Light Pollution Abatement Site Calgary Centre Royal Astronomical Society of Canada

Light and Greenhouse Gases

Energy Waste & Carbon Dioxide Emissions

Energy waste results from light pollution. Typically, 30 to 50% of the light we produce is never used, shining sideways or upwards instead. Misdirected light, using too much light, and leaving the lights on all night when nobody is around, are all wastes of energy.

Quality lighting can reduce electricity consumption and thereby reduce carbon dioxide emissions. In Alberta, most electricity is produced by at coal and gas fired generators. Each kilowatt-hour (one kilowatt-hour = one 100 W bulb left on for 10 hours) of electricity generated this way results in the emission of one kilogram of CO2 into our atmosphere. The use of energy efficient light sources should be encouraged. In the table below, the lights all produce about the same amount of light (lumens) but consume energy at different rates (watts):

Here's how to tell the difference between different outdoor lighting sources:

Incandescent: this common indoor light is very inefficient and has a relatively short life-span. Essentially, these lights are heat sources that also happen to emit some light. Much of the energy emitted is in the infrared. These lamps are okay if used in low wattage applications (e.g., Christmas lights) but are a poor choice for outdoor lighting.

Quartz: these are arc or filament lamps (like incandescent) and also produce glare. They are inefficient and have a short service life. These lamps are often used as spotlights or floodlights.

Mercury Vapour: this glary arc source that was the dominant source of outdoor lighting, especially street lighting, for many years. Much of the output was in the blue and violet ultraviolet (UV) portion of the spectrum, parts of the spectrum that the eye either does not see (UV) or does not focus well at night. The lamps' output fades with time and the lamps were typically housed in poorly shielded fixtures. It is usually cost effective to replace them with more efficient sources.

Metal Halide: these lamps are another common white light source. They are more efficient than mercury and being of more recent design, are usually housed in better fixtures that control light output distribution. If not well shielded, this arc source is glary. Look for them in parking lots and car dealerships where colour rendition is important.

High Pressure Sodium (HPS): these pinkish or amber coloured lamps are more energy efficient than any of the above sources. They are an arc source and can cause glare. Colour rendition is somewhat impaired because much of the emitted light is in the yellow through red part of the spectrum. Many communities, including The City of Calgary, have replaced mer-cury street lighting with HPS lighting. Unfortunately, usually only the lamps are replaced with HPS (at the same wattage) but not the old light fixtures (lots of light trespass, glare, and sky glow remains). Fitted into new, full cutoff light fixtures, these make good streetlights without the problems of light trespass, glare and sky glow.

Low Pressure Sodium (LPS): LPS lamps look yellow like the amber light in signal lights. LPS is a tube source, like fluorescent lamps, and are not glary under most conditions. Proper shielding can reduce glare further. Additionally, LPS lamps are so energy effi-cient (the most efficient avail-able) that a 55 watt LPS lamp has about the same output as a 100W HPS lamp or a 175W mercury lamp and three times the output of a 150W incan-descent lamp. This efficiency is due to all emitted light being in the visible spectrum, specifically the two sodium emission lines in the yellow-orange part of the spectrum and because the eye at night sees yellowish light most efficiently. Colour rendition by LPS is very poor, however.

In Alberta, a single 100-watt incandescent porch light left on all night shines 1/2 of its light into space and causes 390 kg of carbon-dioxide pollution each year. That's enough to fill 44,340 twenty cm (8") party balloons! From one light bulb!

Calgary will save over $2 million per year and reduce carbon-dioxide emissions by 18,000 tonnes per year after it converts to full cut-off streetlights and by using only as much light as necessary.

Approximately 25% of the electricity generated in the United States is used for lighting. In Canada, a similar percentage of electricity is also anticipated to be used for lighting. If energy efficient lighting were used just where economically sound, the electricity required for lighting would be reduced by 50%, with a national electricity demand reduction of 10%. Corporations will profit by lowering their electric bills, and reducing air pollution caused by electricity generation.