Talk:Dimmers & Switchbanks

Pulled running cost stuff out - keeping here for the mo

Examples

Run cost and energy use depend on what amount and type of lighting is used at what setting for how long, so is a very variable figure.

This section will compare lighting energy use for a hypothetical room that is equipped with 300W of filament lighting or the approximate equivalent of 100W of CFL lighting. For this example we will use a daily use pattern of:

• 1 hour a day of 40w filament equivalent output
• 5 hours a day of 150w filament equivalent output
• 1 hour a day of 300w filament equivalent output (i.e. full brightness)

Prices are given for 10p/unit electricity cost.

No Control

Firstly the no control option, for which we will like most typical householders, have to select the wattage best suited to all round use, in this case 150w since that is the most common lighting level required. This is a compromise since we cant have the levels we really want some of the time, so comfort and utility are not optimal.

7 hours at 150W = 1.05kWh / day = £38 pa = £960 per 25 yr installation life.

If we really must have the full brightness option, then obviously the costs above will double. A more realistic option might be to provide additional table lights etc and keep the main lighting at a more conservative level.

If we opted for 50w of CFL instead:

7 hours at 50W = 0.35kWh / day = £13 pa = £319 per 25 yr installation life.

Switchbank

A total of 300W of filament lamps on switchbank will use: 1 hour at 40w = 0.04kwh + 5 hours at 150w = 0.75kwh + 1 hour at 300w = 0.2kwh

Total usage = 0.99kwh/day = £36 / year or £903 per 25 yr installation life.

CFL Lamps on switchbank will use: 0.015 + 5 x 0.8 + 0.1 kWh = 0.195kWh / day = £7 / year = £177 per 25 yr installation life.

Dimmer

For 300w of halogen on a dimmer: we will assume to get 40w equivalent brightness we run at 50% full current, and for 150w brightness we use 80% of full power

0.5 x 300 + 5 x 0.8 x 300 + 300 = 1.65kwh / day = £60 / year = £1,505 over 25 years

Energy Efficiency Summary

Lighting and control Total cost / year Total cost / 25 years
CFL, Full Power No Control £26 £638
CFL, Optimal Power, No Control £13 £319
CFL, Switch Bank £7 £177
CFLs on dimmer n/a n/a
Filament, Full Power, No Control £76 £1,920
Filament, Full Power, Dimmer £60 £1,505
Filament, Optimal Power, No Control £38 £960
Filament, Switch Bank £36 £903

Notes:

• These are costs per room
• Costs per 25 yrs are at today's prices

From this comparison table several things are seen:

1. The most expensive option is the use of full power lighting with no control. This also does not achieve the goal of controllable lighting levels.
2. Full power lighting with a dimmer is a little cheaper, but not as cheap as using optimal bulb sizing in the first place. It does however give the greatest flexibility of control over the lighting.
3. Switchbanks generally give a lower run cost than control using a dimmer, or opting for no control at all. Sometimes the cost reduction will be significant and switchbanks will pay back their extra installation cost many times over if fitted at rewire time.

--John Rumm (talk) 01:43, 7 February 2017 (UTC)

Although not my original edit, the bit about energy efficiency was probably better before you changed it ;-)

You seem to be confusing lighting efficiency with energy efficiency. A dimmer reduces lighting efficiency, i.e. you get less light per watt, but increases energy efficiency, i.e. you reduce the overall energy consumption. That fact that the fall of in light output is not proportional to this is not relevant - especially when that is the result you are seeking to achieve.

--John Rumm 00:14, 9 August 2007 (BST)

I think you may be confusing efficiency with use. Efficiency is output over input, and dimmers heavily reduce it. IOW energy efficiency is useful energy out over total energy in. The article as it stood was wrong.

As explained, they also dont reduce energy consumption, except when the question is viewed overly narrowly. When all the real world options are considered, the dimmed option uses the most energy of all.

I would have to disagree. For the VAST majority of users the choice is ordinary switch or dimmer switch. Rewiring the lights to use a switchbank won't even hit the radar. So for most real world cases a dimmer will use less power than the alternative. If you are building from scratch then by all means add extra lighting options.

--John Rumm 19:25, 9 August 2007 (BST)

So in that case the dimmer will reduce energy _use_ and reduce energy _efficiency_.

Also the conclusion you state isnt as logical as it might first appear, as there is in reality more to it. Either replacing the bulb or using a 2nd light will result in less energy use than running a dimmmed light, so it doesnt even follow that a dimmer would reduce energy _use_.

What I'm sure we can all agree on is that each has its pros and cons, its uses and not, and expain what those are correctly, hopefully without confusing energy efficiency with energy use.

PS switchbanks are not always a no-no for retrofit, the last one I put in was retrofit, the 2 lights the original single switch supplied each had a cable from the switch, so it was simply a case of replacing the switch, cost about £1. NT 22:47, 9 August 2007 (BST)

earlier response...

I attempted to both explain this while also acknowledging dimmer's use reduction in a narrow sense. If unsuccessful, clarification may be of value, but we should not throw out the key points imho. NT 08:01, 9 August 2007 (BST)

House fires

This stat about house fires: "In 2001 there were 69,000 house fires in UK" seems to occur with some regularity in the wiki. However it always seems to be followed by the cop-out "How many of these were caused <insert topic under discussion> is not known".

What is the point? It seems to be used as some form of guilt by association - i.e. I don't really approve of dimmers/flilament lamps/whatever so I will mention them alongside this stat in the hope you will pick up some negative vibe.

I feel that we could more usefully use information like this if we sweep it all into a dedicated article on house fires and their prevention, with links to the stats and the DIY related things that can be done to mitigate the risk.

For example, in 2003 one telling stat is that of the house fire deaths (approx 500) over half occurred in houses without smoke alarms, and yet nationally over 75% of domestic property has them. (interestingly over a fifth were started deliberately - perhaps one DIY aspect we could skip!)

--John Rumm 02:06, 19 August 2007 (BST)

I've been thinking for a while about a safety article that looks at the real death & injury rates of various DIY related things, to help people get a reality based idea of how much risks are present, and what is and isnt a problem. House fire data could either be its own article or a section of that one, either way.

Why are the figures included here? To give some indication of the magnitude of the risk being discussed. Its a shame the full data isnt known, but the reality that filament lighting does cause (an unknown pecentage of) fires is got across. It seems to me a relevant point. NT 12:04, 19 August 2007 (BST)

That was part of my point... "To give some indication of the magnitude of the risk being discussed" seems to be something that this stat spectacularly fails to do each time it is used. It is just so much noise. Unless you know the percentages of house fires caused by hot filament bulbs (a very low figure I would expect), then knowing the total number of household fires tells you nothing. (especially when you don't know how many households there are, and what year the figures are for). --John Rumm 00:22, 1 September 2007 (BST)

It makes the point that they do cause fires. I dont see that to be noise. NT 09:45, 1 September 2007 (BST)

We don't know that they do. So why speculate? Even if we are convinced they do, can we compare the risk to other more well known risks to establish if it is something worth worrying about?

Why don't we do an article (or two) on DIY Accidents. There are two subjects we could cover - the risks of DIY itself and how to mitigate them. Then another on the general risk we face in the home (trips, falls, burns, fires, shocks etc) and what can be done to reduce these (handrails, smoke alarms, getting shot of trailing leads etc). It would seem to be a place we could concentrate what fire stats we can find, and then link to it in other articles. Otherwise we are going to end up with rather vague warnings scattered all over the place.

Thought on titles for the articles? How about "Is your home a deathtrap?" might grab some attention. "DIY visits to Accident and Emergency". --John Rumm 14:04, 1 September 2007 (BST)

The Stanley Unwin school...

NT, most of the tweaks help, but there are couple of bits I am not as sure about...

One of your latest changes says:

"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."

Some problems with this. First, I think getting into details of triacs etc is ott for the point in hand. What is significant is the lamp on the dimmer will run very slightly below maximum voltage. This can actually make a fairly significant different to life. Most decent dimmers also include "soft start" which is also effective at increasing lamp life - especially on halogens (50 to 100% increase in lamp life some sources suggest).

Saying "Dimmers at full brightness have a slight energy efficiency disadvantage" seems to be obtuse way of saying "Dimmers on full brightness will use slightly less energy than an ordinary switch in the same circumstance". i.e. what matters is you get an absolute (although small) reduction in energy usage. Yes the efficiency in terms of lumens/watt has also gone down, but that is not useful information in the context given you can't do anything about it.

The second point is you have gone back to mixing absolute energy and energy efficiency in the same sentence "with a tiny consequent saving on bulb manufacturing energy" vs, "but this is much smaller in size than the energy efficiency reduction due to operating at slightly lower rms voltage" it is really not clear at all what you are trying to say.

I don't see any need to include "spin" in these articles to make the choice of dimmer vs switchbank even less attractive. The figures speak for themselves. At the same time, there is no need to discourage use of a dimmer if the acceptable choices for the homeowner are "keep it like it is" or "fit a dimmer" (i.e. rewiring anything to support switchbank operation does not even come onto the radar). In absolute energy consumption terms a switchbank is very good, but dimmer is still better than no dimmer if you keep the lamp powers as they were.

--John Rumm 14:42, 21 September 2007 (BST)

I dont believe all of what youre saying is entirely so, nor do I think stating the facts is spin. If there's one thing I will agree with its that the article needs work, as at least one relevant concept is no longer there. Maybe we can get into it more later, I've got to go do stuff NT 16:45, 21 September 2007 (BST)

Suggest taking this to ukdiy. But you may have an uphill path if you think reducing energy efficiency will reduce energy consumption. NT 18:50, 21 September 2007 (BST)

Energy efficiency has nothing to do with energy consumption. Energy efficiency is a ratio - not an absolute quantity.

Simple question: which uses least energy: 100W filament lamp used for 1 hour on a switch, or the same lamp used 1 hour on a dimmer?

There is no way that the dimmer can use more than the ordinary switch. We know it probably lowers the rms voltage a small amount, and hence reduces the power consumption - so the 100W bulb may now take 96W, and the switch may dissipate 1W. The overall energy consumption has fallen as well as the light output efficiency of the bulb.

I will post a summary to the group...

--John Rumm 21:47, 21 September 2007 (BST)

"There is no way that the dimmer can use more than the ordinary switch."

Then maybe a bit more subject reading would be good. NT 22:50, 21 September 2007 (BST)

For you or me? Care to explain how a series switch can cause power consumption to increase through the same bulb? Especially as it will likely cause a small voltage drop.

--John Rumm 21:03, 22 September 2007 (BST)

Plan to address the subject in the newsgroup as soon as I get enough time, so others can chip in too NT 01:45, 23 September 2007 (BST)

Reorganisation

I've reorganised the sections, combining, moving & splitting headings & content to try to make the subject clearer and less repetitive.

Some repetition has been removed, also a few tidbits that are either too trivial to warrant inclusion, mistaken or questionable, and one or 2 bits that belong better in other articles.

The paragraph about taking effect on heating system consumption into account was removed because while this is valid, imho this is something that needs to be done when recalculating the figures rather than just stated next to figures that fail to take it into account. Figures examples section needs a rework, but maybe another day.

Hopefully this lot is moving the article in the right direction. NT 08:52, 1 October 2007 (BST)

Introducing new sections made it clear another reorganisation was needed. Done, but still needs some tidying up. NT 07:39, 17 February 2012 (GMT)

I think this needs to be updated and reorganised now that various types of low energy lamps are the norm, especially dimming and LED lamps.