A 75W bulb should be too much if anything, usually 25W should be sufficient. How and where are you taking your temperature readings? You should use a digital thermometer on a branch/basking spot closest to the bulb, so a few inches away from the light. Don't use analogue thermometers as these will measure the ambient air temperature and not the basking spot temp. Night bulbs can be used but will need to connected to a dimming thermostat so the night temperatures can be set lower than the day time temperatures, a night time drop is important for all animals. Fluorescent lamps and preferably a UVB will provide the day and night cycle.