Can I Use an LED Light Engine?

I like the long life and high energy efficiency of an LED. Can I buy one and install it in a light myself?

Yes, it is possible. However, first you will have to deal with choosing among hundreds of illumination LEDs to find the one that is right for your application. Once you do this, you will need to read and mostly understand a 15-page LED data sheet. Having mastered all that, you are ready to start the project!

So where do I start?

LED lights must be carefully designed into an application and the first place to start is with how you are going to get rid of the heat the LED generates. You'll need to add a heat sink.

Why do I need to do that? My incandescent doesn't need a heat sink.

Actually most of the energy heats up the bulb and all of its surroundings. It eventually gets carried away by natural convection because of the huge temperature differential between the bulb and the air around it. The main difference is that the light bulb is metal and glass, which can handle several hundred degrees, but the LED is a semiconductor that is fragile by comparison.

The LED heat is generated in the diode itself and if there is not a well-designed heat path, the heat generated will just increase the temperature of the LED chip. If the LED chip gets too hot, it will rapidly accelerate the degradation of the light over time. The result would be that your light output would degrade much sooner than the potential capability of the LED, which is generally 50-100,000 or more hours. Without proper heat sinking, the LED could lose half of its initial light output in less than 1,000 hours.

I surely don't want that. I notice the LED data sheet states that long life is directly related to keeping the case temperature of the LED under 50° C. How do I do that?

Well you should have studied thermodynamics in college. Just kidding. But, then again, you do need to know how thermal paths work and be able to calculate thermal resistance along those paths. We are getting to a point already where you may need an LED light engine.

Let's try something easier.

OK, let's discuss where you want to target the light output.

I don't ever have to think about that with my incandescent light.

True, the incandescent radiates in a 360° spherical pattern, so in many situations the light is mostly lost. That is, it does not land where you want it to land. However, with the LED light, the light pattern can be directed precisely where you want it to go. This increases the energy efficiency because most of the photons can be directed to the light target area and not wasted the way the incandescent does.

So what college degrees do I need to figure out how to direct the light to my target area?

You're catching on! You need a lens. Designing a lens to take an existing light pattern and change it to another light pattern takes us into the realm of non-imaging optics. It's a real specialty area requiring sophisticated light measurement tools to design a lens, and high-precision machine tools for fabricating the lens.

I think I am going to pass on the lens and just use an LED with more light output.

That's not very green, but I see your point. You may want an LED light engine.

I tremble at what's next.

Sorry, I don't mean to be scaring you. LEDs are a wonderful invention and the technology keeps getting better. They are our future lighting devices. However, we have not talked yet about how to power them up.

My gosh, you mean I can't just put a voltage across the darn thing?

Well, no. That's why we call it a light emitting diode. Here I am scaring you again, but applying a voltage across an LED will not only damage it but may blow it up! The LED is a diode and needs to be driven from a constant current source.

OK, let's stop right here. I've got to be a mechanical engineer, an optics expert and now an electrical engineer. Let's hear about this LED light engine!

Well, as you probably have guessed by now, an LED light engine solves everything. You define the application, how much light you need, the target area and the power source you want to use. For most common applications an LED light engine will be available to fill your needs. OptoElectronix has introduced a very useful LED light engine platform. It is called the ULE2000 series. A description of its capabilities, versatility and the many options that are possible can be viewed in our data sheet.

Not only can I use an LED Light engine, I will use an LED Light engine!

Yes, and it comes with the mechanical engineer, the optics expert and the electrical engineer built in.