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How to Construct a LED Luminaire  

There are many aspects that have to be taken into account when constructing a LED luminaire. In this post I will give you some tips how to build a LED luminaire and which things have to be considered.

There are five steps for designing LED luminaires:

  1. The definition of lighting requirements; how much you need light in certain environment/space.
  2. Defining some design constraints and special requirements, for example related to optics or withstanding high temperatures.
  3. Optical, thermal or electrical design.
  4. The number of LED components is then calculated based on the lumen quantity defined in the specification.
  5. Finally, all components to construct the final luminaire, or prototype in the first stage, have to be defined and specified.

In this post, we concentrate on this last step, how to construct LED luminaires from lighting components rather than the step-by-step luminaire design process itself.

When you start the construction of a luminaire from lighting components, the first thing that you should decide is which kind of LED you use in your luminaire. Basically there are three different options:

  • High-power COB LEDs
  • Mid-power LEDs
  • Low-power SMD LED diodes.

In this post, I’ve divided the options to two different groups: high-power COB LEDs and mid- and low-power LEDs, which usually are SMD LED components.

High-power LEDs

COB Luminaire

Luminaire using Citizen COB LED

High-power LED option comes usually into question when there is a need for large luminous output. Citizen Electronics’ COBs are powered from 3W COB to 80W COB with typical power consumption values. The luminous flux ranges from about 100 lumens to 13 000 lumens with typical current and even to nearly 20 000 lumens with maximum operating conditions. When constructing a luminaire using COB LEDs there is a need for some kind of heat management because of large power density on small area that has to be conducted away from COB LED. The power density can be even 22 W/cm2 on light emitting area of about 8.5 cm2. Many times price target sets the limit for cooling, and active cooling methods can’t be used. This requires the use of passive heat management. In another words, you need some kind of heat sink. Typical material is some aluminum alloy with a fin-shaped structure in order to increase the overall surface area of the heat sink element. Additionally, some kind of thermal paste or other thermal interface material is inserted between the LED and heat sink in order to increase heat conduction from the LED to the heat sink and ultimately to the luminaire body.

Of course you need also LED driver to feed electric current to the COB. When talked about COB LEDs, many times you can drive only one or two LEDs with the same driver. Esko Väisänen explained the selection process of LED driver in his post: How to choose the right LED driver.

In addition to the COB LED and the LED driver, you may also need some optics, such as lens or reflector to increase light quality coming out of your luminaire. Current feeding to your COB LED can be realized either by soldering wires to the COB or using special sockets or connectors to supply power to the LED.

Mid-power and low-power LED

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

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

When constructing a luminaire using mid-power or small-power LEDs, heat management is not such a big problem as in the case of high-power LEDs. Normally the key target for luminaires using mid- or small-power LEDs is the light distribution or color consistency. Applications range from store lighting through emergency lights to decorative lighting, even to LED bulbs. Diffuser plates, for example opal diffuser or prismatic diffuser, can be used in these kinds of luminaires. The luminaire in which small- or mid-power LEDs are used include usually PCBs. The alternatives are usually FR-4 or aluminum metal-core PCB (MCPCB) on which SMD LED diodes are assembled. Usually, if the total power consumption of the LED module exceeds 10W, the aluminum MCPCB is used in order to better conduct heat away from the PCB. Depending on the case, some kind of extra aluminum profile can be used to conduct heat away. If the luminaire has a closed structure, you should also take care of the heat inside the closed luminaire. Heat should be distributed and conducted away from the LED so that the LED does not get too hot. FR-4 can be used for lower power modules by using enough copper pour to spread heat uniformly. FR-4 boards are also cheaper than aluminum PCBs and are used if price becomes the key issue and power consumption is not the problem. In addition to the PCB and the LED diodes some kind of connectors are necessary to connect the LEDs into the outer world electrically.

Also these luminaires need a LED driver to give current to LED components. In addition to heat formed inside the LED components themselves, heat forms also in the LED driver operation. This causes problems if the luminaire structure is closed as discussed earlier. If you use many modules within one luminaire, you will need some kind of cabling between the modules. When designing for example a linear luminaire, there may be a need for some cabling throughput. This will usually mean that cabling has to go on the other side through some plastic or metallic profile. Some additional screw holes may be possibly needed for attaching the metallic profile into the luminaire body.

If you have any questions or comments, please feel free to leave them on the comments field.

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.

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.