Need some illumination

There is some disagreement over on the wiki article :
http://wiki.diyfaq.org.uk/index.php?title=Dimmers_%26_Switchbanks&oldidP04
Mostly covered in the Stanley Unwin section here:
http://wiki.diyfaq.org.uk/index.php?title=Talk:Dimmers_%26_Switchbanks
On the subject of energy efficiency, NT and I have a difference of opinion:
The words as I left them in the intro said:
"The pros and cons of switchbank lighting versus dimmer control will vary depending on use patterns. For users who typically use maximum brightness, then neither technique will save much energy, although dimming will have a slight edge since it will tend to extend bulb life a little (and hence re-lamping costs) by virtue of the slight reduction in maximum brightness that is usually enforced.
For users who routinely use less than full brightness illumination, the energy saving potential of a switchbank is far greater. "
The new wording says:
"The pros and cons of switchbank lighting versus dimmer control will vary depending on use patterns. For users who nearly always use maximum brightness, neither technique will save much energy.
Dimmers at full brightness have a slight energy efficiency disadvantage since the triac voltage drop will run the lamps at very slightly lower rms voltage and efficiency, but the amount of the effect is trivial. This does also extend lamp life by a trivial amount, with a tiny consequent saving on bulb manufacturing energy, but this is much smaller in size than the energy efficiency reduction due to operating at slightly lower rms voltage. In all these effects are trivial. "
To me this seems somewhat complex and perhaps a little obtuse.
Any thoughts on better wording?
--
Cheers,

John.

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John Rumm wrote:

I think the effects of dimmers at full brightness is sufficiently trivial not to need addressing at all. I responded on that only because you introduced the question of its effects.
You seem not to realise that there is any way a dimmer can increase electricity consumption compared to the other options. In fact there are a few ways it sometimes occurs.
A. Usually what people do when they want lower lighting level is switch the main light(s) off and use other lower power lights. This means those lights run at max energy efficiency. Using a dimmer instead runs more lights at much reduced efficiency, thus eating more power for a given lighting level compared to the other real world options. Thus fitting a dimmer for people that already do this will increase their energy use, not reduce it.
B. Dimmers preclude use of CFLs. Some people do and will use CFLs, so again dimmers sometimes force filament lamp use with their 3 or more times as much energy use.
C. Since the ideal lighting arrangement provides at least 3 levels: standard, reduced for comfort, and higher brightness for detailed cleaning etc, some people who use a dimmer will fit enough wattage to cater for max output and spend a lot of time running them slightly dimmed. Electricity consumption rises significantly due to this, as was explained until you edited it out.
To assume that fitting a dimmer will reduce your energy use is just plain wrong. If we're going to put the time into writing articles, really they need to have some degree of expertise to them rather than being repetition of popular notions.
- On which matter I'm guilty when it comes to the sand article. No-one seems to have raised the bar on that one yet. http://www.wiki.diyfaq.org.uk/index.php?title=Sand
2. If I understand you you think reducing energy efficiency with a 1.5v drop will reduce household energy consumption, when IRL sometimes people will accept lower use and sometimes they will say no, too dim and put bigger bulbs in. You're not going to lower average power consumption by reducing energy efficiency. The energy saved by the trivial extension of bulb life does not make up for this, as you'd know if you understood why GLS lighting has 1000hr mean life.
TBH the article needs a good rearrangement so that the issues can fit the heading framework sensibly, and I think for once you could do with being a bit clearer on this subject before editing this one. I can quite accept the article needs work, thats how wikis go, but removing valid content that perhaps needs wording more clearly and inserting common misunderstandings isnt helping us to get it there.
NT
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snipped-for-privacy@care2.com wrote:

Filament lamp life is inversely proportional to something like the 12th or 13th power of the applied voltage IIRC. Hence a small swing of a few volt can make a substantial difference to life (as if often observable in properties where there is a high (but just in spec) mains voltage).

I think you will find I spelt that out quite clearly and provided figures to illustrate it when I added all the extra detailed calculations.
What I was saying however is that in the *absence of any other changes*, the replacement of a switch with a dimmer will not increase power consumption. Therefore there is no particular reason to discourage people from doing so with warnings of reduction in energy efficiency (with the easily mis-read implication that means using more energy)
I also fully accept that compared to using a switchbank or CFL or optimising you bulb sizes it will not save anything like as much.

Again, something mentioned in there already. However you have to allow for all the various patterns of use and not just assume the way some people do it is universal.

Which is covered by "For users who routinely use less than full brightness illumination, the energy saving potential of a switchbank is far greater." and various other parts of the article.

I think these are also already covered in the article.

In the specific example given, and in the part of the article we are talking about (like for like swap of a switch, no other changes, lamps run typically at full brightness), it was self evidently right. Hence my concern over it being changed.
> If we're going to put the time into writing articles,

By the same token, having an article read like a "I don't like dimmer switches, and hence will say anything I can to put you off them" does not help much either.
In much the same way as I did not promote the inability to use a CFL on a dimmer as an advantage. I may not like any of the CFLs I have tried so far, but plenty are happy enough with them.

I agree that if you change for a bigger bulb and run it dimmed to the previous illumination level then obviously you use more. The sums show this clearly.
If you don't change the bulb however, and save a couple of watts on power consumption, plus you get a 10% lamp life increase increase resulting from the lower voltage, and another 20% from soft start ((halogens rather than GLS here) - and both figures erring on the conservative side), that is not a trivial life cycle energy saving in manufacturing, distribution, and disposal costs.

Probably true of many of them. If you look back through the history though, this one has come on in leaps and bounds over time and includes much more practical information than it used to.

I did not remove the content, just questioned it.
One of my concerns is that for an article called "Dimmers and Switchbanks" it seems to spend rather more effort talking about energy consumption issues, rather than the practical ones of creating controllable lighting levels.
How about a simplified wording for that section that says :
"The pros and cons of switchbank lighting versus dimmer control will vary depending on use patterns. For users who typically use maximum brightness, then neither technique will save much energy. For users who routinely use less than full brightness illumination, the energy saving potential of a switchbank is far greater. "
Leaving out the tortured detail of efficiency (illumination or energy), triacs, etc since most of that is covered in other parts?
--
Cheers,

John.

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John Rumm wrote:

OK. Lets see if we can find some things we can agree on. I dont know what of the below we'll agree on, but whatever it is should make a start.
I'll address what you wrote as a separate reply.
1. Fitting a dimmer normally results in a changed pattern of lighting use (if it doesnt, there wasnt much point fitting it)
2. This means that in real life we can name 2 situations, the Before situation and the After situation. These are the lighting use patterns for each user before and after fitting a dimmer.
3. In real life the fitting of a dimmer can not be assumed to result in no other change than using it. Why? Some users fit a dimmer as they previously switched some lights off to reduce brightness, and think a dimmer would be easier, look nicer or offer a wider range of control. Some users never dimmed before but will afterwards. (There are other options as well, but another day).
4. Given the above, and a few more factors I'll skip for now, we could not realistically conclude that if a dimmer is fitted, the change will always be from a given wattage of undimmed lights to the same wattage of lights now sometimes dimmed. Of course this happens in a percentage of cases, but clearly not all.
5. If we're going to determine whether fitting a dimmer will reduce one's energy consumption, we need to compare the real world lighting use situations before and after, not just a single pair of possible and sometimes so situations.
6. Now, if we can agree that far, then we can look at the various before and after options that often happen in the real world, and see where each takes us.
Before 1: Single set of filament lighting of X watts on one switch. No plug-in lights, no switchbank, no other means of reducing lighting level ever used, and only filament lamps are ever used.
After 1a: Single circuit of filament lighting of X watts, sometimes dimmed. Result: Some energy saving.
After 1b: As 1a, but with the same brightness achieved by increasing bulb wattage and reducing the dimmer setting a little. Why would anyone do this? To enable occasional use of higher brightness, for tasks such as: - more thorough cleaning - seeing clearly behind the computer, tv, or whatever else may get things plugged in the back at times etc. - better illumination for various other purposes that people sometimes have Result: more energy used
After 1c: User wants to save energy as well as reduce brightness, and chose a dimmer without realising the benefits of other options. User would have bought a couple of plugin lamps and used those for lower lighting, but due to lack of knowledge went for the dimmer. Result: Less energy use than previously, but more energy use than the plugin option that sometimes would have been chosen if the knowledge had been there.
After 1d: A year later user decides to go over to CFLs, for any of a few possible reasons. Dimmer prevents this, thus while it may or may not have saved some energy initially, it now results in 3x as much energy use as would occur with no dimmer.
There is also another Before possibility, that the user used to leave a kitchen light on to light lounge while in lounge, but now uses dimmed lounge lighting. Result: more energy consumption.
Another real world Before situation we have to consider, and its a common one:
Before 2: Lighting on 2 or more switches, which are sometimes switched so as to produce dimmer illumination. This is common in long rooms, domestic corridors and many other rooms, where lighting is not intentionally designed for dimming by switchbank, but partial lighting area overlap means that this basic approach to reduced lighting level is sometimes used.
In this situation, fitting and use of dimmers will in most cases increase energy use. I assume I dont need to go over each possible After situation to show this.
Before 3: Plug-in lights as well as fitted lights, with the combination used giving more than one brightness level.
The result of fitting a dimmer with this one will be the same as the above 'Before 2', in the majority of cases more energy use.
Before 4: a set of kitchen lighting was too bright for much of the time, but all on one switch. So the lights were left with some on and some individually switched off (or with dead bulbs in). One encounters this where under cabinet worktop lighting has been used to provide most of the light in a kitchen, or anywhere where the lighting installer has gotten a bit too enthusiastic.
User fits a dimmer and now runs all the lights on but dimmed a bit. Result: more energy use.
Etc etc. The conclusion we can draw is that while dimmers sometimes reduce energy use, they also sometimes result in more energy use.
All of these options occur in the real world. There is no way one could realistically conclude that fitting a dimmer will consistently save energy. The problem with some of what has been written before is that it strongly appears to imply that a dimmer will save energy, which is often not true.
I can see one possible way forward with this. That is to remove all mention of energy efficiency from most of the article, put it under its own 'Energy Efficiency' heading, and mention all the possible scenarios above, so the end user knows that in some cases they will save energy, and in some use more.
Are we finding some areas of agreement?
NT
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snipped-for-privacy@care2.com wrote:

Agreed
At its simplest level it means the brightness will be turned down some of the time....

Yup
Indeed true, but missing my point really. All I was saying is that fitting a dimmer in the absence of any other changes - i.e. same bulb, same on time, but now some of the on time will be at reduced brightness, will not result in increased energy usage.
For many users of dimmers that I have observed this is a typical mode of use. Not all certainly, but it would be misleading to imply that costs will rise if you fit a dimmer and this is your usage profile.
For example, I have a remote control touch dimmer in my office - almost all the time it is on full brightness. It allows me to turn the lights on when it starts getting hard to see without interrupting what I am doing, and it lets me dim the lights if I decide to take a break and watch a movie on the computer.

Indeed. And my comments applied just to this one case.

The figures we have so far illustrate:
Filament, Full Power, No Control      Filament, Full Power, Dimmer      Filament, Optimal Power, No Control Filament, Switch Bank
What others would you like?
We could add "optimal power, dimmer" to those which would show a very slightly lower cost than the optimal power no control figures.
The situation you frequently mention(i.e. fitting a bigger bulb then dimming) is covered by the Full Power, Dimmer option. This shows a slight energy saving over having the same bulb and just a switch, but it is also contrasted as 50% more expensive than the switchbank solution.

Yup agreed (in our figures already)

Agreed (in our figures already)

No necessarily lack of knowledge... they may just not like table lamps etc.

Agreed - with the above proviso. You may accept the higher cost in exchange for the simplicity and lack of clutter.
(personally I am not so keen on table lamps because inevitably you end up looking at them which is not always comfortable - I can never deduce the logic of people who stick a table lamp on or beside a TV for example - you spend the whole trying to watch a program with a bright light in your peripheral vision).

Seems like a non issue to me. You just replace the switch.
However this point is included in the article already.

Depends on what the kitchen light is presumably - if the kitchen has 400W of halogen downlighters then it could equally save money.
There does not seem to be much point in providing figures for obscure uses like this since there is an infinite number of them.

If there is little or no overlap in regions then they would typically have to use both, so the dimmed solution will cost slight less. Only if they switch from one light to two dimmed lights would it increase.
I think once one has made the point that running dimmed lights will cost significantly more than switching some off, all these cases can be left for the reader to work out for themselves.

Again this is just conjecture. The logic may equally be - "oh the top light is brighter than we need with the table lamps on", fit a dimmer. This will save a little, but less than sticking a smaller bulb in the top lamp.

We already cover this situation in the figures. Full Power, Dimmed, Vs Full Power Switchbank (in fact we need to include the "full power" text in the table for this one).

Yup agree fully.
So why the difficulty in highlighting the cases where they will save money? Since we also cover the cases where they won't.

I never said it did. I seem to recall that the para you wanted to "enhance" with talk of triacs and negligible efficiency etc was simply one that said (paraphrasing), "if you use the lights on full power most of the time, neither dimming or switching will save much, but you may get a slight advantage on a dimmer with longer bulb life". (paraphrasing)

Well the figures already show the dimmer costing 50% more than the other filament options (with exception of running full power lights flat out on a switch).

I think we agree on pretty much all of it. I just had problem with the words "Dimmers at full brightness have a slight energy efficiency disadvantage since the triac voltage drop will run the lamps at very slightly lower rms voltage and efficiency, but the amount of the effect is trivial." - given this was in the section that discussed using lamps on full brightness most of the time.
It is a very complicated way of not making any real sense. Using phrases like "energy efficiency disadvantage" would to most people I expect be interpreted costs more, rather than "costs a little bit less unless you compensate for the reduction in bulb brightness by using a bigger lamp in which case it will cost a fair bit more"
The other point I wanted to introduce somewhere was the potential benefit of soft starting on halogens since this can represent a worthwhile increase in lamp life (and hence life cycle energy costs)
--
Cheers,

John.

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John Rumm wrote:

The writer appears to be suggesting that the triac V_drop will result in saved energy. This is a classic false argument. Maybe more on that later though, there are bigger issues here.

FWIW 1.5v drop is apx 1.5v rms drop, so from 240 nominally to 238.5v. Thats 0.625% Vdrop.
For a standard GLS lamp, life/life = (volts/volts)^13 efficacy/efficacy = (volts/volts)^1.9
So 0.625% V_drop gets us: 8% longer life, or 1080 hours 1.2% reduction in efficacy
Both are small enough to be lost in the noise.
However, we may as well leave this trivial stuff out for now.

I cant agree. What has been said appears to me to imply otherwise.

Problem is that isnt the real world situation. It isnt what happens in a lot of cases. We need to look at the real world comparison(s) instead of just one possible scenario.

people from doing so
Its not about encouraging or discouraging, it doesnt make any difference to me what people install, and I imagine not to you either. Just a case of getting the facts clear, then we wont end up covering the same ground over and over in the newsgroup.

I dont think stating the facts about energy efficiency is a 'warning' its just letting people know what the options and results are. Because some pepople do care about it.

Some of the time fitting a dimmer does. Thats the point.

What makes you think it will save at all?

for all the various patterns of use and not just assume > the way some people do it is universal.
that is precisely what I'm saying!

That doesnt convey the relevant info at all, and really is misleading I think. It seems to imply some energy saving will occur with a dimmer, which is not a true statement.

If theres one thing thats self evident here (imho), its that that is often _not_ what happens when people put dimmers in. Of course you can describe that one possibility so, but to conclude from that that installing a dimmer will save energy is simply wrong.

This is your inference, not my statement or implication. If we just stick to the facts and get them right the question doesnt arise.

no, its not a saving at all, its an increase. Taking filament bulbs even further away from their ideal operating point is not going to save energy!
I mentioned this, but didnt explain it, when I talked about why bulbs are rated for 1000 hrs. The ideal cost & energy efficiency point for GLS lamps is somewhere in the region of 300 hour life, but people dont want such short lived lamps. 1000 hour bulbs run some distance away from their ideal cost & energy efficiency operating point, and taking them even further away from this point makes matters worse. IOW the cost and energy saved from longer lamp life is smaller than the cost and energy burden caused by running at lower energy efficiency.
Its no use saying one can trim a bit off output and no-one will notice, the reality is that many will stay with the same bulbs and a few will uprate the wattage, and you dont get any mean energy saving. The more you trim down the light output, the more % of users will uprate their bulb wattage. You really dont save energy by reducing energy efficiency.
If users want a given level of illumination, energy use is minimised by providing it at higher efficiency rather than lower. The notion that you can trim the lighting level and no-one will do anything about it is a false one, which I could explain more if necessary.
Filament bulb cost and manufacture energy are both small compared to run cost and energy use, and the purchase cost deltas are smaller than the run cost deltas as you move a GLS lamp's operating point.
Oh why not.
100w GLS: purchase cost 20p per 1000 hours Run cost 10 per 1000 hrs
50w 1500hr halogen: purchase cost 50p per 1500hrs = 37p per 1000 hrs Run cost 5 per 1000 hrs.
For the halogen: 8% life extension would save you 2.9p in purchase costs per 1000 hrs. 1.2% efficacy reduction would add (for a given total light output level) 6p per 1000 hours.

I'm inclined to agree. There is a lot more conceptually to energy efficiency than any other aspect of it, the rest is pretty simple. Perhaps it would be a good idea to put energy efficiency under its own separate heading, so those that arent interested wont need to wade through any of it.

Its misleading because it implies a dimmer will save you energy.
NT
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snipped-for-privacy@care2.com wrote:

The suggestion is the saving will come from lower relamping costs.

So 8% for that, plus some more for soft starting, and we can live with the reduced max brightness, so the efficacy change is neither here or there.

If you are daft enough to fit mains halogens you may not think so if it means you can buy 25% fewer bulbs.

Well suggest extra figures to add to the comparisons then.

It is *a* real world situation - not the only one, but real none the less.

This may also be true, but does not negate the first option.

In the context of the quote though (and in particular with the way it was worded) it created the impression that it would lead to higher energy costs when one is simply doing a switch swap and using the same lamps for the same hours. In this circumstance at worst it is going to cost the same.

Agreed, but don't stick the comments on this in a section talking about a case where this is not the case.
The article as a whole makes the point quite well in favour of switchbanks with regard to energy use anyway - it does not need to do it in every paragraph.

Slight reduction in power dissipation, some increase in bulb life - possibly significant with soft start on halogens.

Compared to using full brightness all the time, use of a dimmer *will* save some energy.
According to the sums on the page:
Filament, Full Power, No Control      76      1,920 Filament, Full Power, Dimmer     60     1,505 Filament, Switch Bank      36      903
Which seems to match the statement in the text quite nicely.

I agree. The conclusion was however more specific, namely: that in the specific case of using full power lighting with the same usage pattern, having it dimmed some of the time will save energy.

Depends on how you spin the facts does it not?

Now here is the bit I can't follow.....
You are using less electricity and buying fewer bulbs. I can't see how that is an increase.
In exchange for these savings your sacrifice some light output when you want maximum illumination.
The only way I can see that you may incur extra costs is if you increase the bulb power at the same time. Otherwise the switch is in series with the bulb, and Mr. Kirchoff might have issues if you want to claim that current flow will increase.

None of this really has any real world bearing. It assumes that people will compensate for the reducing light output by turning on other lights they just happen to have wired in and ready to go, to make up the difference - recovering the reduction in brightness. I have never seen anyone do this. You may change the bulb sooner if it becomes too much of a problem, but installing extra lights?

Chances are you won't. Your eyes have an exponential response to brightness and a built in brightness control mechanism. You may notice a step change of a couple of volts if it happens when a lamp is on. However as a gradual change or in discrete instalments you are unlikely to see a change.
As you already said, we use filament lamps (and CFLs in fact) well past their hours of brightest output. I have a hard time believing that a sizeable proportion of people replace them at any time other than when they fail.

Appart from when you accept the lower output as part of the package.

Agreed.
You are flogging a dead horse here, so don't bother.
OK, group poll - will post in a separate thread...

Back to the same old fallacy that one turns on more lamps to compensate for diminishing brightness.

Don't forget the extra 25 - 100% soft start savings. You are also assuming that you never use the dimmer to reduce the brightness here.

Yup, I would go for that. In fact an much bigger scope article on energy saving in the home might be useful. Helps put these things in context. It all well and good claiming you can save 1000 over 25 years with your choice of lighting, but may well pale into insignificance if you are loosing that much per year due to drafts and poor insulation.

Which in that limited context it would (unless you want to get into the hypothetical wiring up of more lamps to compensate for reduced light output over the extended lifetime of the bulb).
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John.

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John Rumm wrote:
I'll keep it fairly brief.

for mains halogens yes, for other lamps no significant gain. So that would gain us what, 25% of 37p is 9p. But 0p for other types.

I think now the remaining issue is that of explaining what we both agree on, or wording for the article. It should not be too hard in principle to come up with something, even if we go back and forth 2 or 3 times.
A very simple way to get that ball rolling could be to say that changing to a dimmer will in some situations save energy, and in some use more, and give a link to this thread for more info.

your mind reading module may be less accurate than you think.
I think the repetition of relative energy efficiency came about because of the layout more than anything else. The layout doesnt seem to work that well.

Those points I fully agree with, but none of them change anything. IOW I wasnt writing in ignorance of the above.

I'm not clear how you get to there from anything I've said or youve said, and so far its only each other's statements we've been discussing here.

Far from it, this is standard stuff.
Lets tackle it with a reductio ad absurdam.
You say you wont notice a 0.625% Vdrop. (I agree with that much.) Now, if thats true, if people dont notice going from 100% to 99.375% , they also wont notice the same step change applied again, ie from .625% down to 1.25% down. Its exactly the same magnitude of change.
We can confirm this with an experiment, and I think we can run this one as a thought experiment. We lead people into a room lit at 100% or 99.375%, let them see it several times, without knowing which are which, and ask them to tell us which times were 100% and which were down 0.625%. I expect we'll agree that people wont pick it up with any notieable degree of reliability.
So, lets run ad absurdam with your hypothesis now. You make a small step change, no-one notices. Next day you make another small step change, again noone notices the step change. You keep doing this day by day, and no-one picks up any of the step changes. But according to me, somewhere along the line they say hey, the lighting isnt very good, we need to up the bulbs in here. According to your hypothesis, the lights will go completely out and they still havent noticed. I know thats not what you said, but its what follows from it by applying your argument repeatedly.
Its not hard to see that as we keep doing those step changes, most people will uprate their bulbs at some point along the line. Where it happens is spread out. The more you drop it by, the more people uprate. The less, the less.
People have a target lighting level, what looks ok to them, which varies from person to person, and they will pick whatever lighting reaches this level. This is why a lot wont change anything if you drop light output 10% - but some will. The more you drop it, the more people uprate.
Lets take it the other way to llustrate the deal - and this is one experiment I have done (though only with 2 subjects, not lots). Lets say instead of reducing efficacy we increase it. We run GLS lamps on a boost transformer so they put out more light and eat more power each. Efficacy also goes up. What do people do? They reduce the bulb wattage fitted. We both did, the increased light level wasnt needed in either case so we both dropped the rated bulb power in use (ie changed from 100w to 60w (me) and 75w (other person)). So instead of a 100w lamp I now had a 60w rated lamp running at IIRC 66w, and producing similar light output.
Lamp life is shortened, but the extra cost this incurs is less than the money saved on running energy.
If we want to improve energy use we would need to _increase_ GLS lamp voltage, which is easily done, and then replace 100w lamps with 75w or 60w ones. Its not hard to do, the downside of reduced lamp life makes it not worth bothering for most people. There are still significant saving there, as the lamp purchase cost delta is much smaller than the run cost delta.
Sometimes small effects are hard to observe clearly. If you magnify them you can see the trend and see whats going on clearly.

Absolutely. I know theres a link on the wiki to such a thread, no-one's written it up so far.
We'll get there.
NT
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snipped-for-privacy@care2.com wrote:

TLC do GU10 4000 hour mains halogens at 3.85+VAT. So the costs are a bit more on decent bulbs. (some of the elcheapo supermarket ones you will indeed be lucky to get 1k hours, but they are a false economy anyway).
A 25% lifespan increase on a 4000 hour bulb is also not insignificant.

Yup, works for me.

I think that will be helped by shifting the detail of the energy saving aspects to a dedicated energy saving article, so as to leave this one focussed on practical stuff to do with lighting level control etc.

Well if you follow the argument about reducing energy efficiency (in lumens/watt) costing more to run. It can only cost more to run if you somehow compensate for the reduction in light output. There are only really two ways you could compensate for a dimming bulb - replace it or supplement with others. I think most people just accept it. If they notice it at all it is at the point where they replace it and think "oh, that is a bit brighter"
(anecdotal story that is a good example of that. My bathroom had the sunken spotlights that each took a 60W R80 bulb. As far as I could tell the bulbs were ordinary Sylvana R80 ES lamps. However they came with the house (hence no idea what their installed hours were), and all three much to my amazement carried on for a further 10 years! Only when one finally failed and I replaced it did I notice that the new one was noticeably brighter than the remaining two - a far more marked difference than in any of the other three spot fittings we have that typically have much more conservative bulb lives. However prior to a bulb failing, I never felt that the lights were dim or in any way inadequate).

As an incremental change this is probably true. As you go further down the volts, the loss of lumens per volt will increase though - so at some point you would notice.

yup
Well not quite. I tend to find that you don't reach the point of "hey, the lighting isnt very good" within a typical or even extended lifetime of the bulb. Note my extreme example above. More conventionally, had I say bought a 4000 hour halogen, and actually got 5000 hours out of it, I don't expect the lower performance in those last 1000 hours would be a problem.

In theory yes, but I don't see this happening. Which suggests to me that they are not falling far enough down the efficiency curve to make it an issue.
(also bear in mind that most filament lamps are flash stressed at the time of manufacture to help ensure they fail before they get too far into their dotage)

Yup, agreed. So one pertinent question is then, for those who do something with a lamp that causes it to last much longer than its "normal" life, how many are going to reach a point where its output is no longer acceptable due to ageing of the bulb?

So long as you ignore the energy costs of procuring, transporting, fitting, and disposing of the extra bulbs and also ignore the costs in your time, this would probably be more attractive.

Indeed, I am sure most people can do far more productive things with their time.

Yup, but less so when you add back in all the overhead costs (money and energy) in keeping up with the increased re-lamping rate.

Perhaps a "Energy saving" article would be good - but I can see that creating more heat than light on occasion!
--
Cheers,

John.

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John Rumm wrote:

An extra 1000hrs, shofting purchase cost from 1.13 per 1000 hrs to 90p per 1000 hrs, so 23p per 1000 hrs. But if anyone buys such bulbs I would question if it were a good move.
I shant go over the rest, some I agree on some I dont, but I think it shouldnt be hard to come up with a revised article that we all agree is sound and addresses the significant issues.
NT
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Seems to me that if you need advice on how to give advice on something that you purport to have some knowledge then you should leave well alone and leave it to those who know what they a talking about.
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