Hi kenny,
leopard geckos need belly heat for digestion and lights will stress them if they are used 24/7. Even so called nocturnal lights. Besides, they don't need UV and heat mats are much cheaper in the long run. You don't need to keep replacing them, you can control the heat gradient of the substrate better, and they save on electricity.
The only time you would need a light for heat would be if your ambient air temps are getting too low in the winter. Even then, If you put the humid hide box halfway over the heat mat, the air temps in there will be sufficient.
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Rick-Geckoland USA
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