Pem’s Tech Blog

I Google’s this and ran into a Discovery Channel MythBusters video:
http://vodpod.com/watch/47235-mythbusters-lightbulb-experiment

I noticed that in this video that they used the Kill A Watt P3 device, which I also use.  They used the Kill A Watt P3 to measure average watts over 1 hour for each bulb in steady state: incandescent at 90 W, compact fluorescent at 10 W, halogen 70 W, metal halide 60 W, LED 1 W, fluorescent tube at 10 W.

Then they used a digital-based computer sampling oscilloscope, to measure the watts during turn-on.  There is a slight increase in watts as the filament warms up, but it’s not very long.  Their estimate/calculation said that you only save electric bill money by leaving the light on (versus turning it off when you leave the room), if the time (between when you turn it off then back on) is: incandescent at 0.36 sec, compact fluorescent at 0.015 sec, halogen at 0.51 sec, metal halide at ??? sec, LED at 1.28 sec, fluorescent tube at 23.3 sec.  (They skipped the number for the metal halide bulb).

Thank God, at the end of the video, they at least mentioned the other obvious cost question – how does startup affect the longevity of the bulbs?  They tested this by putting the light bulbs on a 2 minute timer, to have them turn on/off for 6 weeks.  At the end of the 6 weeks, every one of the light bulbs burned out, except the LED light bulb.  6 weeks * 30 times per hour * 24 hours/day * 7 days per week = 30,240 times.  Which they claim correlates to over 5 years of turning lights on/off in a regular household.  I wish they took it further, and compared it to a 15 min cycle, a 5 min cycle, a 30 second cycle, and a 1 sec cycle.

In summary, this very strongly argues that it’s generally better to turn off a light when you leave the room, at least in terms of energy savings.

However, it also argues that it’s not healthy to repeatedly turn the light on/off, in terms of longevity (lifetime of the bulb) (operating life of the light).  So this really left me wanting more data on how number of times turning a light on/off affects the operating life of the bulb.  Especially if we consider home automation, such as a motion sensor or a remote control or a light timer.

Finally, let’s not forget there may be some other factors.  For example, light use might in some way affect security / safety (like if having all your lights off increases chance of a burglary attempt), or eye health / comfort (if the light is too bright, and it hurts or damages your eyes), or distraction (from bright light).  For example, if you stare at a screen most of the day (like I do), then it might be healthier for your eyes to have background / ambient lights on and your monitor’s brightness down (warning: I didn’t research this in much detail yet).

I recall a story from the original “Home Alone” movie where the burglars decide to rob a house because they know the owners are on vacation because their light turns itself on via a timer at the same time every night.  Anyway, household security is important, but it’s not the focus of this current topic.

Pem (Admin) :: Oct.29.2009 :: Electricity :: No Comments »

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