The known Radiation Pressure equation is based on Special Relativity as I saw here: http://farside.ph.utexas.edu/teaching/em/lectures/node90.html I do not want relativistic. I want is a classical one that shows distinctivly the factor of brightness and the factor of frequency (colour) that increase Pressure. I.e. the ... brighter the light of the lamp is, the higher the Pressure. But brightness can change with no colour change. And also the higher the frequency, the higher the Pressure because that's what they say for gamma rays. I would not say no to a such equation that shows the "relativistic" E=hf because it is...not based on special relativity! They also say it for the phonon of the sound where there is no relativity there: Phonon is just a wavefront. I find it impossible to find that.