Greener Lighting for Greener Stages

by Richard Cadena

The typical 100-watt household incandescent lamp uses about a dollar’s worth of electricity to produce less than a nickel’s worth of light. The rest, about 97.4%, is radiated as infrared or pure heat, completely invisible to the human eye. Its overall luminous efficacy – the visible light output compared to the amount of power it takes – is about 17.5 lumens per watt compared to about 45 to 60 lumens per watt for a compact fluorescent lamp and slightly less for a typical LED profile luminaire. 

Coal Byproducts
About half of the world’s power plants are coal-fired, and they are the single largest source of carbon dioxide emissions on the planet. Some scientists believe that CO2 emission is the primary cause of global warming. Burning coal also releases other pollutants into the air. In addition to CO2, coal combustion byproducts include sulfur and many heavy metals like arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, radium, selenium, vanadium, and zinc. The sulfur reacts with oxygen and water to produce sulfuric acid, which falls back to earth as acid rain, and the mercury released into the atmosphere is the single largest unregulated source of mercury. 

To power a 100-watt incandescent lamp from a coal-fired power plant an average of three hours per night every day for a year, which is approximately 1000 hours, it takes about 110 pounds of coal and produces about 200 pounds of CO2. If, instead, we replaced that 100-watt lamp with a 24-watt equivalent with a luminous efficacy of 50 lumens per watt, it would take about 26 pounds of coal to operate and it would produce about 48 pounds of CO2, a savings of about 84 pounds of coal and 152 pounds of CO2. 

But wait, there’s more…
In a closed system like a building or a room, all of the heat generated by a lamp has to be removed by the air conditioning system if the temperature is to remain the same. Doing so requires the use of even more electricity. 

For example, a 100-watt lamp gives off 341 British thermal units (BTUs) for each hour of use, which increases the heat load by the same. The impact of that heat and the amount of air conditioning needed to remove it depends on the efficiency of the air conditioner. An air conditioner with a seasonal energy efficiency ratio (SEER) of 7.5 will use 34.1 watt-hours of energy to remove that heat. In effect, it increases the energy consumption of this lamp by 34%, adding to the cost, CO2 emissions, and pollution.

Efficiency Pays
A church in Houston was originally built in the early 1970s and the lighting was upgraded in the mid-1980s. It had three stained glass windows that were backlit with 190 1000-watt cyc lights and there were 168 1000-watt PARs used for the house lights. By replacing cyc lights with 109 324-watt T5 fluourescent fixtures and the house lights with 575-watt ERS fixtures, the energy consumption was cut by 55%. In addition, the lower power consumption results in a lower air conditioning load, saving even more energy and money. With a conservative estimate of 20 hours per week of use, an electrical cost of $0.0986 per kilowatt-hour, and a SEER of 10, in a year’s time, the building owner will save about $28,600.

Before:

Total energy consumed: 392,080 kW-hours

Total thermal load: 1,286,377 BTUs

Annual cost of electricity for A/C: $13,191

Annual cost of electricity for lights: $38,659

After:

Total energy consumed: 175,848 kW-hours

Total thermal load: 576,942 BTUs

Annual cost of electricity for A/C: $7,275

Annual cost of electricity for lights: $21,320

Total Annual Savings: $28,595

Amount of coal saved annually: 119 tons

Amount of carbon dioxide saved annually: 218 tons

Coal-burning power plants also release arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, molybdenum, radium, selenium, vanadium, and zinc into the atmosphere. Saving energy not only saves money, it also makes good environmental sense.