Do red LEDs use less power?

Will_

Active member
Joined
Oct 17, 2005
Messages
36
Location
Arizona
I heard that the red ones use a lot less battery than white ones. If this is true, then red LEDs are a lot more efficent than white ones with a red filter.
 

TorchMan

Well-known member
Joined
Aug 7, 2005
Messages
805
Location
Texas
Yes, it's my understanding that red LEDs use less power than white, and are more efficient than a white with red filter.
 

Lynx_Arc

Well-known member
Joined
Oct 1, 2004
Messages
10,754
Location
Tulsa,OK
red leds are driven at about the same current and similar brightness I think but the considerably lower Vf makes for a lot less power use.... probably about 1/3 less or so.
 

jtr1962

Well-known member
Joined
Nov 22, 2003
Messages
6,220
Location
Flushing, NY
Reds are certainly more efficient than whites with a red filter, probably by a factor a three or four. However, in terms of overall efficiency emitting visible light whites are actually better, although not by much. I recently measured some 9000 mcd reds at roughly 40 lm/W. The same company now has 11,000 mcd with a similar beam angle which should manage in the high 40s. The better 5mm whites are in the 60 to 75 lm/W range according to my tests. However, that doesn't tell the whole story. In terms of converting energy to light the best whites are about 20% efficient while the best reds are probably around 35% or so. The lumens per watt are less simply because our eyes are less sensitive to narrowband red light than to white.

Yes, at 20 mA drive current reds use less because their Vf is in the 1.9 to 2.1 volt area instead of the 3.2 to 3.6V typical of whites.
 

scaredofthedark

Well-known member
Joined
Sep 11, 2005
Messages
260
Location
TX
jtr1962 said:
Reds are certainly more efficient than whites with a red filter, probably by a factor a three or four. However, in terms of overall efficiency emitting visible light whites are actually better, although not by much. I recently measured some 9000 mcd reds at roughly 40 lm/W. The same company now has 11,000 mcd with a similar beam angle which should manage in the high 40s. The better 5mm whites are in the 60 to 75 lm/W range according to my tests. However, that doesn't tell the whole story. In terms of converting energy to light the best whites are about 20% efficient while the best reds are probably around 35% or so. The lumens per watt are less simply because our eyes are less sensitive to narrowband red light than to white.

Yes, at 20 mA drive current reds use less because their Vf is in the 1.9 to 2.1 volt area instead of the 3.2 to 3.6V typical of whites.

narrow band red light??? what does that mean?
i thought red has the longest wavelengths in the visible spectrum
 

cratz2

Well-known member
Joined
Apr 6, 2003
Messages
3,947
Location
Central IN
I think by narrow band, he is referring to the fact that it isn't a wide range such as white but only a limited range of color.

I tell you, I have a Garrity Stainless pen light with about a 7,000 MCD (might be a 9,000) LED into that I put two, we'll say, 80% fresh NiMH cells into and it's still as bright today as when I put it together a year ago... Granted, I don't use it every day, but it seems to last and last and last.
 

PhotonWrangler

Well-known member
Joined
Oct 19, 2003
Messages
13,046
Location
In a handbasket
Narrowband = monochromatic. For instance, one of the reasons why LED traffic lights stand out among the visual clutter of a busy intersection is that their color is fairly "pure" or monochromatic, something that we usually don't see in nature. An incandescent red traffic light doesn't stand out as much, partly because the "red" actually contains many wavelengths of reddish-orangeish colors.

When you look at a spec sheet for an LED (other than white), you'll see a dominant wavelength specified. While the LED may put out a few other wavelengths very close to the dominant one, they're greatly attenuated. LEDs are extremely efficient compared to incandescents in producing a particular color because of this.
 
Top