April 20, 2018

Lighting Audit

It is a relatively simple task to count the lighting fixtures (usually called luminaires) in a single classroom. However, it is sometimes harder to know what is behind the diffusing panel (usually called the lens). A typical Texas classroom will have about 9 luminaires with four bulbs inside.

There is more than one way to find out what kind of bulbs your classroom has. You could ask either the custodian (who changes them when they burn out) or the district energy manager. Or you could investigate inside one of the luminaires in your classroom.

The bulbs will have information identifying them printed on the glass at one end. For example, you may see F40T12CW printed on the bulbs. It sounds complicated but is really simple – it is just in a shorthand code.

F stands for fluorescent, 40 represents the wattage of the bulb, T stands for tubular, 12 represents the diameter of the tube (in eighths of an inch, or 1-1/ 2 inches in this case ) and CW designates the color temperature of the lamp (Cool White, in this case). This is the standard bulb found in classrooms today but it is yesterday’s technology and definitely on its way out. It is the least efficient choice available but may have a cheaper first cost than other options. New installations are very likely to have much higher efficiency components.

Your class can calculate the lighting use with several levels of efficiency:

Standard F40T12 with magnetic ballasts with no concern for use

Standard F40T12 with Watt Watchers (2 hrs/ day saved)

Upgrade to F32T8 with electronic ballasts

Each classroom is assumed to have nine 4-foot light fixtures with four fluorescent tubes each (or an equivalent). Such a fixture requires 192 watts of electricity (4 tubes at 40 watts each plus 20% for ballasts). The school year is assumed to last 180 days. Electricity is assumed to cost $0.08 (8 cents) per kilowatt hour (kWh). Two hours per day was chosen based on a teacher leaving the classroom at lunch for one hour and one other hour during the day (for example, preparation period, recess, the first hour after school).

If conditions differ at your school it is easy to recalculate your specific costs. The costs will still be huge at half this amount. If half of the teachers in the United States remembered to turn out the lights on their way to lunch (just one hour per day) it would save $34 million dollars every year. How many scholarships would that be? How many classrooms are in your district? Can your school district afford an extra $25 to $50 per classroom every year? Wouldn’t you rather spend the money on books or supplies for your class?

9 fixtures × 192 watts = 1728 watts × 2 hours × 180 days = 622,080 / 1000 watts = 622 kWh
(to convert to kilowatt hours)

622 kWh × $0.08 = $49.76

Standard F40T12 with magnetic ballasts use 192 watts per 4 foot 4 lamp fixture while producing 3050 lumens with a color rendering index of 73.

New F32T8 with electronic ballasts use as little as 101W per 4 foot 4 lamp fixture while producing the same 3050 lumens with a higher color rendering index (CRI-85).

Go through your school and do a lighting audit. When you are finished pass the report on to your administrators and explain to them the savings that can be incurred by doing a lighting retrofit project.