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How effective are LEDs really?
2015-03-03 09:15:59

5 myths about LED lighting

LED lighting is touted as the wave of the future, the great white hope of energy efficient lighting.
But it’s a topic that many lighting showroom owners sheepishly admit they’re still in the dark about.
So how does LED lighting really work? When will it be revolutionizing the lighting industry, and how can you be prepared?

Here, Dave Simon, President of the Troy, Michigan-based LED lighting manufacturer ilumisys, gets to the bottom of five common LED lighting myths.

Myth 1: LEDs don’t use any power, or they are at least 10 times more efficient than any other kind of lighting.

Fact: “LEDs are about 15 percent more efficient than fluorescent lights, and six times as efficient as incandescent — and rapidly improving.

“LEDs are on an impressive development path. In just the past year, we have seen commercially available dies move from 65 lumens per watt to over 90 lumens per watt. Within the next five to seven years, there seems to be a clear path past 150 lumens per watt and a reasonable expectation of approaching 200 lumens per watt.  This represents a tremendous opportunity to provide a real alternative to fluorescent lighting.

“Note that these LED efficiencies then need to be combined with power conversion circuitry efficiencies, optical efficiencies, etc., to come up with a total LED lighting system efficacy. For example, a product using a 90 lumens per watt LED may have a total system efficiency of 60 lumens per watt when everything is accounted for. Unfortunately, it is common today to find an LED product advertising well over 100 lumens per watt, leading to buyer disappointment.”

Myth 2: LEDs last forever.

Fact: “With proper thermal design, LEDs can achieve 60,000+ hours of life while maintaining 70 percent of original light output.

“The number one reason that properly manufactured LEDs fail prematurely is overheating. Note that we say “properly manufactured” because not all LEDs are the same, and there are certainly a lot of very low-quality products out there. However, given a top-shelf LED product, it is vitally important to manage the junction temperatures in order to maximize the lifetime.

“The failure criteria on LEDs has been established as the output equal to 70 percent of the rated light at the original rated power draw. This criteria recognizes the failure mode of LEDs as being one of a slow fade versus a sudden burn-out.  This offers some good safety advantages in that a dim light is usually preferable to no light at all.

“At ilumisys we use a rigorous combination of computational fluid dynamics (CFD) and testing to develop our mechanical designs in support of LEDs.”

Myth 3: LEDs don’t give off any heat.

Fact: “LEDs don’t give off radiant heat, but they do need to get rid of conductive heat in order to achieve long life.

“You can hold your hand in front of a bank of LEDs and not feel any appreciable heat. However, touch the back of the circuit board or heat sink and you will certainly feel quite a bit of heat. Even though LEDs are many times more efficient than incandescent lighting, the overall efficiency is still quite low. Energy that goes into a light source can either make light to create heat, to effect a chemical change or convert to mechanical motion. Lacking a chemical change or mechanical movement, what doesn’t come out as light needs to come out as heat.

“The need to dissipate conductive heat leads to the need for proper thermal design, which is the reason that many LED products have somewhat elaborate heat sinks attached to them. As LEDs become more efficient, more light will be put out per unit of energy, thus there will be less heat and less need for the intensive heat sinks found in today’s well-designed LED products. As LEDs become more efficient, the thermo-mechanical design becomes simpler and the amount of material used in LED products is reduced.”

Myth 4: LEDs are really cheap.

Fact: “LEDs are really expensive — and getting cheaper at an impressive rate.

“We have seen the cost of LEDs, as measured in dollars per lumen, come down 50 percent in the last year and a half. That still leaves LEDs many times more expensive than incandescent and fluorescent. In the next four years, though, we will see another 80 percent price reduction in LEDs. At that point the price/performance of LEDs will provide payback periods of well under two years, even against fluorescent lighting.”

Myth 5: LEDs can only produce blue light.

Fact: “White-light LEDs can produce very nice color temperatures ranging from 2,700K to 6,500K, with color rendering index (CRI) numbers of 90+.

“The ability to control light to very specific spectra is unique to LEDs and the consistency of the light output has improved markedly in the past few years. There are some undesirable, blue-yellow LEDs on the market — but products from the top suppliers provide wonderful light quality. The best suppliers can provide a full range of spectrographic data — insist on it.”

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