How much energy you need to get for the amount of illumination you want depends on three things:
Efficient controls and making good use of daylight also reduce lighting energy needs.
Using daylight effectively reduces electric lighting needs during daylight hours. Daylight is the least expensive light source. Light-colored interiors and window trim and good window placement make the most of natural light.
A variety of new compact fluorescent lamps produce more light for a given amount of energy, compared to standard incandescent bulbs. The new lamps save energy and generally have a longer life. Install them in high-use fixtures.
Light fixtures help distribute light and control glare. Some designs work better than others. Efficient designs typically are more open and use highly reflective surfaces. Direct light to surfaces and tasks, not to the floor. Choose fixtures that are easy to clean and allow easy replacement of lamps. Use lamps that the fixtures are designed for.
Fluorescent lights are the practical choice for efficient general lighting. Fluorescents are much more efficient than incandescent lamps. Multiply lamp wattage of a fluorescent by four to get approximate wattage of an incandescent with similar light output. For example, a 26-watt compact fluorescent lamp has the same light output as a 100-watt incandescent. Use fluorescent lamps with electronic ballasts. They don't hum or flicker and are highly energy efficient.
Your main lighting task for both full and half bathrooms is to provide light around a mirror, usually located above a sink. In small rooms, mirror lighting is adequate for general lighting.
Here are tips for lighting around a mirror:
Spread light over a person's face, not the mirror surface. Place lights on the sides, not the top, of the mirror to avoid face shadows.