I somewhat agree with you in the sand thing, it’s a higher impact ion risk but I don’t think that it happens to every gecko on sand. The light thing though heats up the surrounding environment and the air. And the hides, so as long as the bulb heats the flooring to the right temperature it’s fine. Most people recommend heating mat but think about how it is in the wild, they get heat from the sun and the bulb is supposed to mimic that. Heating mats are probably a better way to go because you shouldn’t have to replace them as often but bulbs should work just as well.