Watt to Lumen conversion

[swordfish2]

You can't. They measure two different things.

ok, but we cannot even compare these? something like
100 lumens is greater than 100 candles? anything like that?

 

[HKJ]

Ok, how can we convert lumens to candles ? seriously i don know this.

candelas is lm/st, i.e. "lumens" in a specific direction, to convert between candelas and lumens your need a radiation diagram, showing the radiation in every direction.

 

[Marduke]

ok, but we cannot even compare these? something like
100 lumens is greater than 100 candles? anything like that?

No, you cannot. Lumens is a measure of total output, where candles/lux is a measure of throw.

 

[TranceAddict]

The lumen (symbol: lm) is the SI unit of luminous flux, a measure of the perceived power of light. Luminous flux differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. The lumen is defined in relation to the candela by
1 lm = 1 cd·sr = 1 lx·m2reference: http://en.wikipedia.org/wiki/Lumen_(unit)

sorry my bad, lumen is a derived unit from candela, candela itself is base fundamental unit.

 

[mdocod]

I think the answer that the OP was after was something more along the lines of how to make a comparison when there are packages hanging on the shelf at target with different "wattage" listed on them.

The important point to take away from this, considering the motivations of the OP, is that, wattage on a package has very little meaning about how good or how bright or how useful a flashlight is going to be.

There are Modern flashlights that use ~2W of electrical energy, that perform as well as flashlights that use 5W from just a couple years ago. And there are still plenty of flashlights out there on the market that are using older emitter technology still... A Modern 1W Cree flashlight can outperform the older 3W Luxeon flashlights. The difference is quite amazing. Not just in total output, but the modern cree does a lot better as far as having a wider color spectrum.

The best way to compare is to look at how the flashlight performs when tested by reviewers who have the means of comparing runtime and output of various flashlights.

Many of the flashlight manufactures that are targeting CPF type audiences as their primary customers, have completely stopped listing watts, as it's often meaningless. Some of them have even stopped advertising lumens, instead, they just list the type of emitter used, and how much current the driver is set to run across the LED. From that we know what "class" of output the flashlight is in. Exact lumen figures are meaningless in actual use. Beam shape and color spectrum are often more important factors when comparing lights that are in the same ballpark of lumens.

Eric

 

[swordfish2]

mdocod, well said.

 

[Bolek]

Hey guys,

I found a conversion that said 1 lumen = 0.0003Watts. Surely this is wrong?

You can buy a 3Watt flashlight, which has an output of 65L, so is there anyway to compare the 2 values?

Stuart

This means that the max efficiency is 3333.33 lm/W. We have way to improove !
In other words if I filter only visible light from a 3333 ln torch I'll get 1W (for heatin e.g.)

 

[Swedpat]

I understand that it's true that watts MAINLY is marketing when it comes to flashlights in the ordinary store or supermarket. "1W, 3W or 5W-LED" says practically nothing to people, neither me, when I look at the package.
So good that the serious flashlight manufacturers and dealers don't use watts as a selling argument!

 

[tanmoy88]

That may be correct at some specific color, but:
Lumen is defined according to the eyes sensitivity, i.e. the watt<->lumen conversion is depend on the color of the light. One extreme is UV/IR light, your can have lots of watts in it, but the lumens are 0, because we can not see it.

And with flashlights (and anything else), your can not expect a 100% conversion, a lot of energy is wasted in heat.
Some typical values are:
incan: 5-30 lumen/watt
led: 60-100 lumen/watt

incan will have improved efficiency when really hot, i.e. very white light.
led will best efficiency at low output.

I have a 3watt led torch which says 140 lumen, is that correct?