Radiant Energy Absorption

Anyone fancy deriving the formula:

Q/t = (1000 W/m^2)eAcos(theta)

where (1000 W/m^2) is the amount of energy striking the surface of the earth at right angles per second per square metre, "e" is emissivity, "A" is the area of the entity and "theta" is the angle of incident light

-------- ignore the following if you don't care why i'm curious!

(I'm using it specifically to show a proportionality between energy absorbed [Q] and cos(theta) so that i can show that since

q=It

and

E=kq/r^2

so substituting (q=It)

E=k(It)/r^2

therefore

current is proportional to energy, indicating the fact that if a higher current is produced, more energy is involved.

then:

since energy is proportional to cos(theta), current is proportional to cos(theta).

this is used to discuss the efficacy of sunscreens in attentuating light incident upon a photovoltaic module (solar panel).

---------- just if you were interested as to why i want a derivation!)