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

Re:well, likely not.

[farquharsoncraig]

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

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

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