EGEE 102
Energy Conservation for Environmental Protection

Efficacy of Light Bulbs


Efficacy is the ratio of light output from a lamp to the electric power it consumes, and is measured in lumens per watt (LPW).

Type of lightbulbs and their outputs. Refer to the text description.
Efficacy of Light Bulbs
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Below is a list of different types of light bulbs and the light output of each (measured in lumens per watt):

  • Incandescent: 8 - 22
  • Mercury: 22 - 58
  • Fluorescent: 30 - 38
  • Metal Halide: 74 - 132
  • High Pressure Sodium: 74 - 132
  • Low Pressure Sodium: 70 - 152
  • LED: 10-200

Conventional incandescent lamps in a single four-way traffic light consume roughly 85 kWh of electricity per day and cost about $1,600 per year to operate. LED lights use just 10 percent of the electricity that incandescent lamps use, so the opportunity for savings is enormous.