Radiant heat panels are very efficient. They actually heat a very large part of the cage because they cover a large part of the TOP of the cage (they're mounted to the roof).

Quoted from Pro-Products:

Safest

Cannot catch on fire.
Pro HeatTM radiant panels pose no fire hazard to objects in your cage, nor will they cause plastic to become deformed or melted.
Unlike heat lamps and ceramic heat emitters, Pro HeatTM radiant panels are safe to the touch with no danger of burning and scarring your reptiles.
Panel distributes heat evenly over entire surface with no hot spots.
Operating Efficiency

Uses up to 80% less electricity than other heating systems, costing only pennies a day to operate.
Pro HeatTM is the only heat source your reptile's habitat will require.
Eliminates the need and expense to continually replace heat lamps or ceramic heat emitters.

Best Heat Source

Replicates the sun's direct radiant warmth from above that reptiles require for proper thermo-regulation.
Automatically creates the proper temperature gradient within the reptile enclosure.
In addition to providing the right type of heat, Pro HeatTM radiant panels also provide added physiological benefits by lowering stress and improving your reptile's circulation, digestion, immune system and overall health.

Longest Lasting

Tests performed by the University of Maryland showed that these heaters will last up to 35 years and beyond.