Ceramic heat emitters are only recommended for use at night if your chameleons cage temp drops below 55*F. If temps remain above that, you wont have any issues .
A heat light is important because chameleons, like most reptiles, warm their bodies by basking under the suns light. Without the light they might not find a spot to absorb the heat they need.
As mentioned above, a regular incandescent house bulb works really well. I use a 75w for my enclosure.