I know what wattage to use for a specfic tank. You say that you have a 4' x 1' x 1.5', but the only thing I know of similar to that is a 75 gallon tank (4' x 1.5' x 2') and I would use a 100W or 150W bulb/heat emitter for that if you are NOT using a heat pad in the tank. If you are, then use a smaller wattage bulb. It is your preference if you want bulbs (red/black for night and blue/white/yellow for day) or CHE. The latter lasts for about 7 years and bulbs only last 1/2 a year.