It really depends on the overall heating arrangement in your bearded dragon tank.
If your heat bulb is only providing a hot spot for basking and there are under tank heat mats, ceramic heaters, hot rocks or similar providing a general warm background temperature then, yes, it probably can be switched off over night. In fact there is a good deal of evidence to suggest that a night-time temperature drop can be very beneficial with a whole range of reptiles – especially if you’re hoping to breed. The idea behind it is pretty obvious really – come sun down, even in the tropics the temperature drops – so mimicking this in the terrarium allows animals to experience as natural a day/night cycle as possible. How much you allow the temperature to drop obviously depends on the animals concerned – desert temperatures plummet once the night falls, but for bearded dragons, around 5 degrees C should be about right.
However, if it is the only source of heat in the tank, then switching it off is more problematic and you might want to think about changing your set up to allow you to maintain the ambient temperature by other means, and only run your heat bulb during the “day”.
Heating and lighting in the terrarium are two of the most critical elements in your pet’s environment and controlling them properly is a major factor in ensuring that your lizards do well. It’s worth investing in the highest quality of thermostat you can afford to control the heating system in your tank – dimmer-stats being one of the best kinds, especially if you’re using a spot lamp. These sophisticated bits of kit gradually reduce the electricity once the right temperature has been achieved, which avoids the “lights-on, lights-off” effect that happens with the older types of thermostats. It’s also gentler on the bulb’s element – which tends to make it last longer.
However, to achieve the best control over the environment in your bearded dragon tank, there’s nothing to beat the latest generation of thermostats, which will automatically maintain two different temperatures – one for daytime and one for night – which really makes conditions in the terrarium about as near-natural as you can get.
Just add a timer to your lighting arrangement – if you haven’t already got one – to control the length of the day and night, and your dragons will be well away!