Light Bulb Types Explained...

Metal Halide
Metal halide light bulbs produce a crisp white light giving good colour definition and a high light output for their size. Originally created for industrial use in the late 1960s, metal halide light bulbs are now available in numerous sizes and configurations for both commercial lighting and residential applications. This light is great when used in outside applications as visibility is very good due to the intense white light emitted.
Overall: a compact powerful and efficient light source that gives good colour definition suitable for most applications.

High Pressure Sodium
These light bulbs produce a dark pink glow when first started, and then proceed to an orange light once they begin to warm up. They are widely used for outdoor lighting such as street lights and security lighting, and other applications include building floodlighting and general area lighting.
Overall: an efficient light bulb used where an instant start is not required and where good colour definition is not so critical.

Mercury
These light bulbs are very similar to high pressure sodium when it comes to both price and light output, but they produce a dark almost grey output when first struck, and then produce a dull white light when warmed up. Applications include, industrial lighting, car park lighting and general floodlighting.
Overall: a fairly efficient light about a 3rd as efficient as metal halide and used for general lighting applications where really good colour definition is not critical.

Compact Fluorescent
In comparison to other light bulb types, compact fluorescent (CFLs) have a longer rated life and use less electricity. In fact CFLs save enough money in electricity costs within the first year to make up for their initial higher price. CFL bulbs give off a very good crisp white light.
Overall: a very efficient, cheap to run light bulb with a long life giving even white light distribution and excellent colour definition. Most suited to lighting smaller areas.

Wattage and Brightness
Named after James Watt, the inventor of the steam engine, the Watt is a standard international unit of measurement of power. In the case of electric lamps, the Wattage of the lamp defines the amount of electrical power that it consumes and is also related to the brightness of the light bulb. However, since different types of bulbs are more or less efficient in converting electrical power into light, the watt is not in itself an exact measure of brightness. For example, a 20w Compact fluorescent light bulb is approximately as bright as a 100w standard incandescent light bulb, yet it consumes only one fifth of the electricity.