I have a quote of 1 watt to 1.2 lux; can anyone confirm?
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Re: lux to watt
I dont think you can make a direct conversion between lux and watt.
One lux is defined as an illumination of one lumen per square meter or 0.0001 phot.
One lumen represents the total flux of light emitted, equal to the intensity in candelas multiplied by the solid angle in steradians (1/(4·pi) of a sphere) into which the light is emitted.

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Re: lux to watt
100 lumens per watt is a high efficiency source.
http://www.luminus.com/products/data..._Datasheet.pdf
Here's a benchmark
"Grand Sands All Season Beach Volleyball is the first indoor / outdoor sand facility in Ohio. The recently opened five outdoor courts are illuminated with the Courtsider XL system from LSI Industries. Using four fixtures [2 lamps per fixture] per court with 750 watt pulse start metal halide lamps, the lighting system provides a maintained light level of 40 footcandles. Mounted at 25’, the Courtsider XL fixtures uniformly light the courts with minimal spill light outside of the court boundaries."
and Lithonia Lighting is pretty good about answering questions about their fixtures.
Here's a graph
http://www.venturelighting.com/TechC...TechIntro.html
and some basics
http://www.westsidesystems.com/rays.htmlLast edited by HerrWarum; 08252011, 08:35 AM.
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Re: lux to watt
This may help, or not. . .
"How many lumens in a watt of white light?
The answer depends on what you call "white light". I give many options below for "white light" along with lumens per watt thereof. This would be the overall luminous efficacy of a hypothetical light source that is 100% efficient at converting input energy (typically electrical energy) to light of one of the following definitions, with zero input energy becoming anything else such as heat or radiation outside the relevant definition of "white light".
Equal power per unit wavelength from 377.5762.5 nm  189.6 lumens/watt
Equal power per unit wavelength from 380 to 760 nm  192 lumens/watt
Equal power per unit wavelength from 400 to 700 nm  243 lumens/watt
Equal power per unit wavelength from 422.5 to 692.5 nm,which has color of a 5270 K blackbody: 264.5 lumens/watt.
400700 nm portions of blackbody radiation at a few color temperatures:
3000 K: 256 lumens/watt
3400 K: 262 lumens/watt
36004100 K: 263 lumens/watt, within 1 lumen/watt.
4500 K: 261 lumens/watt
5000 K: 258 lumens/watt
5500 K: 254 lumens/watt
6500 K: 246 lumens/watt
Trichromatic white / "white" achieved with 611 nm, 544 nm, and 450 nm:
4100K approximation  397.5 lumens/watt
3500K approximation  401.4 lumens/watt
Dichromatic "white":
4100K approximation with 450 nm blue and 573 nm greenish yellow: 478 lumens/watt.
3500K approximation with 450 nm blue and 576 nm yellow: 495 lumens/watt."
and
"a typical incandescent light bulb has a luminous efficiency of only about 2%."
Lux is a measure of illuminance, which is the luminous flux that is incident per unit area.
And the intensity of light falls off as the distance squared.Last edited by HerrWarum; 08262011, 09:28 AM.
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Re: lux to watt
Here's a conversion using sunlight, 100,000 lux at the earth's surface, as a standard.
A spotlight has an intensity of 5,000,000 candles [not 'candlepower' because it's not power]. The intensity decreases as the square of the distance, so for the spotlight circle to be as bright as the sunlight it must be R = sq. rt (5,000,000/100,000) = 7.07 meters from the illuminated surface.
You can then vary the distance from the light to the surface to match the sun's intensity and then use the formula to figure out the light's intensity in candles.
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