Tag Archives: COB

Environmentally Friendly LED Lighting Components

Generally, we can say that LEDs are environmentally friendly and recyclable. They have a long lifetime and low power consumption. They don’t contain hazardous substances, for example, mercury as compact fluorescent lamps do. In this blog post, I will present to you four environmentally friendly luminaire component choices.

LED That Don’t Need a Driver

Have you ever looked inside the driver? In the picture above, you can see the inside of the small-sized one. Drivers are made of many different materials and components. That’s why they are hard to recycle. The fewer components product has, the easier it is to recycle. For example, an aluminium heatsink is easy to recycle, because it contains mainly aluminium.

Drivers are the most fragile parts of the luminaire. In general, they can be the first component that breaks from the luminaire.

All traditional LEDs needs a driver to work. Except for AC COB that can be connected straight to the mains power. Because AC COB doesn’t need a driver, luminaire can be a lot smaller than before. This gives more flexibility for the design. At the same time, you can save in logistics and packing. You can read more about AC COB from our blog post.

Same Lumen Output with a Smaller Luminaire

Size is an important feature when designing environmentally friendly luminaires. When you use less material the luminaire gets smaller. And by downsizing the luminaire you can save in logistics and packing.

One great way to make the luminaire smaller is Citizen’s HC COB. It has higher efficacy and lower terminal resistance. This means that you can use a smaller heatsink. Therefor luminaire gets smaller the and you can still get the same lumen output. As a result, it makes HC COB more environmental choice. Read more about HC COB from here.

The Right Amount of Light and Less Light Pollution with Right Optics

When we talk about LEDs, often we come up with light pollution. We can say that almost all outdoor light that doesn’t have a purpose is light pollution. This means that light always needs a target.

When you replace the old light sources (for example HPS-lamps) with same powered LED, you get a lot more light. This is not environmentally friendly. You get a lot of unnecessary light and same time create light pollution.

When we design luminaires with the same lumen output than before, LED saves energy. This is because LED has less than 10% of the incandescent lamp’s power consumption. That’s why it is important to think about lumens, not power when replacing lamps with LEDs.

LEDs light comes from a very small area and from a flat surface, so it is easier to control than a light bulb. In street lights, most of the light pollution comes from light that goes up and away from the road. It is important to choose optics for the luminaire which are designed to minimize the light pollution.

Control the Luminaires with Sensors

There’s a lot of different sensors for different applications. The most familiar ones are the on/off-sensors. They automatically switch the light >on and off  by movement. They save energy, as the light can never be accidentally left on. This type of sensors is already generally used in public spaces.

Another great way to save energy is to use daylight sensors. They react to the light that comes from the outside. This way you can maximize the benefits of the sunlight. For example, during the day, you don’t need as much artificial light as in the evening. Read more about sensors from this blog post.

We have already made big steps in ecology, but still, we have a lot to do. We need to think about the packing of the luminaire and logistics. It’s important to minimize the amount of plastic used in packing. Also, we need to think alternatives for air freight. Small choices really matter.

Below you can download a presentation about Citizen’s AC COB. If you have anything to ask, you can always email to me: taru.matikainen@light.fi

Download Here

Million shades of white LED

Nowadays LEDs have great efficacy and lifetime. They produce more and more light with less power. I think that it’s less important to increase efficacy because we have already reached what the market demands. What else we need from the light than a lot of lumens? In this blog post, I’ll compare the differences between white LEDs.

We all know that LEDs are available in different color temperatures. For example, Citizen 6 generation’s LEDs are available from 2700K to 6500K. They are also available in different color rendering indexes. Color rendering index simply means how well a white light source can show, or render, colors compared to sunlight. We know that the color rendering index does not always tell the whole truth (You can read more from this blog post).

Nowadays we need a light source that has good efficacy and color rendering, and it doesn’t hurt if the light source can be customized to use in many different luminaires. We want light source that brings colors vivid and alive. Also, design interiors with relaxing atmosphere.

Let’s look into what else affects the quality of light than the color rendering index and color temperature.

White without greenish tone

IMAGE: Black line in the picture is B.B.L. Red circles indicate below B.B.L. LEDs.

In some projects, we want a light source that makes white look whiter. Some LEDs may turn white into light green. Traditional white LEDs’ color temperature chromaticity is on or very near B.B.L. (Black Body Locus). Citizen also produces below B.B.L. LEDs. Their color temperature is below the B.B.L. line. As you can see in the picture, above the line is greenish colors and below the line is reddish colors. Below B.B.L. LEDs make white look pure white and it also renders red colors better. This way we can create light that doesn’t have a greenish tint.

Below B.B.L. LEDs are very popular in shop lighting and everywhere where brisk atmosphere is needed.

Read more about the color temperature from this blog post.

More attractive display with high color contrast

The general color rendering index (CRI) is defined as an average of the sum of first eight R-values. However, these first eight indexes are rather less saturated colors, while indexes R9-R12 represent highly saturated colors. This means that the same CRI doesn’t mean same color rendering.

The Citizen’s Vivid LEDs make colors seem brighter with better color contrast. The spectrum of light has been designed to have as good as possible saturation. This way Vivid LEDs can render bold colors vividly. With better saturation, you can read easier for example newspaper under the Vivid LEDs.

Below you can see a picture where Vivid LEDs are compared. The higher the bar is, the better the color renders. The comparison is done to halogen bulb (0= halogen bulb performance).

Great use for Vivid LEDs are places where good color rendering and concentration is needed, for example, clothing and cosmetic stores, art galleries, schools, hospitals, and offices.

There are two different Vivid LEDs:

  • Brilliant Vivid – Very high color contrast.
  • Natural Vivid – High color contrast.

Vivid LEDs are meant to be combined. Use Brilliant Vivid as spotlights to bring color and textures up, and Natural Vivid as base light because it has better efficacy but has still very good color rendering and contrast.

Change the color temperature of light

Everyone is now talking about “human-centric” -lighting in the lighting industry. It means that by changing the color temperature you can maximize productivity and improve concentration or create comfortable atmospheric feeling. Citizen’s Tunable White is a great solution for “human-centric” -lighting. Its color temperature can be changed freely from 2700K to 6500K. This means that you can achieve warm light like incandescent lamp and daylight with only one module. In addition to changing the color temperature, you can also dim the brightness.

Early Tunable White products have been big sized modules. Citizen’s Tunable white is as small as the COB. This means that you can make a lot of smaller Tunable White luminaires than before. The small size also gives more even light. The spots between cool and warm dies are practically invisible, which guarantee more smoothly light.

By connecting Tunable White into the right control unit, you can change the color temperature and brightness according to the time of day.

Light that gets warmer by dimming

One of the features of the halogen lamp is that when dimmed its color temperature changes warm-toned. Citizen’s Dim-to-Warm COB-LED does the same thing.

Dim-to-Warm is a COB-LED, so you don’t need any complicated special features from the driver, like two-channeling or programming features. Ordinary triac dimmable driver is enough. Dim-to-Warm COB has preset dimming curve, so when you dim it, its color temperature changes automatically just like halogen.

I hope that this blog post gives you some new thoughts for designing the luminaires. When you use any of the LEDs that I just presented to you above, you’ll get a luminaire that has more to provide than just ordinary light source. This way you can have competitive advantage.

You can download presentation about Citizen LEDs below. If you have anything to ask, please do not hesitate to contact me. My email address is taru.matikainen@light.fi and I’m always happy to help you.

Download Here

Why Heat Pipe is Better than Traditional Heat Sink?

You will need a heat sink when you use a COB led for your luminaire. The traditional way of transferring the heat away from the light source is to use passive aluminum heat sink. In this post, I introduce another solution for cooling the led: Heat pipe.

Traditional heat sinks are based on the fact that aluminum transfers heat away from the light source. The higher the power of the led is, the more you need aluminum.

This grows the luminaire’s size and makes it more expensive. The bigger size of the luminaire makes logistics costs go up and increases the price for end user even more.

There is another solution for the high power leds without the need for noisy fans etc: Heat pipe.

Heat pipe technology is traditionally being used in computers and for example in satellites. But now it is available in lighting.

Furukawa Heat Pipes (HYC Series)

Furukawa HYC Series uses heat pipe technology to transfer the heat and makes heat sinks more efficient in cooling the LED.

how heat pipe works

How Heat Pipe Works

Heat Pipe’s thermal conductivity is almost 200 times better compared to copper. This allows the heat sink to be a lot smaller than we are used to.

Smaller heat sink reduces the weight of the luminaire dramatically. This reduces the transportation costs as well as the amount of other materials needed.

The heat pipes effectively transfer heat from the heat source throughout the whole heat sink cooling the heat source faster than ever.

Unlike many Chinese manufacturers, Furukawa uses oxyzen-free copper in its heat pipes, which means that their lifetime is over 20 years.

Heat Pipe vs. No Heat Pipe

Heat Pipe vs. No Heat Pipe

Save money and environment with our product

aLED Engine

aLED Light Engine (Furukawa heat pipe + Citizen COB + optics + aLED Driver)

Now I want to introduce you our own aLED Light engine that uses Furukawa heat pipe with Citizen COB. aLED Light Engine produces over 40.000 lm and weights only 1 kg (without driver and optics). And only 3.6kg with optics and driver.

By combining Citizen COB and heat pipe technology, you can build luminaires that:

  • Produce a lot of light
  • Are light in weight and small in size
  • Save environment
  • Are completely recyclable

Heat pipe is very lightweight. You can get a lot of light with a smaller luminaire.

Furukawa heat pipes are compatible with Citizen CLU04x and CLU05x COB leds.

Download an example of different led + heat pipe combinations and datasheets for custom models with screwholes for Citizen COBs.

Download Here

How to Connect a Single LED Component into AC Network

I have two blog posts for you focused on how you connect COB LED components into the electrical network. I mean, when you have either a single COB LED or an LED module based on SMD LED components assembled on a PCB board.

Compared to traditional lighting, connecting LEDs to the electrical network is a whole new world. LEDs need direct current (DC) to light them, alternating current (AC) will not work. There are also AC modules available but those are not covered here.

In this post I will concentrate on connecting single COB LEDs. In case you are interested in connecting LED modules, I will write about that in my next post.

LED driver

You will need an LED driver, which is actually an AC/DC converter. It converts the AC voltage/current of the electrical network into the suitable DC voltage/current needed by the LED component. You will find the requirements of the LED from a datasheet provided by the manufacturer. If you need help in choosing a driver, you can read our guide.

Figure 1. Example of an AC/DC converter, LED driver. This one is from ELT with dipswitches, which means that you can choose the driving current.

Connecting COB LED into the AC network

In case of COB, you will have to create a closed electrical circuit so that the electrical current can flow through the LED component. A COB LED is basically a diode in its electrical nature: the current can flow only in a forward mode. This means that you must connect the positive (+) solder pad of the COB LED into the positive terminal of the LED driver. In the same way, you connect the negative (-) solder pad of the COB LED into the negative terminal of the LED driver. See the Figure 2 below.


This way, you create the closed electrical circuit that is needed to feed current through the LED so that it gives light. This closed electrical circuit formed by the LED driver and the COB LED is called the secondary side of the LED driver. LED driver feeds the power and current into the closed electrical circuit, and thus through COB LED, on the secondary side.


Figure 2. COB-AC Network


On the primary side, the LED driver gets electrical power from electrical network, AC network. The terminals of the LED driver on the primary side are called line and neutral. They are connected into the line and neutral connections of the AC network. If you have an LED driver with cables, they are usually blue (neutral) and brown (line). Some drivers also have a ground terminal, which is usually connected to the luminaire body with grounding wire. However, the closed electrical circuit is needed also on the primary side; between the network and the driver.

Usually, you will need to use some kind of terminal block to connect the driver into the electrical network on the primary side.

Picture of a terminal block

Figure 3. The example of terminal block to connect the LED driver into the electrical network.

Two options

Finally, as for physically connecting a COB LED into the LED driver, you have two ways to do it:

  1. solder the wires on the solder pads of the COB
  2. use solderless connectors.

In the first method, you manually solder the wire by using soldering iron with high temperature that melts the soldering material such as tin. After cooling, there is a joint between the wire and the COB solder pad. You need two wires, one for plus and one for minus solder pad.

In the second method, you use a solderless connector.

Figure 4. The solderless connector.

The solderless connector does the same effect as the soldered wire. You need the electrical connection also in this method, but you won’t need to solder the wire by melting tin. You just push the wire into the push-in terminals of the connector. Again, positive to positive and negative to negative terminal. They are marked on the connector. Basically these push-in terminals work with a combination of metal plates and springs that then make the connection to the solder pad of the COB LED.

The difference between these methods is, that unlike with soldered joints, in the solderless connector method the springs may loosen a bit over time and loss of contact may occur. Solderless connectors are generally thought to be more expensive than manual soldering.  

In my next post I will go through the steps for connecting LED modules.

Thank You for Everyone at Elfack 2017

I would like to thank everyone who we met at the Elfack Exhibition in Gothenburg, Sweden.

We had some good conversations with our existing customers as well as new people. This year we tested the color quality of Citizen’s LEDs at our stand. We got many answers through our questionnaire and found out that many visitors were excited about this new way of lighting.

If you took part in the test, you will receive the test results soon. We will also share these results with the public a little later.

We had a chance to show you our new products and the feedback we got from you was very encouraging.  I went through all the products in my last blog post, and if you wish to download more information about them, you are most welcome to do so here.

The products displayed at Elfack include:

  • aLED Engine
  • Citizen Gen 6
  • AC COB
  • Citizen Vivid Series
  • Furukawa Heatpipe
  • Merrytek sensors
  • Letaron & aLED Drivers

Our personnel will contact you as agreed, if they haven’t already. In case you have anything to ask, you can contact us directly.


What We Are Presenting in Elfack?

Elfack exhibition will be held in Gothenburg, Sweden from 9th to 12th of May. As it has been with previous exhibitions, we will be releasing new products and presenting the latest technology at our stand.

This year we will introduce and present the following products at our stand F04:70.

aLED Engine

aLED Engine

aLED Light Engine

We designed aLED Engine for applications that require a lot of light. aLED Engine consists of Furukawa heat pipe and Citizen COB LED.

In addition you can also choose a suitable optics and LED driver for the light engine from our selection. Suitable drivers are available as on/off, 1-10V dimming and DALI dimming.

aLED Engine is also compatible with Merrytek sensors, which allow you to control the lighting as you wish.

The 300W engine produces 36.000 lm at 4.000K and weighs only 3,6 kg with a driver installed.

aLED Engine will be at our stand in Elfack. There you can see the engine in action and try it with a daylight sensor.

Download More Information

Furukawa HYC Series

Furukawa HYC Series uses heat pipe technology to transfer the heat and makes heat sinks more efficient in cooling the LED.

how heat pipe works

How Heat Pipe Works

Heat Pipe’s thermal conductivity is almost 200 times better compared to copper. This allows the heat sink to be a lot smaller than we are used to.

Smaller heat sink reduces the weight of the luminaire dramatically.

The heat pipes effectively transfer heat from the heat source throughout the whole heat sink cooling the heat source faster than ever.

Heat Pipe vs. No Heat Pipe

Heat Pipe vs. No Heat Pipe

Furukawa heat pipes are compatible with Citizen COBs.

Furukawa heat pipes will be at our stand so you can see and try how light they are.

Read more about Furukawa heatpipe from here.

aLED & Letaron Drivers

aLED Driver

aLED Driver

aLED and Letaron offer a versatile range of both constant current and constant voltage drivers from low to high power (from 1 W up to 600 W).

Ouw own aLED drivers are best suited for high power applications. They are all available in IP68 and can be ordered as on/off, 1-10V dimming or DALI dimming.

Letaron drivers are best suited for low power applications, although they are available up to 52W.

Letaron offers a variety of designs to suit your needs including round, rectangular and slim models.

The Letaron low power drivers are also compatible with OLED light sources.

aLED and Letaron drivers will be on at our stand so you can see and try them yourself.


Merrytek sensors

Merrytek offers a wide range of different sensors. Some sensors come with LED driver and some are independent and can be connected to LED driver.

Merreytek has products particularly designed for eg. homes, schools, stairways, warehouses, offices, parking garages and outdoor use.

Merrytek’s intelligent lighting control products include:

  • Microwave motion and daylight sensors
  • Dimmable LED drivers
  • LED drivers with intergrated sensors

There will be Merrytek products on display at our stand. We will have an aLED engine wiht Merrytek’s daylight sensor on our stand, so you can see how it functions.

Citizen Gen 6, AC COB &Vivid Series

Citizen released Gen 6 COB and AC COB earlier this year with improvements compared to the previous versions.

Thermal Resistance

Thanks to better heat resistance, you can use much smaller heat sink. Gen 4 on the left, Gen 5 on the middle and Gen 6 on the right.

For the new Vivid series we’ve prepared a demo wall at Elfack for you to examine the possibilities of color quality control in LED lighting.

Seminar about color quality

We will organize a seminar about color quality on the first day of the exhibition.

Color comparison Vivid COBColor Comparison Regular COB 3000K Ra80 vs. Vivid Brilliant

The seminar will take place on Tuesday 9th of May.
Time: 16:00-19:00
Place: Hotel Gothia Towers, Tower 1, meeting room R22-23

The program:

  • Doors open at 16:00
  • Coffee
  • Welcome / Arrant Light Oy by Janne Mäkinen, Managing Director / Arrant-Light Oy
  • Color Quality with CITIZEN by Kosuke Tsuchiya, Field Application Engineer / Citizen Electronics Co.
  • Demonstration and open discussion
  • Refreshments and snacks
  • Close at 19:00

Please sign up for the seminar as soon as possible or latest by April 30th. We have limited seats and there is room for the first 20 persons only.

Sign Up for Our Seminar

Welcome to visit our stand F04.70 at Elfack.

All datasheets and other material will be available from our website soon. If you wish to download material about these new products before the exhibition. You can do that here.

AC COB – Easier way to make a luminaire

What is AC COB?

AC COB is brand new AC LED solution from Citizen Electronics. It is available with holder which contains necessary components to connect package directly to mains voltage. So basically it is designed to make life of luminaire manufacturer easier.

AC COB With Connector

AC COB With Connector

What advantages?

AC COB has integrated circuit which allows you to control luminous flux more accurately. For all CCT and CRI versions you are able to have exactly same luminous flux from the package e.g. 750, 1000, 1500 and 2000 lumens.

5 volt output enables you to use e.g. motion sensor, so you can easily adapt external sensors to easily add features to your luminaire.

There is no additional losses from driver and so there is no problem to have good efficacy even with low powers. AC COB with new integrated circuit has good compatibility with dimmers, you are able to dim this solution with Triac (leading-edge) and Transistor (trailing-edge) dimmers.

Small form factor and no need for external driver allow even more creativity to luminaire design. There is no need to worry where to place the driver.

What you need to take to consideration?

AC COB has of course similar characteristics than normal COB meaning warmer CCTs have lower efficacy than cooler CCTs. With fixed luminous flux, that means you have difference in power. So 2700K Ra90 AC COB consumes more power than 5000K Ra80.

And of course AC is still AC. If you don’t use more complex circuitry to modify AC to DC, you will still have AC characteristics affecting luminous flux. Mainly with AC LEDs this means that you have flicker present in light source. To reduce that effect, it is good to consider e.g. secondary optics which lower this phenomenon.

AC COB In Connector

AC COB In Connector


Even though AC LED might have it’s limitations it has certainly some advantages which make it viable solution as light source. It has ENEC certified components which are easy to use to design new luminaires and you can make testing with this solution in different luminaires. Now it is time to consider where you could use AC COB to realize its advantages.

You can download datasheets and brochure from the button below.

Download Here

Vivid LEDs: Special Color Rendering With Spectrum Tuning

When we talk about color rendering, traditionally that conversation has been filled with CRIs and Ra-indexes. These traditional ways of telling how well certain light source represents sunlight have been criticised because they may not tell the whole truth.

In recent years, LED manufacturers have been trying to answer this criticism by creating different products. Terms like “premium white”, “crispy white”, “pearl white” and “vivid white” have come to LED markets.

Despite the different terms, they are all meant for the same purpose: To represent certain colors and make the lighting look better. I will be using term “Vivid” as it is the term Citizen Electronics uses. And to be honest, it describes the purpose of these LEDs quite well.

Color rendering

Color rendering means simply how well a white light source can show, or render, the true colors of different physical objects compared to sunlight. You know the effect when you buy a jacket in the clothes shop and it looks completely different in sunlight.

Colors are divided into 15 indexes (R1-R15). A general color rendering index (CRI or Ra-index) is defined as an average of the sum of first eight indexes (R1..R8). However, these first 8 indexes are rather less saturated colors, while indexes R9-R12 represent highly saturated colors (red, yellow, green, blue).

CRI 100 = Sunlight

For example, in grocery stores, a shopkeeper may want to highlight red color of meat or colors of vegetables. This means that the general color rendering index doesn’t really tell anything about the rendering capabilites of the light. In this case, high rendering index of some of R9-R12 indexes is necessary. It doesn’t matter how high the CRI is, R9-R12 can be anything.

CRI 83 (look at R9)

CRI 83 (look at R9)

The above image shows the index values of R1-R15. The CRI is 83, but look at the R9 value. Not very good.

So basically, the LED itself can have the CRI of 97 and you still have no idea how does it render red or green for example.

Vivid via Spectrum tuning

Vivid LEDs are made using spectrum tuning. In short, this means that the phosphorus of the LED has been modified. How it is modified, depends on the LED and the intended application. Note that spectrum tuning can be made also by using RGB-LEDs.

For example, Vivid White LED’s spectrum has been tuned so that it represents white and bright colors as well as possible. The colors are more saturated than under typical normal LED light.

Test report on Vivid White aLED Module

Test report on Vivid White aLED Module. Click the image to open it in new tab for better view.

These LEDs work very well for example, in clothing stores, where you have a lot of different colors that need to look good.

Here are two good principals when choosing LED:

  1. Think about your application, what colors do you want to highlight?
  2. Don’t stare at the CRI (unless you get a full report), it might not tell everything


Traditional way of thinking color rendering solely through the CRI should be updated. More importantly, you should know what you want to highlight and ask for a LED suited for your application.

Download More Information About Vivid


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 the right LED?


There are tons of different LEDs even in one manufacturer’s selection so how on earth can you find the right LED for your solution?

In my previous post I discussed about the basic characteristics and operation principles of LEDs. In this post I will discuss about different packages and about the facts that will probably have an impact on your selection.

I will divide LED light sources into three categories:

  • SMD LEDs
  • COB LEDs
  • LED Modules

I will now look more closely on these three categories before we jump into the actual selection.



Citizen CLL600 – Example of SMD LED

SMD LEDs are small diodes used in LED modules. They have to be assembled on printed circuit board (PCB). Generally they allow you to design any kind of luminaire and allow you to make uniform light source. On the downside, SMD LEDs always require them to be assembled on a PCB.





Citizen CLL052 – Example of COB LED

COB = chip-on-board. COB is a small package that combines many diodes as a one light source.  COBs have generally small dimensions and produce a lot of lumens. You can attach COB directly to the heat sink, which allows excellent heat management.  COBs don’t need a lot room in the luminaire fittings and are therefore well suited for luminaires with small room for light source.

LED Modules


Example of LED modules – Linear and rounded

LED Modules are made of SMD LEDs and PCB. LED distributors offer standard modules which in general are made for the common need. For example we have different sizes of linear modules as well as rounded modules. These modules have a certain lumen package which remains the same from LED generation to another. This enables lighting manufacturer to update their luminaires with more efficient LEDs. If you can’t find a suitable LED module for your application, you can always contact a manufacturer and ask them to design a custom module for you.


How to know where to start

The main thing that has an impact on your LED selection is, obviously, the type of luminaire you are manufacturing.  If you are transforming an old luminaire into an LED luminaire, then you will probably have some demands on the physical dimensions of LED.

For example, if you have a T5 or T8 fluorescent lamp, you will need a light source that

a) gives you linear light
b) gives you uniform light
c) fits in to the old luminaire’s body

If you are not restricted by physical dimensions, then you have a lot more options.  For example if you are building a whole new luminaire, the physical dimensions are not so critical. Or at least you get to decide what are the physical dimensions the LED needs to fit into.

COB Luminaire

Luminaire using Citizen COB LED

The other important criteria for LEDs is the amount of lumens you need. You might have an older luminaire that you need to replace, so ideally you would want as much light as the old one produces. So for example, if you have a 120cm fluorescent lamp and it produces 2700 lumen you will want a light source that:

a) fits into the 120 cm long body
b) gives you uniform and linear light
c) gives you  enough light (you won’t necessarily need 2000lm if you have better optical efficiency)

So in this example, you could use for example two modules that are less than 600mm in length and produce 1000lm each. Or you could use smaller modules, for example four modules that are less than 300mm in length and produce 500lm each.  As you may have noticed this selection does not give you the same amount of lumens from light source, but you will still get the same amount of lumens out of the luminaire.

Then there are obviously the color rendering index (CRI) and color temperature (CCT), both of which are mainly depending on the application of your luminaire. For example if you are building a luminaire for a clothing store or an art gallery, you will probably want as high color rendering as possible. On the other hand if you are manufacturing a street light, you probably won’t care about CRI so much.

If you need any help with selecting the LED, or if you disagree with any of my views, you can share your thoughts on the comments below.