• Traditional incandescent lights are the most expensive for outdoor use.Jupiterimages/Photos.com/Getty Images
  
  Formerly ubiquitous incandescent light bulbs are slowing giving way to cheaper and more efficient compact fluorescent (CFL), high pressure sodium (HPS), and metal halide (MH) bulbs, as well as light emitting diodes (LED) for outdoor use. The annual cost of different kinds of bulbs depends on the cost of energy in a particular state or province. Watts measure amount of energy used; lumens measure the output of light. The fewer watts that a bulb consumes to produce lumens the lower the annual cost of using that bulb outdoors.
  
  

Compact Fluorescent Lights

• Natural Resources Canada says one CFL, a fluorescent bulb that lights mercury vapor, can use as much as 75 percent less energy while giving as much light as six to 10 incandescent light bulbs. A 25-watt CFL produces about 1750 lumens of light; a 100-watt incandescent yields about 1680. The consumer using a CFL for outdoor lighting pays for only a quarter of the amount of energy to get the same amount of light. Some models will not light in extreme cold temperatures. Sealed fixtures make the bulbs easier to start in the winter and allow the heat to escape during the summer. CFLs are good for lighting doorways and fixtures that are hard to reach.
  
  

High Pressure Sodium Lights

• High pressure sodium lights (HPS) initially cost more than other light sources. They use 40 percent less energy than fluorescent outdoor bulbs and 70 percent less than incandescent bulbs. They last about 10 years
  
  

Metal Halide Lights with PAR

• A 40- or 90-watt metal halide lamp, used in conjunction with PAR (parabolic aluminum reflector) is recommended as a replacement for 75- or 150-watt incandescent lights for outdoor security. Metal halogen lights last four times longer than incandescent bulbs and use 40 percent less energy. Their blue-white light is good to highlight plants in gardens. They generally use less energy than incandescent or fluorescent outdoor lights using similar PAR.
  
  

Light Emitting Diodes

• Light Emitting Diodes (LEDs) don't emit ultraviolet light so they don't attract insects. They are especially useful as lights above exterior doors and pathways when insects are a problem. Current LEDs yield 50 to 60 lumens per watt.
  
  

Incandescent Bulbs

• Incandescent bulbs incur the largest annual costs for outdoor usage. A 100-watt incandescent bulb will yield only 17 lumens of light. Most of the energy used by incandescent bulbs is turned into heat, not light.