The bulb does not necessarily have to get hot to warm water (although it can't hurt) ... just the light (which is energy) is absorbed by water increasing the temperature .. albiet should not be by much. See if this scenario applies .... You have a large (surface area) heated, constantly lit tank in an air conditioned (low humidity) room where air is flowing (from a fan or vent) over the tank.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.