Solid State of Affairs

A Rensselaer Polytechnic Institute lighting design and research specialist talks about todays LED product quality.
Residential Lighting: Whats your assessment of LED products? Jean Paul Freyssinier: We see products that are very expensive and some very inexpensive, all with varying qualities. Unfortunately, there is not enough information in the market.

RL: What are some of your recommendations?
JPF: Our ASSIST Recommends guidelines are useful for trying to understand what questions to ask. Our first recommendation was the definition of LED light, defining how to measure and characterize LED life. Its the origin of what is now known as L70 —70 percent lumen maintenance for life. We have another document on LED engines —how to test LED engines.

RL: How do LED engines perform?
JPF: The industry has done very well in increasing efficacy, or the lumens per watt. Many LEDs produce 100 to 110 lumens per watt. The bulk of the market ranges between 40 and 60 lumens per watt, but LED life has increased as well.

RL: What is the average LED life?
JPF: Im not surprised when a manufacturer says the life of its LEDs is 20,000 to 35,000 hours. But this is under specific conditions. You can have a good LED, a good driver and a well - designed system, but the wrong application. A downlight may be designed to operate in open air as a pendant. Put a variation of that product in a recessed can application, where the temperature is higher, and its life will be significantly lowered There is some misunderstanding in the industry. When a system is rated at 50,000 hours, people need to keep in mind that that is a very long time. Were talking about at least seven years of 24/7 use. Other things can fail. The diffusers can become brittle and break before the LED fails.

RL: Consumers want long life, right?
JPF: Actually, many residential users say they dont care for 50,000 hours. They dont change their incandescent bulbs but once a year or year - and - a - half. So, there is no reason to oversell products. If you offer a lower cost for 10,000 hours, instead of 50,000 hours, I think people will be equally happy. Many dont want to overpay for a product that is going to last 15 years. Theyd prefer to buy something that will last five years and use the extra money on something else.

RL: Are drivers a limiting factor?
JPF: The life of the luminaire is defined by the weakest link, which can be the driver. Most drivers have capacitors, and you can have a capacitor rated at 2,000 hours or 50,000 hours. If the capacitor is rated at 2,000 hours, but its always operating in a cool condition, its going to last a long time. So, there is always a tradeoff between size, cost, efficiency and application.

RL: Is anybody trying to certify LEDs for quality?
JPF: In a way, Energy Star® is trying to do that by qualifying products with a minimum rated life of "X." I forget the numbers but, depending on the application, they say 20,000 or 35,000 and so on. The problem is that the industry is still learning. We dont have any real - life history. Everything is based on prediction.

RL: What are you working on at the Lighting Research Center?
JPF: Most of what we do is understand the performance of components —LEDs, drivers, optics —by themselves. Now, we are looking at coming up with recommendations for life predictions on complete systems. We have had products in the rack for a couple of months, and were including more conditions. Probably within a year well have preliminary recommendations on what to look for.