EGEE 102
Energy Conservation for Environmental Protection

Efficacy of Light Bulbs

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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.
The image is a horizontal bar graph comparing the approximate efficacy, measured in lumens per watt (lm/W), of various lighting technologies. The x-axis represents the efficacy scale ranging from 0 to 160 lm/W, while the y-axis lists different lighting types: Incandescent, Halogen, Compact Fluorescent (CFL), Linear Fluorescent, High-Intensity Discharge (HID) including High-Pressure Sodium (HPS) and Metal Halide, and LED.
Click for a text description of the image.

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
Credit: Slide #35 "Led Basics(link is external)." University of Coimbra. July 2017.

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.