In article , Jeff Liebermann writes:
Photon (RF or light) pressure have been measured in the laboratory by
using two pressure gauges, blocking RF and light from one gauge, and
measuring the differential pressure. The differential measurement
cancels external influences, such as gravity, wind, earth movement,
etc.

Maxwell's equations - classical field theory - predict light
pressure even without photons and quantum theory. Double slit
experiments show interference patterns are followed even by
single photons allowed to to pass - exactly as if each photon
converted to a wave and portions passed through each slit and
thus _the photon interfered with itself_.

You really have to observe quantum effects before you can
register individual photons.

And, with e = h nu, nu being frequency, quantum effects at UHF
and below are much harder to see because each photon has such
low energy.

George