I put a timer on one fluorescent light and started thinking about what I had talked about in one of my earlier watsonseblogs. This topic is very important, but is seldom considered, and lack of understanding and consideration causes a lot of waste and money. First I’ll have to discuss the way it used to be before CFLs replaced incandescent lamps.
Back when timers were used on 60 to 100 watt incandescent bulbs, the power that the timer used was a small fraction of the light bulb power. But the CFLs use 1/5 as much power as the old, inefficient incandescents, and the power that the timer uses is now a much greater percentage of the CFL power.
I will use the term Wh for the amount of Watt-hours that a device uses. If a 100 watt bulb is lit for 10 hours, it will dissipate 1000 Wh, or 1 kWh, which is 1 kilowatt-hour. This topic applies to the electrical control of any device, not just lighting.
One has to remember that the timer is on 24 / 7 and uses this small amount of Wh all the time. A mechanical timer may use 2 or 3 watts (you can feel it’s warm). If you are going to use this timer to control a small wattage lamp, then the timer may use, on the average, as much or more power as the lamp over time. If not more, then it may use a sizable fraction of the lamp’s Wh. This also applies to the motion sensors and daylight sensors that are often used in lighting fixtures.
What this means is that the timer is actually adding to your electric bill, not saving money. You will be better off if you remove the timer and plug the low power light in and control it manually. Let’s try an example. We have a 3 watt light controlled by a timer that uses 3 watts. We want the light to be on 6 hours a day and off for 18 hours. We want to save 18 times 3 or 54 Wh (watt- hours) a day. The timer uses 3 watts times 24 hours or 72 Wh. So in actuality we lose 18 Wh per day. We would be better off leaving the light plugged in 24/7 instead.
This same situation occurs when a light is controlled by a daylight sensor. I bought a nightlight that has a single LED and a daylight sensor. The sensor uses a 555 timer chip, which most likely takes as much or more power as the LED. It is wasting half its power or more during a 24 hour period.
Let’s think about the CFL. A common CFL lamp uses 13 to 20 watts, about equal to a 60 to 100 watt incandescent. The timer uses 3 watts. The timer is set to turn on the CFL for 6 hours a day. That is 13 watts times 6 hours or 78 Wh per day. The savings is 13 watts times 18 hours or 234 Wh. The timer uses 3 watts times 24 hours or 72 Wh per day. Subtract 72 from savings of 234 and it ends up actually saving 162 Wh a day. But if the CFL was being manually controlled, the savings might be equal to or better than 162 Wh.
One other factor we have to consider is the cost of the equipment – for instance a timer might cost $20.00 (US). If I add up the electricity savings of the timer over a year, it may add up to only a dollar or two. It may take ten or more years of savings to pay back the cost of the timer. And in my experience, the timers have a motor that stops working after a few years, maybe five or so years. Then it has to be replaced. in other words, the cost of the timer is never paid back in electricity savings. This hidden cost is very important, and should be brought to the attention of the consumer by the consumer agencies.
To sum it up – What we have here are a bunch of hidden costs that are literally defeating our attempts to save money and help the environment.
Update Sep 13 – I’ve been thinking about this problem. I received a LED light from my co-worker; he purchased it from Microcenter for 13 dollars. The brand name is Inland, it’s a 60 watt replacement, uses 10 watts, and is warm white. He wants to use them in a motion sensing security light. I figured that if the motion sensor circuit uses 1 watt and is on 24 hours a day, 7 days a week, the total use per year would be 8760 watt-hours or 8.76 kWh per year. If the light goes on at night for a total of 1/2 hour, the total use per year would be 1825 watt-hours or 1.825 kWh per year. Added to the motion sensor usage, that would total 10585 watt-hours or 10.585 kWh per year. The motion sensor clearly uses most of the energy in this case. Oops, I forgot; there are two light sockets. In that case assume only one socket is used, but even with two lights the motion sensor circuit is still the energy hog.
If he were to connect the single light directly up to the AC with no switch, it would run 24/7 and use 87600 watt-hours or 87.6 kWh per year. If it had a daylight sensor, assuming 12 hours a day average, that would be half as much or 43800 watt-hours or 43.8 kWh a year.
