This calculator allows calculation of irradiance (W/m^2) from radiant flux or radiation intensity (W,W/sr) and conical apex angle (°).
LEDs are often described as having some radiation intensity and a viewing angle. This calculator will give the radiant flux.
The calculator assumes uniform flux distribution though the apex angle, but in reality flux will vary. Using a lower 'average' luminous intensity is one method of adjusting for non-uniform distribution.
If power is provided, it also calculates luminous efficiency.
If radius is given, it also calculates irradiance.
The results can serve as a saneness test on published product claims.
The calculator does not do a lot of error checking, if you enter nonsense, it will probably produce nonsense.