They will last 1 month to 12 months. The lifespan will depend on manner factors. The amount of time the heat lamp is used each day will impact its lifespan. Bulbs that are used continuously or for long periods will typically wear out faster than those used intermittently. The conditions in the reptile enclosure can also affect the lifespan of the bulb. If the enclosure is dusty or humid, it may reduce the lifespan of the bulb. Mishandling or improper installation can also decrease the lifespan of the bulb. For example, if the bulb is frequently switched on and off or if it's installed in a way that puts strain on the filament.
Using a reptile thermostat in particular, a dimming thermostat will increase the lifespan of your bulbs as it will regulate the heat and also turn it off gently which puts less pressure on the bulb. If you are not using a thermostat, you will generally need to replace your heat bulb monthly.
