Vivs can be heated in a variety of ways. The three most poopular are heat mats, light bulbs and ceramic bulbs.
A large viv may need more than just a heat mat to keep it warm, in which case you can use a light.
The light is there for heat and should be turned off at night (you can use the heatmat to keep the chill off during the night). Even red lights which snakes supposedly cannot see should really be turned off at night, as I believe snakes CAN see red light.
Alternatively you can use a ceramic bulb. These give out no light and lots of heat, and can be left on at night as they do not disturb snakes.
A light should be used with a dimmer stat, and a ceramic bulb should be used with a pulse stat. Personally I prefer ceramics for snakes as they do not need a light during the day providing the room receives some daylight or has artificial lighting.
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