Monthly Archives: February 2014

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.

SMD LEDs

SMD LED

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.

 

 

COB LEDs

COB LED

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

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.