Bright Lights, Bright Future Bob-O Schultze c.1992 Bob-O Schultze When Hornbrook Elementary School decided to upgrade the classroom lighting as a cost-cutting measure, they saved more than just money. By increasing the quality of lighting at the same time, they contributed toward the general well-being of the classroom environment as well. The Situation The main building, cafeteria, and classrooms of Hornbrook Elementary were built in the 1950s. Several extra classrooms and the gym were added in the early 1980s. While the newer classrooms were fitted with 4 foot tube fluorescent light fixtures using standard coil-core ballasts, the main building was fitted with incandescent lighting throughout. Each of the three classrooms used nine single bulb fixtures, each sporting a 300 Watt mogul-base bulb. These behemoths measure 9 inches long and are over 4 inches in diameter. With all nine lights on, as they are during school hours, the lights consumed a total of 2.7 kiloWatts. Figuring the classrooms were in use for eight hours a day and five days a week, that's 324 kiloWatt-hours per week for the three rooms. The school office used five of the same 300 Watt bulbs and fixtures which consumed 60 kW-hr per week. Other identified energy guzzling areas were the hallway with ten 100 Watt incandescent bulbs in various fixtures and five exit signs using two 40 Watt bulbs each. The hallway lights consumed 40 kW-hr a week and the exit signs consumed 16 kW-hr a week. Lighting Criteria Designing adequate lighting for the classroom or a workspace must take into account the quality as well as the quantity of light. Artificial lighting affects different people in different ways. Primary factors are the age and the seeing ability of the viewer, the glare, the length of time spent doing a given task, and the quantity (luminance) of light. As a rule, none of the primary factors except luminance can be controlled. As a result, more light and more power is usually used to compensate for the other conditions, rather than better quality of light or better fixture placement. While this approach works to one degree or another, it nearly always results in higher energy costs and an increase in the discomfort caused by glare. At the Hornbrook school, luminance ran from 84 foot-candles at desk level in the classrooms to 5 foot-candles in the hallway. A foot-candle is the amount of light that falls on a square foot surface one foot away from a lit candle. The number of foot-candles needed in a room depends primarily on the task being performed. Color Rendering Color rendering, an important measure of the quality of light, is measured on a scale of 0-100. A color rendering index (CRI) of 100 is supposedly equal to the color of sunlight at noon on a clear day. People and objects viewed under lights with a high CRI appear to be more natural. High CRI also gives the impression of a higher perceived level of light. This adds to its cost effectiveness and energy effectiveness. Color Temperature Color temperature is kind of misleading. It has nothing to do with the actual temperature of the lamp, but is a measure of the color appearance of light. It has a startling effect on an person's perception of his/her surroundings. Different color temperature is used to establish an atmosphere or change a mood. Color temperature is measured in degrees Kelvin and is described as warm, neutral, cool, or daylight. The color temperature chosen depends on the application. For example, a intimate restaurant might chose a color in the warm range (2300-3400øK) to set an intimate and personal mood, whereas an office area or a classroom would benefit from a cool range (3800-4500øK) which projects an appearance of neatness and efficiency. Other Considerations A certain percentage of people are also affected by the flicker or pulsing of 60 Hz alternating current, especially from fluorescent lighting using standard coil-core ballasts. Using electronically-ballasted fluorescent lamps eliminates much of this type of problem. Relamping the School The nine single bulb fixtures in each classroom were removed and replaced with 13 electronically ballasted, 4 foot 2-tube fluorescent fixtures. This decreased the energy use by 65%. Because of the much higher switching rate of the electronic ballasts, 20-30 kHz, all flicker should be eliminated. The lamps have a CRI of 80 and a color temperature of 4100øK. These lamps were chosen to emphasize the clean and neat classroom atmosphere. The light level jumped from 84 to 104 foot- candles and seemed to be better diffused throughout the room. The lights in the hallway and exit signs were replaced by 11 and 15 Watt compact fluorescent lamps with built-in ballasts. To minimize the initial investment costs, these lamps were retrofitted into the existing fixtures. Even though the energy usage dropped by 85%, the light levels didn't change, and the cooler color rendition gave the appearance of more light. The school office offered a good opportunity to combine naturally available light with efficient supplemental lighting. It also demonstrated a classic example of overlamping. The office has three large windows which more than adequately illuminate most of the workspace on a clear day. This area used the five 300 Watt bulbs to supplement the natural light during early morning, evening, and overcast days. The space is rarely used during the evening and there is some natural light available every day regardless of the weather. The school was able to retrofit four of the existing fixtures in the high ceiling with reflector-type 15 Watt compact fluorescent bulbs. The remaining incandescent fixtures were further from the natural light source and were replaced by two 4 foot 2-tube fluorescent fixtures. That's an energy savings of 86%. The Bottom Line The total cost for relamping the classrooms, office, exit signs, and hallway was $5462.87. Hornbrook Elementary will realize a savings of $88.72 per month just on electricity costs at the present rate. Since there is no chance of rates going down in the foreseeable future, this figure can only get better. Each of the 100 and 300 Watt incandescent bulbs replaced has a life span of approximately 1000 hours. They cost $1.00 and $11.00 respectively. The 4 foot fluorescent tubes have a average life span of 20,000 hours and the compact fluorescent bulbs are rated at 10,000 hours. The school should witness a savings of approximately $540.00 per year just in incandescent bulb replacement costs during the life span of the fluorescent lamps. This figure doesn't include labor costs for the maintenance person. Given a nine and a half month school year, the initial investment will be paid back in just under four years. Conclusion The graphs depicting the energy and dollars saved pretty much speak for themselves. In terms of dollars and cents, making the switch to energy- efficient lighting makes good sense, but that's just the beginning. Increasing the quality of light and life for our future generations has a value beyond money. It's priceless. Access Author: Bob-O Schultze, Electron Connection, POB 203, Hornbrook, CA 96044 ù 1-800-945-7587