What night actually needs to look like
Crested geckos are night-active New Caledonian geckos built for mild forest evenings, not tropical heat. They do their feeding, exploring and socialising in the low-to-mid seventies Fahrenheit, and a natural night drop of a few degrees is part of their rhythm — keepers in warm homes worry about cresties overheating far more often than chilling. The comfort floor sits around the mid-sixties: sustained nights below that slow digestion, blunt appetite and leave a gecko lethargic at the hours it should be hunting. So in a cool bedroom the question is precise — how cold does the enclosure's overnight minimum actually get — and it has a measurable answer.
Measure the real low before buying heat
Bedrooms lie about their temperature: the thermostat sits in a hallway, the window wall runs cold, and the coldest hour lands just before dawn. Put a digital thermometer with a minimum-reading memory inside the enclosure at perch height, leave it for three typical nights, and read the recorded lows. A tank on an exterior wall, in a window draught, or on a cold floor can run several degrees below the room's daytime feel. Often the fix is placement, not equipment: move the enclosure to an interior wall, raise it off the floor on its stand, and close the gap between tank and window. Re-measure after moving — many 'cold' crestie tanks were simply standing in the room's one cold river of air.
Gentle heat, controlled, if you truly need it
If the lows still sit under the mid-sixties, add heat sized to lift a few degrees, not to create a basking spot. A low-wattage ceramic heat emitter above one end, or a heat mat fixed to the outside of one side wall, both work — each on a thermostat with its probe inside at perch height, set to hold the night minimum and no more. Never use a bright night bulb: this is a nocturnal animal whose active hours should stay dark, and light at night disrupts the very behaviour you are warming the tank to support. Warm one end only, so the gecko can shuttle between the lifted zone and the cooler side as it chooses. Once a week, press the back of your hand against the warm-side glass and the perch beneath the emitter: thermostats and probes fail quietly, and a mat or emitter running unchecked can push a small tank far past comfort before the nightly check would notice.
Watching the gecko through the cold months
Your gecko grades the setup nightly. A crestie that emerges at dusk, fires up, eats its prepared food and licks droplets from the leaves is telling you the temperature is right, whatever the gauge argues. One that stays curled in the same foliage for nights on end, ignores food it normally takes, and feels cool and sluggish to a warm hand is living too cold — re-check the probe position and the thermostat before assuming the heater is too weak. Misting in the evening raises humidity for the active hours and pairs naturally with the nightly check. Keep those winter readings somewhere durable: in KinsLe, Care Teams carries the evening check — temperature low, misting, food offered — so a cool spell never goes unnoticed for a week.