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Want to save the planet - best to have movement sensor lights, low watt bulbs or both

Want to save the planet - best to have movement sensor lights, low watt bulbs or both


Old 01-01-07, 10:28 PM
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Join Date: Dec 2006
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Want to save the planet - best to have movement sensor lights, low watt bulbs or both


I have just replaced every bulb in my house with low energy sticks / bulbs.

OK, they take a while to achieve full brightness, but once they have it gives my halo (and my wallet) a glow knowing that they are all burning less than 1/4 of the electric the previous bulbs were.

Again, saving the planet, my wallet and reducing the light pollution to the sky I have put sensor lights in my porch so that they are only on when needed.

I heard a long time ago that the usage of electricity to turn on a fluresent tube was quite high but once on continuing the light required only a trickle of energy. Meaning that in some cases it uses less energy leaving the light on rather then wasting electric keep turning it on and off.

With my sensor lights am I actually burning up more electric with them on-off-on-off than simply leaving them on all night ?

They are 18W bulbs (equivalent to 100W filament bulbs). Is there an equation to work out how much energy is used turning them on and how much the trickle is. Then how much an 'on off' is worth compared to a 'stay on'.

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Old 01-02-07, 06:09 AM
Join Date: Sep 2002
Location: welland ontario
Posts: 5,676
The more energy to turn on bulb statement is false. Turn them off when ever you don't need them.
Old 01-02-07, 10:00 AM
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
There is actually a nugget of truth on the energy usage issue.

(Well, two nuggets of truth.)

For both incandescent and fluorescent lighting, there is some extra power used when starting the lamp. In the case of incandescent lighting this 'inrush' can be as much as 10x the normal power demand. This inrush is significant enough that things such as control relays often have different ratings for incandescent lighting versus 'normal' loads. However the duration of this inrush is so short that it makes no difference in terms of measurable power consumption. Given the choice between turning a lamp off for 1 second versus leaving it on, you use less energy if you turn the lamp off. This is true for fluorescent lighting as well.

The second issue is lamp life.

For many types of lighting, including fluorescent, turning the light on uses up a small chunk of the overall life of the bulb. The bulb might be good for 20000 hours if turned on once per day for 4 hours, but have a much shorter life if turned on 10x per day for 15 minutes per time. The specifics are different for each type of lighting, so you would need to hunt down details for your bulbs in particular.

Since it costs money and energy to make a bulb, decreasing its life can be considered 'using energy', and it certainly costs money.

You will want to adjust your sensor to leave such lights on for a 'reasonable' time, so that they don't flick on and off several times during periods of high use.

But in general, it is better to have the light off. My hunch is that the energy used in 5-15 minutes of use is greater than the energy cost of the bulb light lost by turning the bulb off and then on again.

Old 01-02-07, 10:57 AM
Join Date: Sep 2003
Location: Central New York State
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One further comment. I believe that years ago it used to be true that fluorescent lights used a lot of energy to start. I am talking about 30 years ago. I was always told in grade school that the amount of time was about 20 minutes. If you were going to be away for less than 20 minutes, it would cost less to leave the lights on.
Old 01-02-07, 11:14 AM
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This has been mythbusted as well.

MythBusters measured the power useage of all different bulbs, florecent, incadecent, LED, etc.

The florecents used the most energy out of them all, but, they said the amount of power usage used during turning unit on is equal to 20 seconds of continual usage.

They said to shut any type of light off when not using it.
Old 01-02-07, 11:16 AM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Mythbusters was not around 30 years ago, and the lights have changed an awful lot since then.

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