Is Beer-Lambert law also valid for fluorescence and luminescence? When I measure optical density in a microplate reader the absorbance is proportional to the concentration and the height of the liquid. Is Beer-Lambert law also valid for fluorescence and luminescence?

Let's say I prepare a fluorescent solution and measure e.g. the signal of 100 μL and of 50 μL. Do I get the half signal for 50 μL?
No the Beer Lambert law  ($I_{trans}=I_0\exp(-\epsilon[C]L)$) does not apply as this shows that the transmitted light intensity decreases exponentially with concentration as it passes through a solution. 

Fluorescence/luminescence is directly proportional to the concentration of molecules excited provided that the solution  is dilute so that dimers or excimers are not formed and that self-absorption of the fluorescence light by another part of the same solution does not occur.