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# Convert lux to w/m2

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## Convert lux to w/m2

(OP)
Is there a formula to convert lighting of 1600 lux to W/m2? A customer says he has 1600 lux lighting. How can I convert 1600 lux to W/m2 for obtaining the cooling load from the lightning.

Thanks,

### RE: Convert lux to w/m2

mechanicblues
It appears that your question cannot be answered by a single conversion equation between lux and watt/meter2
The following is an excerpt from Reference.com

Relationship between illuminance and power

"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/meter2, and accordingly the corresponding radiometric unit, which has no special name, is the watt/meter2. There is no single conversion factor between lux and watt/meter2; 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.

At a monochromatic light wavelength of 555 nm, the green-colored wavelength to which the eye is most sensitive, the power needed to make one lumen is minimum, at 1.464 mW/m²; that is, the peak of the luminosity function is 683.002 lumens per watt. This means that for green light of this particular wavelength, one lumen = 1/683 watt. The luminosity function falls to zero in the infrared and ultraviolet wavelengths.

For a light source with mixed wavelengths, the number of lumens per watt can be calculated by means of the luminosity function. In order to appear reasonably "white," a light source cannot consist solely of the green light to which the eye is most sensitive, but must include a generous mixture of red and blue wavelengths to which it is much less sensitive.

This means that typical white (or whitish) light sources produce far fewer lumens per watt than the theoretical maximum of 683 lumens per watt. The ratio between the actual number of lumens per watt and the theoretical maximum is expressed as a percentage known as the luminous efficiency. For example, a typical incandescent light bulb has a luminous efficiency of only about 2%.

In reality, individual eyes vary in their luminosity functions. However, photometric units are precisely defined and precisely measurable. They are based on an agreed-upon standard luminosity function which is in fact based on the measurement of eyes and is reasonably close to the sensitivity"

### RE: Convert lux to w/m2

Or look at the lighting layout drawings and luminare schedule and do a takeoff?  Or if it is existing go to the premises.

### RE: Convert lux to w/m2

Your question doesn't quite make sense to me.  The cooling load is the wattage of the light.  The lumens is irrelevant to the first order.

However, if you really need to do the calculation, you should read:
http://en.wikipedia.org/wiki/Luminous_efficacy

Quartz halogen is about 16 lm/W

### RE: Convert lux to w/m2

(OP)
Thanks you all,

I have checked in the internet for an answer but could not find a satisfactory answer for it. After than I have sent it to this forum.

### RE: Convert lux to w/m2

Don't know if this will help, but lux to watts is like sound pressure to sound power.

The two are related, but room effect makes a big difference. A bright light in a dark walled room will result in the same lux as a weaker light in a light walled room.

Net result, there is no direct conversion between lux and watts.

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