The End Of The Light Bulb?

sdmonroe wrote to mention an MSNBC article discussing the likely eventual replacement of common light bulbs by LEDs. That replacement is likely to come quicker thanks to an accidental discovery announced this week. From the article: "Michael Bowers, a graduate student at Vanderbilt University, was just trying to make really small quantum dots, which are crystals generally only a few nanometers big. ... When you shine a light on quantum dots or apply electricity to them, they react by producing their own light, normally a bright, vibrant color. But when Bowers shined a laser on his batch of dots, something unexpected happened. 'I was surprised when a white glow covered the table,' Bowers said. 'The quantum dots were supposed to emit blue light, but instead they were giving off a beautiful white glow.'"

Comments

From the FAQ on LEDs

[jkind]

Answer: there are several obvious advantages LEDs have over traditional incandescent light bulbs, they are as follows:
Low power consumption - energy saving,
Long lasting,
Cold lighting,
Ruggedness,
Small size and weight,
Fast switch times,
Simple to use.
This is from the FAQ, but it doesn't list any disadvantages..
anyone care to share?

Re:From the FAQ on LEDs

[Rob the Bold]

Some Disadvantages:

Like Fluorescent, requires supporting circuitry -- doesn't plug directly into AC wiring.
Cost (initial investment)
Harder to dim -- can't use simple rheostat
Flicker (if using less than 100% on time)

I don't have anything against LED lighting, and none of these disadvantages are insurmountable. Indeed, these could be viewed as business opportunities instead. Most of the disadvantages are shared with fluorescents, and adequate solutions already exist there. I know a guy who lights his whole off-grid house with LEDs (using low voltage DC wiring). I particularly like the possibility of creating variable color lighting with LEDs, emulating daylight, sunlight, tungsten or whatever.

Re:It's about damn time!

[joostje]

Considering that the average lightbulb creates more heat than light, this is great!
As lightbulbs create about 95% to 98% heat (the rest is light), and modern LEDs about 85% to 96% heat, the LEDs still create more heat than light.

reference

LED efficiency versus Compact Fluorescents

[lancejjj]

This could be a big advance for LEDs. But as of now, commercially available LEDs do NOT produce as many lumens per watt as Compact Fluorescent Light bulbs (CFLs.) Of course, this new LED discovery may improve LED efficiency to the point where they exceed CFL efficiency. We'll have to wait and see.

CFLs are inexpensive and readily available today. CFLs have a long life, and they save a ton of energy when compared to traditional light bulbs. Even more importantly, they don't suck like the CFLs of a few years ago that had a noticeable/painful "warm up" time.

I save quite a bit off of my energy bill by using CFLs. They really cut down on electricity consumption, and I've never had one "burn out" on me. Ever. Yet.

Re:well, likely not.

[way2trivial]

alright, it has the white light, and none of the 'rest' of the spectrum, which apparently attracts bugs.
but yes, a narrow spectrum of white, I found a good picture here
http://www.truesun.com/Litetube.htm

roll down to where there are three bulb types listed.

note the incandescent bulb rolls up from blue to red
note the fluroscent has three spikes of blue, yellow and red

the missing bits, including the missing UV and IR at the ends, include whatever attract bugs.

so yes- a narrow band of white light......

Re:well, likely not.

[farquharsoncraig]

http://exploration.vanderbilt.edu/images/news/arti cle_main/quantumdot_led_5.jpg

Current LEDs are not there yet

[The Optimizer]

I just finished converting the lighting in my house to save energy, and learned a few things in the process. Most of the incandescent bulbs were replaced with compact fluorescents, but I did install 4 LED light bulbs in one application.

The current generation of compact fluorescent bulbs has come a long way from the ones I remember 10-20 years ago. They don't have the flicker or startup problem anymore, and they are available in a variety of color temperatures from 2700 degrees (yellowish, comparable to incandescent) to 6100 degrees (white, sterile). For the same light output (lumens), energy consumption is normally 22% to 27% of the incandescent bulbs they replace. They very slightly in things like color and wattage depending on the manufacturer.

Nobody who has visited my home has yet noticed the difference.

Since you can find common CF bulbs sizes for under $2 per unit (try Sams Club, etc), and they should last 4 to 8 times as long as an incandescent, the economic case is pretty sound even before factoring in the energy savings.

I replaced 4x 7.5 watt bulbs with LED bulbs and noticed a few things. The LED bulb itself is about twice as large, and as others have mentioned, the light emitted is an eerie blue-white light. You defiantly notice it. These bulbs consume 0.8 watts and produce an output pretty close to the 7.5 watt bulbs they replaced, though I could not find the output in lumens for either bulb anywhere. They were about $7 a bulb, and are rated to last 100K hours, or about 50 times as long the bulbs they replaced. Since the bulb is actually made of up 18 individual LEDs inside, I believe the rating is for the mean time until 50% of the LEDs are no longer functioning.

After converting 152 of 160 bulbs in my home, my electric bill happy.

no, it is NOT a contradiciton

[way2trivial]

I can make white light by emitting everything from UV to IR

or I can combine a 3 beams each of a very precise wavelength of red green and blue, and end up with WHITE.

a narrow spectrum of white.
very perception based.. I may see it as pure white, you may be more sensitive to one of the three, and therefore see it as green or blue or red tinged.

a bug may not see it at all.

Re:no, it is NOT a contradiciton

[dgatwood]

That's not true. At any brightness level, an equal combination of red, green, and blue will be perceived as white. It doesn't have to be "an overbrightness".

There are an infinte number of white light spectra. You seem to be defining it very narrowly as an incandescent white, but that is not the standard definition of the term.

Re:The greatest discoveries...

[B-a-Z.nl]

Let's quote the source on that now shall we?
Isaac Asimov
"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny...'"
http://en.wikiquote.org/wiki/Isaac_Asimov

Perhaps, but...

[msauve]

that only applies to the perception of the emitted light itself. However, objects illuminated by such a light source may appear to be significantly different in color than they would under a broad spectrum white light, since they may reflect light in narrow bands not matching those of the source.

Combining narrow spectrum RGB sources can work to produce whatever perceived color you want, as in a display. It does not work for all reflective lighting needs, so a solid state broad spectrum source still fills a need.

Re:It's about damn time!

[syukton]

Something interesting and useful to know is that the other reply you received to your post is totally incorrect.

First, LEDs are current driven, not voltage driven. The voltage difference between + and - determines the amount of current the device will consume, but if you can regulate the current you can run the device at 100V no sweat. You will of course need to dissipate any additional heat (usually in the device you're using to do the current limiting, sometimes a resistor, sometimes a more exotic circuit) created, but the very important thing to understand about LEDs is that their current absolutely determines their light output after you surpass a certain threshold voltage.

The relationship between the +/- voltage difference and the amount of current consumed is not the same for every kind of LED. LEDs require different chemistry in order to produce different colors, and this makes them have differing performance characteristics.

And another thing to consider is how the LEDs are packaged. Some 8mm packages have 4 chips inside and their rated light output is measured at a regulated input current of 80mA and not 20mA as for most single-chip devices. Also, some blue devices consume 30mA while reds only consume 20mA. Again, this depends on the chemistry. Now, also, taking packaging into consideration, a Luxeon device from Lumileds and a BL-3000 from Lamina Ceramics have totally different performance characteristics because of their chemistry, construction, packaging, and so forth.

You have two choices: Limit the voltage so that the device does not consume as much current, or limit your current and ensure that the voltage simply exceeds the maximum. Ultimately you need to regulate the current because the amount of current consumed (taking into consideration the device's ultimate efficiency) is directly proportional to the amount of heat generated in the chip itself.

You see, LEDs don't generate heat in their light path (radiant infrared travelling in parallel with the visible light, like the "heat" of the sun or a candle), but the chip itself does get rather hot, and if that heat isn't dissipated the LED chip will become physically damaged. Some of the materials used have melting points below 120 degrees, a temperature easily achieved by an LED not properly heatsinked.

So here's some tips: When you make LED boards (whether addressable matrices or simple blinky lights) you want to use a metal-core PCB or leave a portion of the LED's leads exposed in order to help dissipate the heat generated at the chip core and ensure longer chip life. LEDs don't just "burn out" one day, they will get dimmer slowly over time, and you can maximize that length of time by running them at less than their rated current, by cooling them actively or passively, and by using PWM to modulate their output.

Don Klipstein maintains a good set of information about LEDs: http://members.misty.com/don/ledx.html