EPA of Lighting Fixture

[Illuminator]

I am being asked to specify the EPA (effective projected area) of one of our lighting fixtures. How is this calculated?
Is it:
a) Merely the cross sectional area of the fixture normal to the wind direction.
b) The cross sectional area times a coefficient that accounts for the shape of the fixture.

Does wind speed and altitude above the ground come into consideration when supplying a EPA figure?

Thanks in advance,
Gabriel