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LED System Design: You Get What You Pay For

LED lighting can clearly have advantages over traditional lighting technologies. LEDs can have a long lifespan (>50k hours), use less energy, and provide more flexibility in a lighting design. However, a poorly designed system, or making too many compromises on cost, can cause LEDs to underperform relative to expectations.

When designing, the process all starts with the LED selection. While there is a wide selection of manufacturers and LED types to choose from, most LEDs are designed for specific applications. These applications include, but are not limited to:

  • Portable (flashlights, medical headlamps, etc.)
  • Signage (full video, variable message, traffic lights, etc.)
  • Backlighting (TVs, handhelds, etc.)
  • Transportation (planes, trains, automobiles, etc.)
  • General lighting (luminaries and LED bulbs)

Furthermore, there are LEDs specifically designed for sub-segments of these applications. When selecting the LED for an application design, it is important to choose one that can perform within the appropriate lifespan, efficacy, color shift, uniformity, thermal, electrical, and optics expectations. The manufacturer should be able to support the customer’s expectations by providing the necessary data to prove an application's quality. While it can be tempting to select the most cost-effective LED, designers need to be careful of the potential compromises that choice may entail.

Thermal design is an important next step in the process. Designers should be sure they have the necessary space within the envelope to design a heat sink to effectively keep the LEDs in the system cool. For example, a 100W-equivalent A-19 replacement LED bulb does not exist — yet. Designing a system without adequate thermal management will also cause the LEDs to potentially underperform customer expectations.

Optical design is an important consideration as well. Directing the light effectively onto the required target will minimize the number of LEDs and power required to drive the system. This could, in fact, lower the overall cost of the system.

Designers also need to consider electrical design. LEDs are current-driven devices. There are several ways to design a constant current driver. Drivers that are simpler and more cost effective tend to be less efficient as well. Depending on the application, it is important to select the appropriate driver to meet the desired results.

Solid-state lighting solutions are only as strong as their weakest component. Depending on the application, designers should be aware of the allowable compromises they can make in order for LEDs to become the leading technology light source.

13 comments on “LED System Design: You Get What You Pay For

  1. Himanshugupta
    April 25, 2011

    Thanks Werner for this summary. How much cost difference is there between the intentionally poorly designed LED and the proper one? Also can a poorly designed LED still outperform the conventional light bulb?

  2. SunitaT
    April 25, 2011

    “Optical design is an important consideration as well. Directing the light effectively onto the required target will minimize the number of LEDs and power required to drive the system”

    Werner, I agree with you that  this is very important point in design because we usually need mutliple LED's to realise properly lit ambience. Are there any softwares available to perfrom optical design ?

  3. Jay_Bond
    April 26, 2011

    Excellent article explaining some of the thought processes for LED systems. One question I have is on the general lighting set up. As more companies are trying to market LED bulbs to businesses and homeowners as a more cost efficient route, is there information out there to help design a system? As people change to CFL's from incandescent, the lighting is slightly different. As the change goes from CFL's to LED's, even more thought needs to go into place. At the current price of these lights and bulbs, some purchasers will be disappointed without proper guidance. 

  4. elctrnx_lyf
    April 26, 2011

    It is not true that poorly designed LED light can still out perform the CFL light. Poor design might cause many problems which will initially rresult in reduce in performance and finally may actually completely broke. I accept with the statement the solid state lighting is only as strong as a weakest component in the design. This is true because solid state lighting involves more components like PCB, LED's, driver chips and also few passive components. But a CFL are manufactured with stable manufacturing process which is in existence for quite a long years already.

  5. Ms. Daisy
    April 26, 2011

    Thanks for the information on LED lighting designs. My questions are, how do I know that a designer is not intentionally using less “wattage”? Is there any form of consumer protection mechanism to identify such bad designers other than references from people the designer has worked with in the past?

  6. LifeLongLights
    April 26, 2011

    As a LED consultant these are my quick keys to analysing any LED bulb.

    1. Where is it made. Chinese bulbs use old technology and often times try to replicate a product made elsewhere with an abandon for solid design. This leads to:

    Faster bulb dimming: LED's don't just burn out they get dimmer and dimmer, this is most often caused by the overheating of the led and chipset. A chinese LED works much better if it is blinking or only used for short periods as it won't heat. Just recently the department of Justice in Washington bought 150 Chinese PAR-38's for a new courthouse. These bulbs melted from their alluminum housing and fell to the floor, just the led's the rest was still screwed in. We also conducted a test for a Fortune 100 company with troffers and the Chinese T8/T12 replacement lights had dimmed by 30% in 7 months while ours was still at original brightness.

    2. Look at a bulbs lumens and divide this by the wattage. This will get you its efficiency and allow you to compare bulbs with different wattages.For example the MR-16 bulb I sell works at 4.5 watts and puts out 420lm. This is an efficiency of 93.333 lumens per watt, the average incandecent is 10lm/watt so a 100watt bulb has 1000 lumens. Here is a comparison I have of lumen efficiency of some LED companies http://bit.ly/dZzmJw please let me know if you find any more that I should add.

    And a simple rule of thumb is if you can find a LED with a lower wattage and comparable brightness, choose that one because the light will depreciate at a slower rate due to reduced heat load.

  7. Werner Mashig
    April 26, 2011

    The cost difference between a poorly designed LED system and the proper design can be small to significant depending on the compromises one would make. 60 Watt equivalent LED light bulbs are just starting to hit big box stores now. Until recently, it was impossible to meet this requirement, mostly because of the amount of thermal mass needed in the design. Lifetime, efficacy, color consistency and color uniformity are key metrics to consider when designing this type of application. If all these metrics are important in ones design, then a poorly designed led system can never outperform any conventional lightbulb.

  8. Werner Mashig
    April 28, 2011

    There are many different softwares available on the market. One type of software, typically used by lighting designers and architects, is light rendering software. This type of software allows a user to build an environment similiar to what they would have in a real life setting. Files readily available from fixture manufacturers can be imported to render the effect the light will have on the environment. The second kind of software used is more for optical lens and reflector design. This type of software allows a user to customize an optic to shape the light exactly on their target area.

  9. Werner Mashig
    April 28, 2011

    There is no doubt that one of the critical things to progress the adoption of LED lighting is education. LED system design does not need to be a bulb. The easy way to retrofit an existing fixture, that was designed with traditional technology, is by using an LED bulb. However, as the adoption progresses, you will see lighting fixtures designed specifically with LEDs permanently installed. The shape, size, styling, lifetime and efficacy of a new LED fixture will be more appealing. LEDs allow a lot more flexibility in the design of the fixture due to its small size and the heat dissipation gets conducted out the back of LED instead of radiate out the front, like traditional incandescent technology. The implementation of standards in LED lighting will also help drive adoption with quality products. The lack of education and poorly designed products in the marketplace will cause LEDs to adopt slowly in long lifetime expected applications.

  10. Werner Mashig
    April 28, 2011

    Wattage may have been an acceptable way to define the amount of light being used in the traditional world. For example, as a rule of thumb incandescent and halogen technology has an efficacy of 10-15 lumens/watt and the technology isnt dramatically getting better. However, when using LEDs you have to define the amount of light you need by lumens. Every LED manufacturer and every led lighting design has different types of leds with different efficacies. You may see that some manufacturers have leds in the 50 lumens per watt range and some in the 160 lumens per watt range. If you happen to define light in wattage, then I think the manufacturer with the greater technology is at a significant disadvantage. This happens with different design scenerios as well. An LED may be 100 lumens per watt at 350mA (~1 watt) however the same led can be 80 lumens/watt at 700mA (~2.5 watts). This doesnt correlate as the same amount of light per watt. It is very important to analyse your system and figure out how much light you need on your target to assure you are using the right LED, the right quantity of leds and the proper surrounding components to design around it.

  11. tdalton335
    April 28, 2011

    I agree Werner that the thermal management is a key component of the process, and often the source of problems in the field when rigor isn't applied in development.  Heat sink and TIM selection is important on the luminaire side, and with higher lumen outputs some reliable form or air movement (like Nuventix SynJet) achieves high brightness and reliability in a smaller form factor…

    Himanshu the answer is yes to your question- you can definitely see inexpensive LED lamps outperform incandescents- they'll probably last longer and of course burn less energy but the tradeoffs of color temperature/quality and lifetime are variable and often not demonstrated as advertised.  Since we're in the “infant” phase of the SSL maturity curve, we'll see a lot of products that turn people off in the marketplace- which is why its wise for all of us in the industry to push for quality/standards that don' t pollute the market perception as the growth inevitably happens in coming years…

  12. Ms. Daisy
    April 28, 2011

    Lifelonglights

    Thank you for this quick tutorial!

  13. Taimoor Zubar
    April 29, 2011

    I am a big fan of LED based lighting. I think a great benefit of these comes with low maintenance costs. With traditional bulbs and tube-lights, the entire light or the bulb has to be replaced, whereas, with LED based lighting, only the faulty LED can be replaced. I think LEDs will definitely take on the future.

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