Topic: Crookes Radiometer affected by air pressure.

[Skywatch]

About 1.5 months ago, I took in a Crookes Radiometer. The little setup with the vanes one side Black one side White. Well after examining it, I noticed the radiometer was less sensitive to light at higher air pressures, while at lower pressures it is sensitive to even the dimist lighting conditions. Crookes Radiometers being set up like a light bulb, I understand the chamber is mostly vacuumed out, so this could have an effect by ambient air pressure. Is this true or is this just a theory?