by Pajarita » Sat Jul 04, 2015 9:38 am
If I remember correctly (light is a super difficult subject and I barely grasp the basics, mind you) it IS the curvature of the earth and the way the sun light 'hits' the atmosphere that makes it refract differently than when it's straight down but this ends up in less UV and more IR.
As to the question, you can use any kind of light as long as it doesn't shine at all on the bird (especially at night) but in order for this to happen, you need to use some type of black out material between the light source and the bird itself which, when it comes to heat lamps, you can't because putting a material near a source of heat will end up creating a fire or smoldering. Aside from this, heat coming from a single focus (as in a lamp which you need to put outside the cage and, usually, at mid height) doesn't diffuse as evenly as when it comes from a surface (as in a panel or pad, in this case), so you end up with a central spot that is super hot and radiating from this center the heat diffuses more and more until it's nothing left so the corners of the cage would be cold - while with a pad under the cage, you are heating up the entire cage (as long as you cover the sides and top to 'hold' it in)