I've been using radiant heat on a milksnake for about 6 months, and just more recently on other kings.
RHPs direct long wavelength heat down, like the sun. What happens is objects below, be it rocks, wood, snakes, your hand, etc, will absorb the heat, even if the air temp in the cage is cool. That is the interesting thing about it. This type of heat does not dry out the air, since the long wavelength passes right through the air w/o warming it to any significant degree.
RHPs do emit residual heat, but it is surprisingly low. Far lower than any light bulb. Putting a thermometer in the cage does not always tell you much, since the snake can be 85 deg for example after it has been under the RHP for 30 minutes but the air temp shows 70 deg.
This is a different way to heat enclosures. We all know ground dwelling snakes make good use of undertank heating. Undercage heating or substrate heating is still very viable and effective. I'm here to say RHP heating works very well too w/o drying the substrate out so quickly. It also offers the snakes the ability to maintain a very wide body temperature range. I'm seeing these snakes use all temperatures, from the coolest to right under the RHP where, if sitting long enough, the part that is under the heat is 80-85 deg when shot with a temp gun. What their internal temp is like would be great to know, but I don't even try.
I use a dimmer plugged into an ON/OFF controller (Ranco for example). I set the ON/OFF setpoint around 80. When the inside air temp hits 80, I know the room is warm and will not cool down soon, so I prefer to have all heaters turn off. Under more "normal" conditions, the RHP is dimmed down about 1/2 power and the air temp in the cages is below 75. The snakes can be found hiding in any area of the cage for different reasons.
Back when I used racks, the snakes would coil over the heat almost all the time. With the RHP setup, the snakes warm up for awhile, then move away, then come back later, then move away again. During a shed they are right below the RHP.
Just look in the classifieds for radiant heat panels here on kingsnake. My cages come from different mfgrs. I have PVC cages and styrene cages. Any cage will work with an RHP. Wood, plastic, glass, doesn't matter. Cage in the pic is from Repti-Racks.
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Mark