Why can't they make a big LED?

[beowulff]

BTW, the MOST energy-efficient common light source is the lowly low-pressure Sodium vapor lamp. The yellow street lights.

[GusNSpot]

@beowulff

BTW, the MOST energy-efficient common light source is the lowly low-pressure Sodium vapor lamp. The yellow street lights.

And the car sales lot across the street are death to pilots making approaches at night in foggy or low visibility conditions at the airport.

[Q.E.D]

@beowulff

BTW, the MOST energy-efficient common light source is the lowly low-pressure Sodium vapor lamp. The yellow street lights.

Monochromatic LEDs are still more efficient. Your previous cite mentions white LEDs; these are relatively inefficient because the phgosphors used to create the white light absorb a lot of the excitation energy, converting it to heat.

[CalMeacham]

:
Originally Posted by beowulff
BTW, the MOST energy-efficient common light source is the lowly low-pressure Sodium vapor lamp. The yellow street lights.

Monochromatic LEDs are still more efficient. Your previous cite mentions white LEDs; these are relatively inefficient because the phgosphors used to create the white light absorb a lot of the excitation energy, converting it to heat.

I think you’re talking about different things. beowull is referencing pages on lighting, where he’s trying to illuminate a room with user-friendly light. QED is talking about efficiency under any lighting circumstances, even though your non-darkroom worker, or non-astronomy type, or non-movie-sub-command-room person wouldn’t be very happy in a red room.

[Ludovic]

@Mangetout

This is essentially the same question kids ask when you make cookies, isn’t it? - Why don’t we make one really big one?

Many years B.C. (Before Calmonella ) the question was more like "Why don’t we just eat the batter – the stuff you lick from the stirringspoon :eek: is much tastier than the cookedie

[beowulff]

If you really want the ultimate in monochromatic efficiency, look at the VCSEL:

Recent documents | page 1 of 4 | Light Reading

Supposedly up to 51% efficient, as compared the <10% for an LED.

[CalMeacham]

If you really want the ultimate in monochromatic efficiency, look at the VCSEL:
http://www.lightreading.com/document.asp?doc_id=133802
Supposedly up to 51% efficient, as compared the <10% for an LED.

A VCSEL is a laser. Laser diodes have lower efficiencies than LEDs, in general. I can’t believe a VCSEL has a higher efficiency than an ordinary LED.

And — less than 10% for an LED? That HAS to be wrong. LEDs aren’t that inefficient.
I’ve been looking for a measure of true efficiency on the web (energy or power in the form of light out vs. electrical energy or power in), but it’s proving remarkably slippery. Most people seem to want this in terms of lumens or candelas out vs. power in.

[CalMeacham]

But here’s an off-the-shelf LED with 42% “Wallplug efficiency”:

UPDATE 11/4/2004 - Cree has announced on 10/12/2004 blue LED dice (chips) that produce 27 milliwatts of blue light having a dominant wavelength of 460 nm at 20 mA with a typical forward voltage drop of 3.2 volts. This works out to a conversion efficiency or “wallplug efficiency” of 42 percent! This is an announcement of sampling of chips that efficient, and commercial production of ones that produce 24 milliwatts at 20 mA (37.5% efficiency).

Relevant press release: HERE.

Relevant datasheet: HERE.

http://members.misty.com/don/led.html

[scr4]

@Q.E.D.

Monochromatic LEDs are still more efficient.

Which ones? The orange-red CREE XR is only 49 lumens at 350 mA, which works out to 62 lumen/W. The green one is even worse at 42 lumen/W. Are there any mohochromatic LEDs that do much better?

[Sunspace]

@beowulff

Generally, the light output isn’t rated in Watts, but rather Candela or Lumens. I’ve seen single-package LEDs rated up to 1200 Lumens, which is brighter than a 60W incandescent bulb: Powerful Little Light: LED With 1,000 Lumens

From Wikipedia on the lux:

Like all photometric units, the lux has a corresponding “radiometric” unit. The difference between any photometric unit and its corresponding radiometric unit is that radiometric units are based on physical power, with all wavelengths being weighted equally, while photometric units take into account the fact that the eye is more sensitive to some wavelengths than others, and accordingly every wavelength is given a different weight. The weighting factor is known as the luminosity function.

The lux is one lumen/meter[sup]2[/sup], and the corresponding radiometric unit, which has no special name, is the watt/meter[sup]2[/sup]. There is no single conversion factor between lux and watt/meter[sup]2[/sup]; there is a different conversion factor for every wavelength, and it is not possible to make a conversion unless one knows the spectral composition of the light.

I was talking radiometric units: total power emitted. I guess I’m used to that because I’m used to dealing with passive-solar heating, not lighting, so much. But it’s good to know about.

[Sockmunkey]

So how long do you guys think it will be before the old “hey-I-have-an-idea” type lightbulbs aren’t made anywhere anymore and the ghost of Edison pitches a hissy fit?

[Mangetout]

@Sockmunkey

So how long do you guys think it will be before the old “hey-I-have-an-idea” type lightbulbs aren’t made anywhere anymore and the ghost of Edison pitches a hissy fit?

I don’t know - there are already groups campaigning for their banishment -arguing that you can get CFLs to fit anything now (which just isn’t true - they’re better than they used to be, but there are still some types of lamp into which they just won’t fit properly).

[CalMeacham]

I just lit up an awesomely bright LED yesterday. It also got amazingly hot (or not so amazing, considering how bright it waas) – it was able to melt the solder on its leads. THAT’LL teach me to consider LEDs as :cool" light sources.

[beowulff]

@CalMeacham

I just lit up an awesomely bright LED yesterday. It also got amazingly hot (or not so amazing, considering how bright it waas) – it was able to melt the solder on its leads. THAT’LL teach me to consider LEDs as :cool" light sources.

Yes, it’s easy to forget that a 5W LED is actually dissipating 5W - as much as a nightlight.

[Billdo]

@Sockmunkey

So how long do you guys think it will be before the old “hey-I-have-an-idea” type lightbulbs aren’t made anywhere anymore and the ghost of Edison pitches a hissy fit?

How about 2012 in the US under the recently passed energy law.

[beowulff]

@Billdo

How about 2012 in the US under the recently passed energy law.

There are technologies that could possibly allow tungsten incandescent lamps to exceed these standards: Tungsten Photonic Lattice Changes Heat To Light; Cool Tungsten Light Bulb May Be Possible | ScienceDaily
We’ll see.