This is going to confuse you, but lites have very little to do with monitors. Ok, nothing to do with monitors.
95% of wild monitor activity has nothing to do with the lite from the sun either. Their activity is based on heat and heat held(absorbed) from the sun.
This is the same with captives, They use heat, they do not care where it comes from. They have use for heat 24/7 not when ever you decide to turn the lite bulb on(which has nothing to do with monitors) When they have a need for heat, like a meal sitting in their stomach, they seek heat, 24/7, not just when the suns up. In fact, 90% of varanid activity is out of the lite of the sun or litebulbs. That is, if that have the heat to be active. If not, they will seek whatever gives them enough heat, whether its a litebulb, heatpad, the sun and more.
Also, do not be confused, a lite bulb is not the sun, you know its not(hopefully) and your monitor knows its not. Its only a heat source. A heat source no different then many other heat sources.
Try taking the lites out of the cage. and aim them on the side of the cage. Where it heats the side. The monitor will go there, then move it to where it heats below the surface, the monitor will make a burrow and go there. Or do both, one heating the ground and one basking spot. Your monitor will use both, for reasons of its own. If you leave both on 24/7, it will still use both, but not use them in a way that suits you, it will use them in a way that suits it. For instance, many(but not all) individual monitors will choose to bask at night because that avoids YOU. You scare them, so they will avoid you. Of course if you give them a reason to meet you, like at feeding time. They will arrange their schedule to be out at feeding time, then go down and wait until your not there and then come out and bask.
Many individual monitors will bask at night to avoid their own cagemates, not all of the time, just some of the time, when they have a need too. Some hang out with other monitors in the day, for short periods, and then bask by themselves when the other monitors are sleeping or in burrows. They do this because they have a need to.
Slowly to the point, to listen to your monitor, you have to give it choices to make, then you can listen. If you tell it what to do(lack of choices) it can only do what you tell(allow) it.
Think about this. Reptiles do not know or care what day or night means, or nocturnal or diurnal. Those things mean absolutely nothing to them. What is meaningful are the conditions they provide. The sun heats objects, they use these heated objects. Light is a dangerous companion to heat, it means, monitors predators can see them. They would perfer to not be seen. See, I told you I would confuse you. Cheers
