I am using an LED as a point source for a school project. I have two questions in regards to the LED(s).

I know that light follows the inverse square law when measuring perceived brightness, but all sources I can find show examples of a round bulb light. Is there an altered version of the formula for LED’s that incorporates factors such as the fan angles?

Also, I will most likely be adding more LED’s to my project to increase the total lumens/lux. I’ve seen many people ask the question whether lumens will add in such a scenario. In theory they would but it wouldn’t be perceived that way. My question is; is there a formula/equation/calculation that can help me predict the lumens perceived by x number of LED’s, d inches apart from one another, measured at y feet away, with regard to joining and isolated parts of the fan angles of each LED.


If you want to look at an area that light is illuminating then you are probably best working with Illuminance which is measured in lux. The inverse square law looks how the area reflecting the light increases as you get further away, but if you can calculate the area reflecting the light from a known angle, distance and luminous flux (lumens).

With regards to your second question it would appear there is a roughly square relationship between the amount of light and what the eye perceives so...

Perceived light ≈ √Actual light


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