Author Archives: Taru Oksala

About Taru Oksala

Taru is responsible for marketing at Arrant-Light Oy.

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.

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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How to Choose a Suitable Constant Voltage LED Driver for Your Application

We discussed earlier about general characteristics of LED drivers and how to choose a suitable constant current LED driver for your application.  Now, I’m going to tell you how to choose a right LED driver for your constant voltage application.  As told in the previous posts, LED drivers are divided into two different categories: constant current and constant voltage drivers. But that is not the only thing you have to take into account when selecting the driver. In this post, we are focusing in constant voltage drivers.

Constant voltage drivers are generally used when you need a stabile voltage fed to your LED. You can check the datasheet of your light source whether it needs constant current or constant voltage. If it says for example 12V or 24 V, then it needs constant voltage. And for example 350 mA or 700mA means that you need a constant current driver. Constant voltage driver (power supply) keeps voltage constant (e.g. as 12 V DC), but feeding current varies according to the load (the higher the load the bigger the current)

Datasheet of Constant Current and Constant Voltage LED Module. The circled value tells you does the module need constant current or constant voltage.

Datasheet of Constant Current and Constant Voltage LED Module. The circled value tells you does the module need constant current or constant voltage.

With these easy step-by-step instructions, you will find a suitable driver for your luminaire or signage application.

Step one: What voltage does your LED application need?

As already mentioned, you should find the voltage that your LED needs, from the datasheet or from the product itself.  For example if your LED needs a voltage of 12 V, you should find a driver with 12 V DC output voltage. If LED demands 24V, you should find a driver with 24 V DC output voltage. So that is pretty straightforward.

Step two: How powerful driver do you need?

The power consumption of the LED application can also be found from the datasheet or from the value label in the product.

Remember that if using multiple LED components, you have to find a driver that can feed all the LED components in your luminaire (in parallel connection).

 

GE Lightech 12W, 12V LED driver

GE Lightech 12W, 12V LED driver

Step three: What current range you need from the driver?

Again take a look at the datasheet and check the current of the LED application. If you have multiple LEDs, you should add the current together. Then you should find a driver with a current range that your LEDs fit into.  On the other hand if you have checked well the power you need then your driver will give enough current to get your LED application burn on the right level.

And in some constant voltage LED applications the current is not mentioned at all, only the voltage and the power. Then you can skip this part.

Step four: Do you need dimming? And what type of dimming?

A need for dimming is mainly dependent of the specification of your LED application. If you don’t need dimming, a normal on/off driver is enough for you. If you need dimming, there are many different types of dimming, but that is a topic for another post.  But e.g. in signage applications dimming is not normally required.

Step five: What are the physical dimensions the driver has to fit into?

You should also consider if there are some limitations for the physical dimensions of the driver. These will obviously have an impact on your driver selection. You will generally find the physical dimensions of the driver from its datasheet.

Step six: is the driver placed inside the LED application or outside (built in or independent version)?

If the driver is placed outside the LED application without any fixing the driver should be classified as an independent version. This means that the input and output cables of LED driver have strain reliefs to secure safe cable connections in case of any pulling force.

Step seven: What kind of environment the LED application is used in?

Where is your LED application designed to be used in? If it is designed for indoor use, then you probably won’t need to think about IP-classification so much. Of course if the luminaire is used in a room with a lot of dust or moisture, this has to be taken into account.

And for outdoor use check that the product is approved for min IP67 area.

GE Lightech 200 W 12V, IP67 driver

GE Lightech 200 W 12V, IP67 driver

IP20 class drivers it means that this driver can be used in indoor lighting applications but hardly stands harsh conditions in outdoor lighting unless the luminaire itself is waterproof thus protecting the driver.

But when designing a luminaire to outdoor use, then you should check that that the driver has good enough IP-class.

Usually IP67 drivers are heavier in weight, driver electronics is molded in many cases with plastic (e.g. potted) and the electrical throughputs of the wires both on primary voltage and the secondary voltage side are sealed with required protection against moisture.

Step eight: Approvals, is the driver suited for European or American standards?

Does the driver have any approvals? And are the approvals for Europe (ENEC), America (UL) or for another area? This can generally be found from the datasheet of the driver. In most cases it is the benefit of both the customer and supplier that drivers are certified for that area where they are used.

ROAL Strato CV 24V with ENEC and UL approvals

ROAL Strato CV 24V with ENEC and UL approvals

So there you have it. With these steps you should be able to find a suitable LED driver for your application. If you don’t, please leave a comment or contact me directly.

What is aLED?

We released a new brand for our products; aLED. At first this brand is used along with our led modules, but later there will be more products to be labelled aLED.

There might be some people, possibly you, wondering what does aLED stand for? And why did we decide to create such a brand? Let me tell you.

aLED was formed during the spring and summer of 2014. There were many reasons behind the decision to create the brand and in this post I’m going open up those reasons.

Logo for the new aLED brand

Logo for the new aLED brand

  1. Warranty

We wanted to be able to give our customers a clear warranty. There can be many parties in the manufacturing process of a LED module. There is the PCB manufacturer, LED manufacturer, connector manufacturer etc. And all they give a different warranties and different conditions for those warranties. We wanted to give our customers a straightforward warranty:

aLED Module will last for at least 5 years. If it breaks while being used in a proper way before that, we will make it up to you.

  1. Delivery time

We got tired of the fact that the estimation of the delivery time for LED modules is guessing at best. PCBs are coming on one day, LEDs at another day and connectors on another. The company manufacturing the actual modules has time for production two months from now. We, and more importantly, our customers can never know when they get their products. We wanted to make this clear:

aLED Modules will be shipped in 48 hours after the purchase order.

aLED Module

aLED Module

  1. Variations in chromaticity

Our customers want to have guarantees that the module they order is actually near the right nominal color temperature. We have had these issues before and we know that everyone has had these issues. With the quality of the LEDs we use we can now guarantee the minimal variations in chromaticity.  So when you order your first module, all the following modules will have very little variation in chromaticity. To get an LED to exactly to a certain color temperature is near impossible, but we are working towards this.

  1. Right components

To be able to guarantee the quality of a LED module, all the components must be top quality. The modules are as good as the weakest link. We have taken a lot of time and effort to find the best possible components: the best PCBs, the best connectors, the best LED components and the best place to manufacture those modules.

  1. Customization possibilities

We know that our customers are different. For some the standard modules will be good enough and they can stand out with their luminaire design, price or some other factors. For some customers, the shape and type of the module is THE THING. That is the reason that we can offer customized modules to you. If you need soldered wires instead of connectors: you can have them. If you need customize shape with certain light distribution: you can have it. If you need anything else: you can have it. Delivery time might be a bit longer, but all the other guarantees still stand even for a customized module.

LED Module, which can be used in luminaire needing good light distribution.

Square shaped aLED Module.

  1. Best price

Everyone wants the perfect product for a perfect price. That’s what we have been aiming for. We have optimized the supply chain and negotiated good deals with component manufacturers. That is the reason we can offer you the best possible price.

These all might sound obvious, but they are not. We know that there has been problems and we have even had those problems ourselves. That is the main reason behind the aLED brand. We want to give you, our customers, a certain level of guarantee. We want to make the selection of LED module as safe and easy as possible.

Citizen COB LEDs generation 3 – What has changed from the last generation?

Citizen has released brand new generation 3 COB LEDs. Is this post I go through briefly what changes and advantages this update brings to Citizen LEDs.

First thing which is noticeable with new LEDs is that product code changes from e.g. CLL022 to CLU024. Third letter has been changed to ‘U’ to inform that generation 3 COBs are UL recognized components.

Most powerful of the generation 3: CLU054

Most powerful of the generation 3: CLU054

Citizen has managed to improve LED performance significantly in generation 3 products compared to the last generation. One of the main updates has been done to package performance, which has allowed better light extraction from generation 3 LED package. Other main update has been in LED die inside package. These new LED dies do not allow only better performance, but also give you the possibility to have even wider current range used with LED. In practice this means 50% wider overdriving range compared to generation 2 LEDs.

What is the best about these generation 3 packages besides great performance improvement is that outlines and mechanical dimensions remain the same. So you can easily update these new products to your existing luminaire designed for previous Citizen LEDs. This also means that all the accessories designed for previous versions still work with new LEDs.

When you are considering update from generation 2 to generation 3, please keep in mind that most probably you will find four suitable options from generation 3 LEDs to replace your existing LED. Generation 3 will give you much more freedom to choose from significant improvement in efficacy, getting balanced performance update or getting economical lumens with same efficacy. If you need help in the selection, I will be happy to help you.

Smallest of the new generation 3: CLU024

Smallest of the new generation 3: CLU024

Citizen has also increased minimum color rendering index for generation 3 from Ra65(min) to Ra70(min). These Ra70 products allow very high lumen output with excellent luminous efficacy. This also allows wider usage of high efficacy LEDs in places where Ra70 is minimum requirement.

If you have some questions or comments about Citizen LEDs, please contact me directly or comment below.

How to choose suitable Constant Current LED driver for your application

Selection of LED Drivers

Selection of LED Drivers

We discussed earlier about the general characteristics of LED drivers. In this post, I’m going to tell you how to choose a right LED driver for your application. LED drivers are divided into two different categories: constant current and constant voltage drivers. But that is not the only thing you have to take into account when selecting the driver. In this post, we are focusing only in constant current drivers.

Constant current drivers are generally used when you need stabile current fed to your LED. With constant current driver, it is easier to manage the right brightness. You can check the datasheet of your light source whether it needs constant current or constant voltage. If it says for example 350mA, then it needs constant current. 12V or 24V means that you need a constant voltage driver.

In this post, we’ll take a look at constant current drivers.

How to choose a constant current driver for your application?

With these step by step instructions, you will find a suitable driver for your luminaire.

Step one: What forward current does your LED need?

As already mentioned, you should find the forward current your LED needs, from the datasheet. For example if your LED needs a current of 350mA, you should try to find a driver with 350mA output current.

Step two: How powerful driver do you need

The power consumption of the LED can also be found from the datasheet or at least it can be calculated with the data in the datasheet. The power consumption can be calculated by multiplying typical driving current value by typical forward voltage value that both can be found in the LED data sheet. Sometimes you can even find the power consumption directly from the datasheet.

Remember that if using multiple LED components, you have to find a driver that can feed all the LED components in your luminaire.

ELT 10W, 500mA LED driver

ELT 10W, 500mA LED driver

Step three: What output voltage range you need from the driver
Again take a look at the datasheet and check the voltage of the LED. If you have multiple LEDs, you should add the voltages together. Then you should find a driver with a voltage range that your LEDs fit into.

Step four: Do you need dimming? And what type of dimming?

A need for dimming is mainly dependent of the specification of your luminaire. If you don’t need dimming, a normal on/off driver is enough for you. If you need dimming, there are many different types of dimming, but that is a topic for another post.

Step five: What are the physical dimensions the driver has to fit into?

You should also consider if there are some limitations for the physical dimensions of the driver. These will obviously have an impact on your driver selection. You will generally find the physical dimensions of the driver from its datasheet.

Step six: What kind of environment the luminaire is used in?

Where is your luminaire designed to be used in? If it is designed to indoor use, then you probably won’t need to think about IP-classification so much. Of course if the luminaire is used in a room with a lot of dust or moisture, this has to be taken into account.

ELT 60W, 700mA, IP20 driver

ELT 60W, 700mA, IP20 driver

IP20 class drivers it means that this driver can be used in indoor lighting applications but hardly stands harsh conditions in outdoor lighting unless the luminaire itself is waterproof thus protecting the driver.

But when designing a luminaire to outdoor use, then you should check that that the driver has good enough IP-class.

Usually IP67 drivers are heavier in weight, driver electronics is molded with plastic (e.g. potted) and the electrical throughputs of the wires both on primary voltage and the secondary voltage side are sealed with required protection against moisture.

ELT 10W, 350mA, IP67 driver

ELT 10W, 350mA, IP67 driver

Step seven: Approvals, is the driver suited for European or American standards?

Does the driver have any approvals? And are the approvals for Europe (ENEC) or America (UL). This can generally be found from the datasheet of the driver.

So there you have it. With these steps you should be able to find a suitable LED driver for your application. If you don’t, please leave a comment or contact me directly.

You can also use our Light Builder to select a driver.