Calculation of light on a surface

1. May 18, 2012

ajpapia

I am looking for a formula to calculate the amount of light on a surface in lux if I know the distance the light fixture is above the surface and the lumen output of the LED bulb.

2. May 18, 2012

Whovian

Depends on the shape of the surface. If you want this to work for almost any sort of surface, look into multivariable calculus. If you want a flat plane, the case is a bit simpler.

3. May 18, 2012

ajpapia

The surface would be flat such as a desk. I am looking for a formula to calculate the amount of light on the desk surface from an overhead task light.

4. May 18, 2012

Whovian

Okay. Is the light in the centre of the desk, and do you want it in terms of the lengths of the sides of the desk?

5. May 18, 2012

ajpapia

The light is in the center of the desk and it has two fluorescent tubes, 24" long. The desk size is 30" deep by 48" long and the light is located 48" above the surface.

6. May 18, 2012

Bob S

See the Table in http://en.wikipedia.org/wiki/Lux. The recommended light level is about 50 lux for a living room, to 300-500 lux for an office hallway.

Here is the conversion from lux to watts per m2:
"The peak of the luminosity function is at 555 nm (green); the eye's visual system is more sensitive to light of this wavelength than any other. For monochromatic light of this wavelength, the irradiance needed to make one lux is minimum, at 1.464 mW/m2."

7. May 21, 2012

ajpapia

Thanks for the replies, but I am still looking for the formula to calculate the amount of light on a surface. Is there some reference material I could check out on this topic?

8. May 21, 2012

Staff: Mentor

1 lux = 1 lumen/mÂ². So the formula is simply to take the lumens doing the illuminating and divide them by the area being illuminated.

Of course, this assumes uniform illumination within the target area and no "spillover" illumination outside the target area. Neither of which are likely to be valid assumptions.