip white

In COB packages many LED chips are usually attached to substrate with non-conductive adhesive. LED chips are wire bonded together to make different LED setups. The amount of single LED chips, inside a one COB LED package, can vary from few pieces up to several hundred pieces. Substrate is located on base material. Base material of COB LED is usually MCPCB or ceramic PCB. COBs often have blue diodes and use yellow phosphor layer to convert light to desired color temperature.

 

General drawing of a COB LED.

General drawing of a COB LED.

In early years of 21st century there were few SMD LED packages, which could be considered almost as COB packages due to their construction. Generally COB LEDs became available and popular in LED lighting market around year 2007. At first there were first quite a lot doubts towards COB LEDs in the market . Mainly because this package construction enabled LED manufacturers to put high powers in small package. Over then, this “high power” meant over 10W,

Also there was very little experience of COB LEDs, so these LEDs had a lot to prove.  Although now several lifetime tests have shown that COB packages are very reliable, if heat management is done properly.

When thinking about heat management, one important feature is thermal resistance. But it is worth noticing, that you can’t define which COB LED is better to conduct heat just from thermal resistance value. You should actually test LEDs in your own application.

Today COB LEDs are available from few hundred lumens up to 30,000 lumens. This means that

Citizen COB backside, aluminium PCB, which will conduct the heat to the heat sink effectivily. However it won't be enough to cool the LED

Citizen Electronics’ COB backside, aluminium PCB, which will conduct the heat to the heat sink effectively. However it won’t be enough to cool the LED

almost every light source can be replaced with COB LED. So available powers go from few watts up to almost 200 watts. The most powerful COBs require exessive heat sinks because they generate a lot of heat.

COBs offer great variety due to possibility to have many different LED setups even inside one COB package. Usually LED manufacturers have different lumens packages available in same size COB, so lighting manufacturers is able to use e.g. same connectors and optics in different solutions. Also it is good to remember that usually you can underdrive or overdrive COB LEDs and those might have quite wide driving range. This allows you to drive LEDs with very high efficacy, you can make balanced solution or you can make economical lumens.

COB LEDs are generally used in luminaires where lamp or single spot light sources have been used. So basically COB LEDs are used in almost every kind of luminaire. Although COB LEDs are used less often in linear lights or  panel lights, some solutions of that kind have been made with COBs. Luminaires which have really high luminous flux are usually made with more than one COB LED to distribute heat flux and to ease design of heat sink.

Sochi Olympic cauldron, Lights made using Citizen COB

Sochi Olympic cauldron, Lights made using Citizen Electronics’ COB (Copyright: Zers Pride LLC)

COBs offer very high luminous fluxes from small size packages and thus allow flexible design of luminaire. This gives you more freedom, when designing a luminaire. COB packages usually have excellent uniformity of light from light emitting surface, this is important e.g. if you want to avoid multiple shadow effect, which might occur with SMD based solution. It is also very easy to test COB LEDs. You only need COB LED, constant current driver and e.g. piece of aluminium, which can be used as heat sink.

LED Shadows: On the left, a shadow from a COB. On the right, a shadow from a LED with multiple light sources

LED Shadows: On the left, a shadow from a COB. On the right, a shadow from a LED with multiple light sources

We can see that COB LEDs have been very important development step in LED lighting business. This great package design has allowed to increase powers used inside one LED package tremendously. Also one good indicator of success of COBs is that today every major LED manufacturer and package maker has COB LEDs in their selection.

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