LED's everywhere
by TreeHugger 
on 04.18.05
Light emitting diodes (LED's) have been growing in power and finding new uses since 1993, when the blue LED was invented and could be mixed with red and green to make white light. They are still expensive, but last 50 times as long as a conventional bulb, and use a lot less power. However, white LED's are not as efficient as they might be, because almost half of the output is wasted, reflected inward by the phosphor that produces the visible output. This week, Scientists at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute announced a new advance that solves this problem.
According to the press release,
"We have developed a technology based on a new scattered photon extraction (SPE) method that will speed up the progress of solid-state lighting and help secure our nation's energy future," said Nadarajah Narendran, Ph.D., director of research at the LRC. "The new technology dramatically increases light output and efficacy of white LEDs, and could play a fundamental role in the evolution of white LEDs for lighting in homes and offices."
Lightbulb efficiency is measured by the number of lumens produced per watt of power. A conventional light bulb puts out 14 lm/w; a compact flourescent 60 lm/w. The SPE LED achieves 80 lm/w and they are aiming for 150lm/w- over 10 times the efficiency of current bulbs.
Many people prefer the colour balance of conventional incandescent bulbs, and like the fact that one can use a dimmer. Compact flourescents do not quite hit the right colour temperature and cannot be dimmed.
WIth LED's. we will be able to dial up not only the intensity but the colour balance- warmer, redder light for sunset dinner parties; cool and bright for working.
::Lighting Research Center by [LA]
Follow @TreeHugger on Twitter & get our headlines with @TH_rss!
Thirsty for more? Check out these related articles:
Um . . . yes, dimmable CFLs are available:
http://www.eere.energy.gov/consumerinfo/factsheets/ef2.html
http://www.google.com/search?q=dimmable+compact+fluorescent
Even LRC states the fact:
http://www.lrc.rpi.edu/programs/lighthealth/aarp/designers/lightingolderadults/choosingsources.asp
But there are very few reasons one would ever need to use a white LED. As you mention at the top of the article it's easy enough (and more flexible) to use a mixture of red, green, and blue LEDs.
For 120V systems: Dimmer devices are inherently energy consumptive, especially at the low end of the amp output range. They are also expensive Better to have a mixture of colored/white LED's that are clustered together in bulbs that are pre-programmed for multiple operations: e.g. each bulb can perform as a dinner light, romantic dinner light,night-reading, day-reading, plants, etc. On the wall switch, one toggle on defaults to full bright nighttime reading, toggle on/off/on to the next config, etc. Bulb can be programmed for default with side dip-switch.
For 12V-24V DC systems: best to have the light fixture controlled wirelessly with remotes that can be accessed by a handheld device, with access distributed among homeowners cell phone, PDA, PC-on-internet, etc. This is good because DC voltage loss over line length is significant and switch wires provide a significant source of power loss. THis would also obviate a fair amount of copper.
i was assured by the seller of my dimmable cf bulb that it was specifically designed to use less energy as it was dimmed unlike most incandescent dimmers which actually use the same or more energy as they are turned down. perhaps he was lying, but i highly doubt it. are you absolutely sure of what you say, john?
Thanks to Ben for his correction and John for his defense, but since the piece was about LED's I did not check carefully on the CFL dimming issue.
My reference was to the actual dimming wall switch consuming more energy than a standard on/off toggle switch. That happens regardless of which kind of bulb is used. All voltage transformation processes consume some energy. Hence, my arguement was to have no volatage transformers at all to accomplish "dimming": e.g. in a cluster of 36 LED's, each is independently wired and can be programmed to run as part of a subgroup. Kind of like running a V6 engine on only 4 cylinders when at a stop sign or cruising at low speed.
interesting... is it a big difference in the switch? would having 36 switches (for example) be more energy efficient than one dimmer switch?
By using a programmable embedded processor instead of old-fashiibed hardware switches, recitfiers would direct the voltage to individual LED's based on software, not hardware. IF you look at one of the LED based traffic signs that tell you about upcoming conditions on the highway, its the same thing behind them.
I find that recent compact fluo bulbs (at least those that I buy -- there's probably a difference between brands) have a very nice light colour.
Those from a few years ago were pretty horrible, though.
Color mixing might get you the right color temperature, but things wouldn't necessarily always look right - the red, green, and blue LEDs each emit a fairly narrow range of wavelengths of light, so you'd have a lot of gaps in the spectrum, no matter what color temperature you were simulating. That's why phosphors are used in white LEDs (and flourescent bulbs): the broadband emission across the visible spectrum.