One of our main uses for electricity is for lighting and the choice of lighting is very important in a solar powered system.

Low Voltage Lighting

This will obviously be the choice for those with a small system without an inverter to produce "mains" voltage AC power. The modern bulbs used will be more efficient than the "traditional" incandescent mains voltage bulbs not as efficient as "low energy" bulbs.

Incandescent Mains Voltage bulbs

These are the filament bulbs invented by Thomas Eddison (or at least he developed the first commercially viable bulbs) which are ingeneral use today. They are however not as efficient as alternatives and do not there for have a place in a solar powered system.
These bulbs produce light by using electiricity to heat the filament (in an inert atmosphere) to a high enough temperature to glow and emit light. However, only about one third of the energy is emitted as light, the rest is heat.

Low Energy Light Bulbs

These are actually miniature flourescent bulbs which use approximately one quarter of the energy of an incandescent bulb and should also have a much longer life.
These bulbs are available in a choice of light output (slightly different colours) though this information is not always available on the box. The colour is quoted as a colour temperature (no connection with the actual temperature of the bulb) quoted in degrees Kelvin (°K)
An attempt to illustrate these colours is shown below.

2700oK

3500oK

500oK

The colour temperature relates to the property of matierials to give off light when they are hot.
Steel glows red when it is at around 600^oC (873^oK). As it is heated to higher temperatures, the light given off becomes more white and eventually has a blue tint.
A degree Kelvin is the same as a degree Celcius but 0^oK is at -273^oC