You don't need a heat lamp. The ambient temps in your home along with a low wattage bulb is usually good enough. You can partially cover the top with glass over a screen top.

I have an Exo-Terra with a screen top and I partially cover 70 percent of the top with glass. Humidity is 85-95 and temps about 78 and the bulb I use generated almost no heat. My bulb is about 10 inches above the tanks top.