The bulb’s intensity depends directly on the size of the tank; a bigger tank will require more light compared to the smaller one. You can use Repti-Sun 5.0 for a 20-gallon tank; whereas, the 40 gallons tank requires a Repti-sun 10.0 bulb. Repti-sun 5.0 is not suitable for bigger tanks and adult bearded dragons, as they require a bigger living space, where this light won’t work.