I am trying to understand the relationship between two measures of light: lux and candela. It is probably easy for those with longer experience, but here it goes:
I have learnt (here for instance) that lux equals candela per square meter. But this feels too "simplified" - doesn't the distance from the light source to the area have any impact? A thought experiment:
Imagine that we have a hollow cylinder (yellow in the figure above) with a length of L (say 1 meter) and a inner diameter of D, say 0.1 meter.
In the end of the cylinder there is a lux-meter, measuring the amount of light reaching the end of the cylinder (as measured in lux).
If we would place the tube in front of a light source with a light intensity of 1 candela, what would the lux-meter show?
If we set the inner diameter D to 0.1 meter, the end of the cylinder will have an area of ~0.0078 square meters. But is the lux then simply 1 candela divided with this area? Doesn't the distance from the light source to the area have any impact?