When is it more frugal to leave lights on?
Jennifer Fresco
I remember reading that since lights use x amount of energy
per minute, and it takes more than that to start up a light bulb,
it is more frugal to leave the lights on for short periods of time
than to turn them out when leaving a room you are going back to soon.
I remember also that it is a longer time for fluorescent lights, as they
take more energy to start, and use less energy as they burn.
Is anyone able to quote real amounts of time for this rule?
Jennifer
Don Klipstein
Jennifer Fresco (jennifer....@sci.fi) wrote:
: I remember reading that since lights use x amount of energy
Although an incandescent bulb consumes eye-popping amounts of power when
first turned on, it does so for less than a tenth of a second. Turning it
on uses less extra power than running it for one second does.
Fluorescent lamps have little to no increase in power consumption when
started. At least not for more than a couple hundredths of a second.
A more important consideration is lifetime.
Incandescent bulbs usually burn out when they are turned on. However,
in most incandescent and halogen bulbs, turning on the bulb does not cause
fatigue to the filament even if you can hear the filament expand.
(There are some exceptions - a few bulbs may well fatigue from cold
starts.) Burnout during turn-on results from a temperature overshoot of
thin spots in the filament. A filament that has aged enough to be unable
to survive a cold start is usually through 98-99 percent of its life
anyway.
Although soft-starting devices are widely rumored to greatly extend the
life of light bulbs, they do so mostly by dimming the bulb slightly.
Some halogen bulbs may last incredibly long with both soft starting and
a small amount of dimming. Non-halogen bulbs will usually last longer by
leaps and bounds when dimmed, but this is usually unfrugal. Getting a
given amount of light from incandescent bulbs usually costs more with
dimmed or extra-long-life bulbs than with 750 and 1,000 hour bulbs.
Cooler running filaments are surprisingly less efficient at producing
visible light, and most of the cost of incandescent lighting is the cost
of the electricity to run the bulbs instead of the cost of buying bulbs.
More details in my incandescent and halogen lamp document, at:
http://www.misty.com/~don/bulb1.html
Fluorescent lamps actually get some life taken out of them by starting
them. How much? This varies. Most figures I see say that cheaper 4-foot
tubes cost less to leave on only if they are turned off for less than 5
minutes, since the bulbs are cheap. Lower wattage ones and compact
fluorescent lamps should stay on instead of being turned off for 15-20
minutes. Compact fluorescent lamps 15 watts or less without detachable
ballasts should probably stay on instead of being turned off for up to
20-30 minutes. Instant start lamps have more wear per start than preheat
and rapid start lamps and lamps in trigger start fixtures - do not turn
off instant start lamps if they will be turned back on in 10 to 30
minutes, depending on wattage. Lower wattage fluorescent lamps are more
unfrugal to turn off and back on, since turning them off saves less
electricity while lower wattage bulbs are not proportionately less
expensive.
Costs of keeping a fluorescent lamp on vs. turning it off and back on
vary with your power rates. Where electricity costs the least, the
savings of turning the lamp off are the least.
Fluorescent lamps are not the most frugal lamp type where they are
turned on briefly and usually off, as in closets, refrigerators, and some
bathrooms. Use incandescent lamps in these places. Do not use halogen
lamps in refrigerators and closets, since the halogen capsule must warm
up for the halogen to clean off evaporated filament material and return it
to the filament.
Hope this explains some things!
- Don Klipstein (d...@misty.com)
http://www.misty.com/~don/index.html
http://www.misty.com/~don/light.html
http://www.misty.com/~don/f-lamp.html
http://www.misty.com/~don/cf.html
http://www.misty.com/~don/cfbest.html
nicks...@ece.vill.edu
Jennifer Fresco <jennifer....@sci.fi> wrote:
>I remember reading that since lights use x amount of energy
>per minute, and it takes more than that to start up a light bulb,
>it is more frugal to leave the lights on for short periods of time
>than to turn them out when leaving a room you are going back to soon.
It's always a good idea to turn off lights, from an energy point of view.
>I remember also that it is a longer time for fluorescent lights, as they
>take more energy to start, and use less energy as they burn.
A compact fluorescent loses about 6 minutes of lifetime (0.001% of its
10,000 hours) every time you turn it on, so you might leave it on for a
few seconds when leaving a room, to save 0.01 cents of a $10 bulb cost,
while consuming 10W/1,000/60x10 = 0.0016666... cents per minute's worth
of energy at 10 cents/kWh. Frugal people might turn it off if they were
going to be out of a room for more than 6 minutes, at which point the
energy saved is worth more than the increased bulb lifetime...
Nick
Dave Garland
JF> From: Jennifer Fresco <jennifer....@sci.fi>
JF> I remember reading that since lights use x amount of energy
JF> per minute, and it takes more than that to start up a light
JF> bulb, it is more frugal to leave the lights on for short
JF> periods of time than to turn them out when leaving a room
JF> you are going back to soon.
The increased electricity it takes to start a light is trivial. However,
the fact that turning a light off & on shortens the bulb life is real.
For incandescent bulbs (high power consumption, cheap bulbs) it is almost
always more frugal to turn the light off. For fluorescent lights (low
power consumption, high wear & tear at startup, expensive bulbs) the
"cheaper to leave it on" time will probably be significant, and more so
for compact fluorescents (bulbs are even more expensive).
I don't have any real numbers. Personally, I leave fluorescents on if
I'll want them on within the next hour or so. My porch lights (7W compact
fluorescents) stay on most all of the time, as the cost is minimal (a
couple of bucks a year) and in cold (below freezing) weather they have
trouble starting.
-Dave
dave.g...@wizinfo.com
Dave Garland
DK> From: d...@Misty.com (Don Klipstein)
DK> Fluorescent lamps are not the most frugal lamp type where
DK> they are turned on briefly and usually off, as in closets,
DK> refrigerators, and some bathrooms. Use incandescent lamps
DK> in these places.
This is true, but... fire codes are starting to frown on incandescents in
closets (especially if they are not in an enclosed fixture) due to the
proximity to flammable materials (clothing). An incandescent bulb is hot
enough to start a fire if it comes into contact with cloth.
-Dave
dave.g...@wizinfo.com
Dreamer
Don Klipstein wrote:
> Incandescent bulbs usually burn out when they are turned on. However,
> in most incandescent and halogen bulbs, turning on the bulb does not cause
> fatigue to the filament even if you can hear the filament expand.
> (There are some exceptions - a few bulbs may well fatigue from cold
> starts.) Burnout during turn-on results from a temperature overshoot of
> thin spots in the filament. A filament that has aged enough to be unable
> to survive a cold start is usually through 98-99 percent of its life
> anyway.
Maybe someone can answer a question for me. Why is it that some bulbs
burn out faster than others? I am thinking specifically of my ceiling
fan which has 3 lights in it. I am constantly replacing the same bulb,
the other two have only once needed replacing. I had thought that it
was the fixture or the wiring but... another light in our house burns
out unbelievably fast, and in that room we not only replaced the fixture
but had it rewired completely when we renovated and that room is now on
its own circuit. Yet it still burns out within a month. This to me
seems excessive. I have even tried buying more expensive bulbs to see
if the quality is different. Any explanations? Power surges? Aliens
sucking the light energy? <g>
Someone once told me they bought light bulbs with a lifetime or 20 year
guarantee or something, wish I could find some of those!!
ha...@chickpea.com
Dreamer <dre...@spamfreehotmail.com> wrote:
>Maybe someone can answer a question for me. Why is it that some bulbs
>burn out faster than others? I am thinking specifically of my ceiling
>fan which has 3 lights in it. I am constantly replacing the same bulb,
>the other two have only once needed replacing. I had thought that it
>was the fixture or the wiring but... another light in our house burns
>out unbelievably fast, and in that room we not only replaced the fixture
>but had it rewired completely when we renovated and that room is now on
>its own circuit. Yet it still burns out within a month.
The fan may be just enough off balance that is vibrates imperceptibly.
The constant vibration can affect the filament. Heavy duty service
bulbs have a stronger filament to counteract this.
The other situation could be similar, depending what is near the bulb
- clotheswasher, dryer, fan -
There is a store called "Lightbulbs Unlimited" in Ft. Lauderdale and
North Miami that stocks every lightbulb you can think of, and then
some. Sorry, don't know their number.
Dave Garland
D> From: Dreamer <dre...@spamfreehotmail.com>
D> Why is it that
D> some bulbs burn out faster than others? I am thinking
D> specifically of my ceiling fan which has 3 lights in it. I
D> am constantly replacing the same bulb,
Perhaps that one socket vibrates more. Vibration/shock will kill bulbs.
Try using "rough service" bulbs or bulbs specifically sold for ceiling
fans.
-Dave