Is it cheaper to leave a light on in a room when you will return within fifteen minutes?

Yes and no, it depends on the light. Even though you will always save energy when turning off any type of light, it may not always be cheaper for your situation.

If you have incandescent bulbs then shut them off every time you leave. Even if you come back to turn the same light on again in ten seconds. The second you turn an incandescent bulb off, you start saving energy and money. The incandescent bulb may burn out sooner if this is done often, but the electric bill will add up to a higher amount when the bulb is left on compared to the cost to buy another incandescent light bulb.

If you have fluorescent fixtures, such as in an office, you need to find out what type of Ballast (transformer) is being used to start up the fluorescent lights. If the Ballast in the fixture has been in use from before 1992, it is probably a Magnetic Coil ballast. A Magnetic Coil Ballast with 40 or 75 watt T-12* size fluorescent lamps means: It was considered cheaper to leave the lights on when leaving a room that you will return to within fifteen minutes. The reason for this is based on these old ballasts and lamps having their expected life decreased significantly when turned on and off several times a day. Thus bringing on the expense of new bulbs and ballasts, that was higher at the time, than the old low electric bills for when you kept the lights on until you return within fifteen minutes. This can still apply today if you are a non-profit or any organization that does not have the funds to change old lighting fixtures or replace parts, plus the labor. It would be cheaper for you to leave these old fluorescent fixtures on when returning within a few minutes to avoid contributing to the earlier creation of these high maintenance costs. This step, however, will only offer short term help to postpone the cost of repairs and/or the capitol expense of changing all of your old fluorescent fixtures.

*The T-12 or T-8 size stands for the diameter of a fluorescent tube. T-8 being a smaller diameter of 8mm.

Another reason to leave these old fluorescent fixtures on when returning within a few minutes or better still, to replace them with a new safe energy efficient fixture, is due to the hazard and expense associated with the old Magnetic Coil Ballast.** These ballasts have PCBs inside and have since been illegal to manufacturer for many years. This PCB hazard is very dangerous when it leaks out of the old coil ballast. Turning these old fluorescent fixtures on and off several times a day or removing any combination of fluorescent lamps from the fixture without replacing the lamps, may contribute to PCBs leaking from the ballasts due to extra heat build up. The ballast continues to work even if the fluorescent lamps it operates are missing from the fixture, thus increasing the risk that the ballast will over heat. Extra heat can also be created when the ballast is turned on and off continuously. Extra heat can cause the metal housing of the ballast to expand and allow room for the PCBs to leak out.

**These old Magnetic Coil ballast work two fluorescent lamps each. A Fixture with four fluorescent lamps will have two coil ballast working. Each Coil ballast working two 40 watt fluorescent lamps, in or out of the fixture, consumes approximately 16 watts and a Coil ballast working two 75 watt eight foot fluorescent lamps, will use approximately 30 watts.

RULES TO REMEMBER:

1.) If you see any black tar like substance on the lens cover of your fixture and/or it appears to be oozing out of the fixture, do not touch it! This may very well be contaminated with PCBs. Contact a License Electrician to dispose of the fixture properly and legally.

2.) Removing fluorescent lamps (bulbs) from an old fixture and/or not replacing the lamps to save energy or for any other reason, is dangerous. The old Coil ballast continues to work with the consumption of electricity, thus not saving much at all on the electric bill and contributing to the potential hazard of PCBs leaking and/or fire.

3.) Try to raise funds so that these old fluorescent fixtures with the old Coil ballasts could be changed. The new energy efficient fixtures with the new electronic ballast have a replacement cost that is justified by the savings off of today's much higher electric rates. The electric bill savings will not only present a payback on the new fixture, it will also save additional money for you or your organization.

If you have the new T-8 size fluorescent lamps in a fluorescent fixture with electronic ballasts or the new compact fluorescent light bulbs that use an Electronic Ballast, then shut those lights off as soon as you leave the room. The Electronic Ballast adds to the the savings on the electric bill, making the savings greater than the cost associated with the expected life of these bulbs being made shorter due to switching the them on and off several times a day. In fact, the 10,000 hour life of a compact fluorescent bulb is based on that bulb being turned on and off three times a day. The T-8, 32 watt fluorescent lamp working with an electronic ballast in a fluorescent fixture, has been reported to only uses about 27 watts of electricity in total when operating due to the electronic ballast!

Now, when you shut the lights you not only save on the electric bill, you also save BTUs for your air conditioning. Approximately 3.4 BTUs are saved for every watt no longer in use and not giving off heat. There are 12,000 BTUs per ton, thus using more efficient lighting will make the indoor environment more comfortable and save even more on the electric bill when the air conditioning is calculated in. -ehw