Incandescent lights use a specialized resistor that slows down the electricity that flows through it. Some of the electrical energy is given off as light, but a lot is given off as heat, which is why these bulbs are not as efficient. The bulb must be air tight so the resistor filament does not burn out.
Incandescent light tends to be a warm white color, mostly because its light wavelengths pass beyond the visible spectrum and include many infrared wavelengths. This range, including red visible and invisible light, gives it a more natural color.
Standard incandescent light bulbs are great for everyday use in the home where “soft” light is desired. Some incandescent light bulbs are used not only for their light output but for their heat output as well. Heat lamps found in reptile tanks utilize the heat producing capabilities of incandescent bulbs to warm small, contained environments.
Never exceed the maximum wattage stated on your light fixture.