The reasons are 1. No Light emitted Your pets will get used to large light emission from light bulb heater, especially when they need heat in cold winters. Some pets can hardly control themselves from being a long distance away from the light source. While such an adaption could eventually damaged their eye vision irreversibly. You would always need to keep light bulb on 24 hours a day. A non light heater will not disturb their day night conversion. 2. Resistance to humid areas amp terrariums Water proof design of ceramic heater allows them to work effectively in humid environments without burning out. This heater will not break even if water was tossed at it after 30 minutes of power on! So you do not need to worry if your pets may splash water onto it or be concerned of its weather tolerance. It will work in an open air garden