Here is the third part of Ed Rodriguez's series "What You Should Know About HBLEDs -- and Nobody Will Tell You." This one is titled "From Theory to Practice." -- Ed.
It is well recognized in the lighting industry that fluorescent lamps can often equal the efficacy (lumens per watt) of the very best LEDs and are dramatically lower in cost. But the LPW figures for LEDs on manufacturers' data sheets only tell half the story. If an LED is rated to deliver 120 LPW when driven with 350 mA at a junction temperature of 25°C, it is unlikely to have what is called a "delivered" LPW of more than 80 to 90 after all system losses for temperature effects, optics, power supplies, and current drop-off are factored in.
Meanwhile, LEDs' arch-nemesis, fluorescent lamps, can deliver very comparable performance at a cost that's less than one-fifth the cost of LED lamps, and still last 6 to 10 times longer than incandescent bulbs. This means that, barring any technical breakthroughs or market disruptions, fluorescents will dominate many areas of wide-area lighting for a few more years. For our purposes, wide-area lighting serves applications that don't require light to be focused or directed toward specific areas and can include certain down-lights and high-bay warehousing lighting.
These hard realities mean that LEDs and fluorescents are likely to coexist quite a while longer, each doing what it does best. That said, LEDs will displace their mercury-laden cousins more quickly in applications where fluorescents have difficulty, such as operating in temperatures below 32°F, performing full-range dimming, operating without noise or vibration, or being constantly subjected to frequent on/off cycles. LEDs will also quickly edge out fluorescents in locations where breakage is an issue.
Read the rest of Part 3 at EDN.