Light Bulbs

Least Green

Incandescent
Advantages
Inexpensive
Widely Available

Disadvantages
Inefficient, Most of the energy is turned to heat

More Green

Halogen
Advantages
Bright White light
Nearly efficient as compact fluorescent
Disadvantages
Very hot, posing a safety hazard
Needs a filter because they emit a lot of UV light.  Without the filter they can give you a sunburn.
Must handle with gloves or a paper towel because fingerprints will cause a hot spot to form leading to an explosion hazard.

High-Intensity Discharge
Advantages
Very Bright light

Disadvantages
Expensive
Operate very hot
must be used with a UV filter.
Can cause eye damage and severe sunburn

LED
Advantages
Very long life, usually more than 100,000 hours up to 1,000,000
Energy efficient, new breakthroughs in technology will make LEDs more efficient then Compact Fluorescent in a few years.

Disadvantages
Very Expensive

Greenest

Compact Fluorescent
Advantages
Widely Available
Most efficient bulb available today
Last much longer then Incandescent or halogen

Disadvantages
Emit UV light, enough to fade art or furniture over long periods.
More expensive than Incandescent.
Contain small amounts of mercury.  Must dispose of properly.

More Information
Philips