Repti glow can get fairly hot, more wattage more heat. As for red incandescent bulbs, some nocturnal geckos are very sensitive to color even at low light levels, something in the range of 350x our sensitivity. However i can not say that this is the case for crested geckos, because the study did not involve them. But i assume its fair to say that they do probably see colors including red, which may make sense being that they are fruit eaters. however, this red light i double will disturb his day and night cycle. If it does concern you, a low wattage Ceramic (on a thermostat) would be the solution.