[CamperBob2]

Since the photon has nonzero energy E and is moving at c, it has mass by virtue of E=mc^2. And since E=hv, the E part is determined by the photon's frequency v, so the equivalent amount of mass is as well. It shows up as radiation pressure when the photon hits an object, just as if something tangible had collided with it.

On a sunny day, I'd guess that sunlight exerts about the same force on an acre on the Earth's surface as a postage stamp lying on the ground.

[red75prime]

E=mc^2 doesn't mean that a photon has mass. Photons do produce gravitational effects due to their energy, but not in the same way as a particle with mass m. See, for example, https://physics.stackexchange.com/a/6222

[CamperBob2]

A photon has no rest mass but it most certainly has mass-energy equivalence.

[mech422]

Thanks for the explanation :-)