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    Leaving fluorescent lights switched on at home…
    • #1
    • 13th Oct 04, 6:46 PM
    Leaving fluorescent lights switched on at home… 13th Oct 04 at 6:46 PM
    Leaving fluorescent lights switched on at home…


    Now, I know as good Money Savers we should all be leaving lights switched off at home whenever we leave the room.

    However, I remember being told a long long time ago that fluorescent lighting uses more energy when it is being switched on that than it does for it to be kept running for a number of hours, is this correct or an urban myth?

    If you are going to go back into the room within a hour it is cheaper to leave it switched on, is this correct or a old wives tale?!

Page 1
  • loon
    • #2
    • 13th Oct 04, 7:55 PM
    Re: Leaving fluorescent lights switched on at home
    • #2
    • 13th Oct 04, 7:55 PM
    if you are referring to the low energy lightbulbs... you are correct. because they take a while to warm up, they do work out cheaper if you leave them on; that is to say, do not put them in light sockets that are only turned on for a short while. eg. toilets, cupboards, etc.
    • mrcow
    • By mrcow 13th Oct 04, 8:28 PM
    • 14,427 Posts
    • 30,435 Thanks
    • #3
    • 13th Oct 04, 8:28 PM
    Re: Leaving fluorescent lights switched on at home
    • #3
    • 13th Oct 04, 8:28 PM
    The below may help?

    I've also read that with "normal" lightbulbs, if you are leaving the room for more than 3 seconds, then it's worth turning them off - this jumps to 5 seconds with energy saving lightbulbs.

    Should I Turn Off Fluorescent Lighting When Leaving A Room?

    Short Answer: Turn them off if you will be gone for more than about 15-20 minutes (for details keep reading).

    There are a few misconceptions about fluorescent lighting that keep too many people from turning lights off to save energy. The first misconception is that it takes more energy to start a fluorescent light than it takes to run it. The second misconception is that turning a fluorescent light off and on will wear it out right away. Like many of our myths about energy, there is a small amount of truth in the belief. (Special thanks to Steve Selkowitz of Lawrence Berkeley National Labs for doing the research that this article is based on.)

    Misconception #1: It takes more energy to start a fluorescent that it does to run it, so leave the lights on all the time to save money on your electric bill.

    Reality: When you turn on a fluorescent light bulb (correctly called a "lamp&quot, there is a very brief jump in current when the ballast charges the cathodes and causes the lamp to start. This inrush of current can be many times greater than the normal operating current of the lamp. However, the spike of current draw normally lasts no longer than 1/10th of a second, and draws the equivalent of about 5 seconds of normal operation. So, if you turn your fluorescent lamp off and on more frequently than every 5 seconds, you will use more power than normal. So, normal switching of fluorescent lamps has very, very, very little effect on a power bill.

    Misconception #2: Turning fluorescent lamps off and on wears them out right away.

    Reality: Electric lights have a published rating for expected life. This rating is in the hundreds of hours for many incandescent lights, and in the thousands of hours for most fluorescents. Fluorescent lights have a life rating based on how many hours they are left on every time they are turned on. This is usually referred to as "burn time", and for fluorescent lights the burn time is three hours.

    Every time a fluorescent light is turned on, a tiny amount of the coating on the electrodes is burned off. Eventually, enough coating is burned off, and the lamp fails to start. Most full-size fluorescent lamps are rated to last 20,000 hours when left on for 3 hours every time they are turned on. This means that the lamp has roughly 6,667 starts available to use up. (20,000/3 = 6,667)

    Longer burns extend lamp life. If you "burn" your fluorescent lamps shorter than 3 hours per start, you use up your potential starts faster. If you "burn" them longer than 3 hours per start, you use up your starts more slowly. However, you are paying energy costs for the operating time of the lamps, and the most efficient lamp is the one that is not on when it is not needed. See Table 2 for the effects of longer burn time on lamp life.

    But longer burns use more energy. Operating a light when it is not needed is simply spending money for no purpose. Today's rapidly rising electric rates mandate that every building becomes leaner with energy use to control costs. See Table 3 for a comparison of operating costs for a typical fixture.

    Find the trade off point.
    There is a point where the amount of money you save from turning off the light exceeds the cost of reducing lamp life by more frequent starts. If you use the formula in Table 1 at $0.05 KWh, you come up with a time of about 15 to 20 minutes for that point. As energy rates go higher, that time becomes shorter. If you pay less than a nickel per kilowatt hour, your turning-off point would be longer.

    The kind of ballast you use may make a difference if you turn your fluorescent lights off frequently. There are three different kinds of electronic ballasts: instant start; rapid start; and programmed start. Which one you use can influence your choice of how frequently to switch off your fluorescent lights. Check with your ballast supplier, or contact a lighting specialist at the Lighting Design Lab for more information on different types of ballasts.

    Table 1:
    The "Official Formula" to calculate how often to switch lamps off and on

    In "Economics of Switching Fluorescent Lamps" IEEE Transactions on Industry Applications Vol 24, No 3, May/June 1988, Carriere & Rea provide a function f(u), that describes the lamp life in burning hours relative the rated lamp life under that standard burning cycle of 3 hours lamp operation per start.

    Actual Lamp Life =
    Rated Lamp Life x f(u) where, f(u) =
    1.71 (1-exp[-(u/3.89)^0.505]) u =
    burning cycle, hours of operation per start

    Table 2: Burn hours and Fluorescent Lamp Life for a Typical 4-foot Rapid Start Lamp (32W)
    3 hr 6 hr 12 hr 24 hr
    20,000 24,000 28,000 34,000

    Table 3: Comparative annual operating costs for a 3-lamp T-8 fixture with electronic ballast (94W) (@$0.05/kWh)
    Burn Time
    per day Annual
    Hours Annual
    3 hrs 1095 $5.15
    6 hrs 2190 $10.29
    12 hrs 4380 $20.59
    24 hrs 8760 $41.17

    Taken from:

    Unfortunately it's a US site, so the calculations are in USD.

    Hope this helps?
  • Loch37408
    • #4
    • 14th Oct 04, 11:32 AM
    Re: Leaving fluorescent lights switched on at home
    • #4
    • 14th Oct 04, 11:32 AM
    A very comprehensive reply indeed mrcow! Many thanks.

    Just for the record I am talking specifically about fluorescent strip lighting - the type commonly found in kitchens.
  • Tania
    • #5
    • 14th Oct 04, 6:26 PM
    Re: Leaving fluorescent lights switched on at home
    • #5
    • 14th Oct 04, 6:26 PM
    Thanks for that - just nipping to kitchen to turn off light. Ours is left on loads of time. Now when hubbie goes on, ill show him this thread. x
    • zcaprd7
    • By zcaprd7 21st Oct 04, 2:13 AM
    • 1,062 Posts
    • 106 Thanks
    • #6
    • 21st Oct 04, 2:13 AM
    Re: Leaving fluorescent lights switched on at home
    • #6
    • 21st Oct 04, 2:13 AM
    Heh, Heh - this is very similar to the thread on energy saving light bulbs where I argued that as all the 'wasted' heat was diffused into the surrounding area i.e. heating up the building, the (during winter at any rate) energy wasn't being wasted at all, because your heating bills would be that much lower...

    So that's 50% one can slash off the quoted energy saving rates - I was suprised that nobody questioned the fact that energy companies promote the darn things - yet more green propaganda.

    I guess they are happy for a misguided change because it raises general awareness of energy saving? !Or do they really believe it makes a big difference?
  • Marga
    • #7
    • 21st Oct 04, 12:46 PM
    Re: Leaving fluorescent lights switched on at home
    • #7
    • 21st Oct 04, 12:46 PM

    Errrr......if I can just interrupt a minute? Can anyone tell me the score with those silly halogen lights? I was recently foolish enough to buy a new light-fitting made up of those small halogen lights (do you know the ones I mean?). Anyway, the type of fitting required for them (bayonet) means the cheapest ones I seem able to buy are £2.00 each, and usually you have to buy them in packs of 6! When switched on, I'm lucky if they last a day or two. However, I have now started leaving them on all day and they seem to survive a bit longer now ( I think the first one of this batch lasted about 2 weeks using this system). Can anyone shed any light on this..........errrrr?
  • aidyonline
    • #8
    • 21st Oct 04, 12:49 PM
    Re: Leaving fluorescent lights switched on at home
    • #8
    • 21st Oct 04, 12:49 PM
    My word,

    I thought i was an angry loner til i read this pag ;D ;De!!!

    no-one dare call me a nerd again!!
    • chevalier
    • By chevalier 21st Oct 04, 1:14 PM
    • 7,761 Posts
    • 18,056 Thanks
    • #9
    • 21st Oct 04, 1:14 PM
    Re: Leaving fluorescent lights switched on at home
    • #9
    • 21st Oct 04, 1:14 PM
    Hi Marga
    If your bulbs are failing that quickly then you may have a problem with your circuit not the bulb. I would suggest that you get an electrician to check.
  • Marga
    Re: Leaving fluorescent lights switched on at home
    8) :P ! Ps......LIGHTEN UP EVERYONE!!!....... ;D

    Insert from Martin
    Quite right Marga - there were a few less 'enlightened' posts in this thread, which i have switched off
  • nationwide
    Re: Leaving fluorescent lights switched on at home

    I had the same problem with those small halogen lights when I had my new kitchen fitted in my last house. The electrician talked me into having that type saying it was the in thing and very cost effective, this proved to false economy.

    I ended up searching around for the cheapest deal I could find and found that Screwfix Direct was the cheapest place selling them at the time.
  • jirving
    Re: Leaving fluorescent lights switched on at home
    Yep, when I built my new extensions 4 years ago I put in small halogen fixtures that take GU/GZ10 bulbs and lifespan has been very poor. Cheapest place for bulbs at present is Wickes @ about £2 each but I'm going to take the fittings out and swap them for the SES reflector bulb fittings that might cost a little more initially but the bulbs are about 40p each.

  • sparky62
    Re: Leaving fluorescent lights switched on at home
    Halogen lights need a decent air flow/space around them, if they don't have the space to 'breath' they will blow regularly. I have also found that screwfix are the cheapest. They are also very cheap fo the watch/organiser type batteries i.e. £095 each as apposed to Boots @£3 +. If you haven't used screwfix find someone who has and if they recomend you they get a £10 voucher to could split it !!!! :
  • sjh1008
    Re: Leaving fluorescent lights switched on at home
    Anyone had a problem with these (halogen) lights that they intermittently turn themselves off, only to turn themselves on again seconds / minutes later? We have a circuit with 3 lights on, and one spends about half the time off, one about 10% off and one is mostly on. Not sure whether to look at the circuits or the bulbs?
    • Cullumpster
    • By Cullumpster 22nd Oct 04, 3:01 PM
    • 1,476 Posts
    • 826 Thanks
    Re: Leaving fluorescent lights switched on at home

    If i'm thinking of the correct bulbs (probably not knowing me !) i've got halogen bulbs in my kitchen.
    Get yourself off to the pound shop, got 2 packets of 2 about 2 months ago and they're still going strong !

  • Mattlovatt
    Re: Leaving fluorescent lights switched on at home
    This is my first time so here goes.
    Re. the halogen lights, I suffered several blown bulbs until I was told not to touch them with bare hands (especially if they are hot.....) I now fit them whilst wearing a cotton glove and as if by magic none have blown since. Not sure what the sience is behind this but it appears to work.
    Now, back to mrcow....? ???
    • fishter
    • By fishter 23rd Oct 04, 1:26 AM
    • 17 Posts
    • 8 Thanks
    Re: Leaving fluorescent lights switched on at home
    When you handle the lamp with your bare hands you leave oily deposits on the surface of the bulb. When you switch the bulb on, these oily spots get really hot and this causes the lamp to fail prematurely.

    Cotton gloves, or a couple of tissues, will stop this happening.
  • Vicky_Pollard
    Re: Leaving fluorescent lights switched on at home
    Good advice...........

    Leaving your fluorescent lights on wastes money. If you're not in the room, turn them off. Starting the lamp does damage the cathode slightly so frequent switching will affect lamp life, but this is only true of a switch start (the ones with a starter switch) or a 'cold start' HF ballast.

    If you have a starter switch in your fluorescent light, replace it for an electronic version, (such as EFS600 or LEL UM2) which is best bought from an electrical wholesaler, should cost about a quid. DIY warehouses charge the earth! This will prevent damage to the lamp when switching.

    When you buy a fluorescent light, you have a number of options.

    You may be offered :-

    1) standard switch start - cheap and best avoided.
    2) High Frequency (warm start) - lower running costs, increased lamp life but only last 50,000 hours before they need replacing.
    3) High Frequency (cold start) - lower running costs, but lamp life same as switch start, and a 50,000 hour luminaire life.
    4) Low loss ballast - Lower running costs, long life. Use in conjunction with an electronic starter for long lamp life. Ask for a B1 or B2 rated unit.

    Never operate a fluorescent fixture with a lamp that just glows at the ends, unless you have a good relationship with your local fire brigade!

    Halogen lamps?

    ok, firstly these get very hot. Its important to match the correct lamp for the fixture. Never adapt a fixture to fit a lamp.

    Secondly, always buy a branded lamp (Phillips, Osram, Sylvania, GE). The halogen lamps available cheaply come from the far east. They mostly do not have the safety aspects of the EU lamps. e.g. in-line fuses, low pressure designs so they dont explode in your face. They also have lower light outputs.

    Honestly, if you are reading this because you wish to save money, what are you doing buying a halogen light anyway? They are notoriously expensive to run and maintain, lamp life is very poor and lamps are expensive.

    In answer to the question regarding lamps going off and coming back on again, most cheap halogen lamps will be run from a cheap 'far east' switch mode power supply. Typically these could flash - a mismatch in the transistor output, or cycle - go on and off as the transformer overheats and cools.

    Hope this has helped.

  • archived user
    Re: Leaving fluorescent lights switched on at home
    Thanks Vicky, i for one found your post useful.
  • Sybarite
    My entire flat has GU10 Halogen bulbs, about 36 in total, and I would never recommend them. They seem to be being fitted in every new build at the moment and my speculation is that they'll all be being removed in a few years time after everyone is thoroughly sick of them. At 50w each and 4-6 bulbs in a room they are phenomenally expensive after a few hours of use.

    As mentioned earlier in this thread - although I'm not sure about the green propaganda comment - the heat given off is a real problem, it may be beneficial in winter if you happen to like heating your ceiling, but it isn't really very useful during the height of summer. The shadowing, expense of buying and running them together with the heat, does make me wonder who exactly thought this was a good idea in the first place.

    I've started replacing the halogens with the energy efficient flourescent and LED varieties, which initially is very expensive thing to do but they are rated at 50 000 - 70 000 hours it should just about be cheaper in the end. The cost is shocking though, the ones I use are £8-10 each, the cheapest I've found, so £288 - £360 if I want to fit the whole flat, eek.

    On a more general point, and forgive me if it alteady exists and i'm not aware of it, it would be nice to see a dedicated 'green money saving board' as comsuming less and the moneysaving ethos seem to me to naturally coincide.

    I've used the board quite a bit and have benefited from the posts on discounted consumer durables, 0% credit cards and energy supply costs, all of which have resulted in a healthier bank balance and for which I'm extremely grateful to the members who post notices and the existence of the site. However by far and away my largest household bill after tax is electricity, which I regularly check using Uswitch etc. What I'd really like to do and what I'm wondering if anyone can offer advise on, is install home micro-electricity generators running from solar and wind. At present as I don't own my own flat I'm not able to do this, but I'm planning to buy later in the year and would like as near to a £0 energy bill as I'm able to have, with the possibility of feeding back into the grid during the night time.

    I'm actually quite shocked at how bad in terms of energy efficicent newly built houses are. My current accommodation is about 3 years old, everything is electric - don't get me started on the underfloor ceiling and floor heating - and the energy bill is enormous, the first year just under 1K. It's gone down since I became more aware of the cost, but is still more than seems reasonable. Yet the building has a large roof area and lots of scope for green generation or improvements -it's simply that as the whole block was built to let, so it's a 'machine for making the land pay' and consequently there's no interest or incentive to install anything of this nature.

    While I wouldn't consider myself a green fundamentalist, it seems irrational not to build dwellings that use as little energy as possible if technology enables you to do so. I recognise installing a turbine of solar panels will cost me a few thousand, but if they add to the property value, decrease my energy bills and have a reasonable longevity (irrespective of the environmental benefits) surely this is the logical long term choice, rather than being at the whim of energy generators' tarrifs or shelling out my part of the several billion £ in taxation that will otherwise be spent on new power stations?

    I'd love to know if anyone has ventured down this path and tried to make their home as zero emission friendly as possible? Oh and in the meantime a cheap reliable supplier of Energy efficient GU10 bulbs would be greatly appreciated.

    I do hope you're telling the truth?
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