Lux of a lightbulb

Question

The lux of a lightbulb is directly proportional to the wattage of the light bulb and inversely proportional to the area of the region the light is concentrated on. If a 60-watt light bulb emits 3600 lux per square meter, how much lux would an area of 8 square meters receive from a 120-watt light bulb?

Answer 1

Let L = lux, W = wattage, and A = area

 

Then, L = kW/A, for some constant, k

 

Since L = 3600 when W = 60 and A = 1, 3600 = k(60)/1

 

  So, k = 60

 

Therefore, L = 60W/A

 

So, when W = 120 and A = 8, L = 60(120)/8 = 900