# Physics of an infrared thermometer

The thing about infrared thermometers that bugs me is how can you get the same temperature reading regardless of the distance to the object. Shouldn't there be a difference when measuring from two different standing points since energy flux density decreases with $${1\over distance^2}$$ and infrared thermometers work by focusing IR light on a thermopile, which then results in decreased (when measuring from further away) absorbed energy and therefore lower temperature and finally lower voltage across thermopile. Is there something I am getting wrong about this, or do IR thermometers make use of some other physics law like Wien's displacement law, by somehow measuring $$\lambda_{peak}$$ to determine the temperature?

I believe the basic answer is that, within limits, as you move away from an extended source, the IR sensor can collect flux from a greater amount of the surface. Your $$\frac{1}{distance^2}$$ formula only holds for a point source.