[Netheron]

The photons have a momentum, not a mass.

Anyway, the windmill/lightbulb doesn't really have much to do with photon momentum, it has more to do with differences in temperature on the vanes and the gas molecules inside the bulb.

[The_Victor]

The photons have a momentum, not a mass.

But in order to have momentum, mass is required. Photons have no rest mass, but since they are never at rest, they have a measurable mass, even if that mass is purely associated with it's velocity.

[The_Victor]

differences in temperature on the vanes and the gas molecules inside the bulb.

The bulb is supposed to be pumped down to a vacuum.