John Rumm wrote:
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.
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).
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.
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.
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
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.
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.
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.
B. Dimmers preclude use of CFLs. Some people do and will use
C. Since the ideal lighting arrangement provides at least 3 levels:
I think these are also already covered in the article.
To assume that fitting a dimmer will reduce your energy use is just
plain wrong.
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,
really
they need to have some degree of expertise to them rather than
being repetition of popular notions.
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.
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.
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.
TBH the article needs a good rearrangement so that the issues
can fit the heading framework sensibly, and I think for once you
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.
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.
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?
"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.
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.
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).
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.
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.
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.
I cant agree. What has been said appears to me to imply otherwise.
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.
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.
Therefore there is no particular reason to discourage
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.
with warnings of reduction in energy efficiency
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.
(with the easily mis-read implication that means using more energy)
Some of the time fitting a dimmer does. Thats the point.
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.
What makes you think it will save at all?
However you have to allow
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!
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.
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.
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.
To assume that fitting a dimmer will reduce your energy use is just
plain wrong.
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.
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.
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.
This is your inference, not my statement or implication. If we just
stick to the facts and get them right the question doesnt arise.
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.
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.
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.
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.
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. "
Its misleading because it implies a dimmer will save you energy.
NT