Example of Relative Spectral Power Distribution

(REF: Wikiwand, Spectral power distribution)

Dir Amirhossein,

If the total emitted radiated power P is  known, one can find the scaling factor to get the absolute of the spectral power densities psd in units of joule/s per unit wavelength lambda.

By definition,

P= integral of p(lambda). dlambda over all possible wavelengths theoretically from mince infinity to plus infinity.

Alternative if the light source co version efficiency one can determine P by multiplying the input electrical power withdrawn by the lamp by the conversion efficiency.

Best wishes 

Thank you for your comments. Just to add a little comment to your previous comments, if the light source is an LED, the conversion efficiency is equal to External Quantum Efficiency (EQE). 

P(optical) = P(input_electrical)*EQE

P(input_electrical) = V(input)*I(input)

Also, usually by looking at datasheets of Xenon arc lamps, one can find an "average irradiant power", which I believe can be used as the scaling factor.