Difference between revisions of "Dimmers & Switchbanks"

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[[image:Dimmer 4476-3.jpg|right|250px]]
 
[[image:Dimmer 4476-3.jpg|right|250px]]
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[[image:Switchbank_new_1083-5.jpg|right|250px]]
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[[image:Switchbank_new_1083-6.jpg|right|250px]]
  
 
'''Dimmers & Switchbanks''' are both ways to control lighting levels, improving both utility and comfort.  
 
'''Dimmers & Switchbanks''' are both ways to control lighting levels, improving both utility and comfort.  
Line 7: Line 7:
  
  
−
==Advantages of Lighting Level Control==
+
=Advantages of Lighting Level Control=
 
Controllable lighting brightness permits  
 
Controllable lighting brightness permits  
 
* Relaxed lighting in the evening
 
* Relaxed lighting in the evening
 
* Bright lighting when its needed for a task
 
* Bright lighting when its needed for a task
−
* Improved safety by allowing low light levels to be used at night; particularly advantageous if small children are about.  
+
* Improved safety by allowing lighting level to be selected which is appropriate for the task in hand.  
 
* Better comfort and better visibility.
 
* Better comfort and better visibility.
−
* Can often reduce energy use, but doesn't always
+
* May reduce energy use
  
−
 
+
=Methods of Lighting Level Control=
−
==Methods of Lighting Level Control==
+
==Dimmer & dimmable lamp==
−
 
+
[[image:Dimmer 4476-3.jpg|right|190px]]
−
===Switchbank===
 
−
A '''Switchbank''' is a bank of 2 or more switches, where each switch controls some of the lights in a room. More than one lighting level is thus achieved depending on which lights are on.
 
−
 
 
−
To operate well, switchbanks require lights to have overlapping lighting areas; so a long room with only two lights, one at each end, may not be an ideal candidate for a switchbank, since turning one off would leave half the room dark and the other half bright. This can be an issue when fitting switchbanks to an installation with a minimum number of lights, as was common practice in the 1970s and before.
 
−
 
 
−
When using a switchbank with multiple downlighters, there are various ways to distribute the lights among the switches. Groups of lights on each switch and alternate lights on each switch are both popular options. What works best depends on the room and lighting layout.
 
−
 
 
−
2 or 3 switches is enough for most people. More switches make for more possible lighting patterns or levels if desired.
 
−
 
 
−
===Dimmer===
 
 
A '''Dimmer''' is an electronic control that reduces the power flowing through the lamps it controls, which in turn causes a continuously variable change in brightness to be achieved.
 
A '''Dimmer''' is an electronic control that reduces the power flowing through the lamps it controls, which in turn causes a continuously variable change in brightness to be achieved.
  
−
The reduction in brightness is not matched in proportion with a reduction in energy consumption, since a good proportion of the energy requirement for a filament lamp is just getting it hot enough to begin to glow. Measurement of a halogen lamp showed 60% rated power consumption at apx 8% light output.
+
Depending on the lamp technology, the reduced brightness may also reduce the energy consumption. Note that a [[filament lamp]] will still use a significant proportion of its "full brightness" energy, even when dimmed.  
  
 
Dimmers don't require any overlap in lighting areas to achieve their effect.
 
Dimmers don't require any overlap in lighting areas to achieve their effect.
  
−
===Combination===
+
===Compatibility===
−
A less popular option is to combine both techniques. There are a few possible ways to do this:
 
−
# Dimmer followed by switchbank
 
−
# Multiple dimmers
 
−
# A switch for some lights, and a dimmer for the other lights
 
−
 
 
−
This gives some the advantages of a switchbank while retaining the continuously variable nature of the dimmer.
 
−
 
 
−
 
 
−
==Compatibility==
 
−
===Lighting Compatibility===
 
−
====Switchbank====
 
−
Switchbanks are compatible with all types of lighting.
 
−
 
 
−
====Dimmer====
 
 
Standard dimmers have restrictions on the types of lights they will run.
 
Standard dimmers have restrictions on the types of lights they will run.
 
* Fully compatible with mains filament bulbs
 
* Fully compatible with mains filament bulbs
−
* Fully compatible with mains halogens.
+
* Fully compatible with mains [[halogen]]s.
 
* Compatible with most electronic 12V halogen lighting transformers, but not all.
 
* Compatible with most electronic 12V halogen lighting transformers, but not all.
 
* Not compatible with toroidal halogen lighting transformers.
 
* Not compatible with toroidal halogen lighting transformers.
−
* Not compatible with CFL
+
* Compatible only with [[CFL]]s specifically marked as dimmable
−
* Not compatible with linear fluorescent
+
* Compatible only with [[LED]]s specifically marked as dimmable
−
* Not compatible with discarge lighting (HID, sodium, mercury)
+
* Not compatible with linear [[fluorescent]] unless fitted with special dimmable electronic ballast and compatible dimmer switch
−
 
+
* Not compatible with [[discharge lighting]] (HID, sodium, mercury)
−
Dimmable [[Fluorescent Lighting|fluorescent lighting]] ballasts are available. When used the dimmer & ballast chosen must be compatible with each other.
 
  
−
Special dimmable CFLs are available, but are relatively high priced and little used.
+
Note that the dimming range for some dimmable LED and CFL lamps can be far narrower than for an incandescent lamp - typically the dimmest setting is quite a bit brighter than that of an incandescent lamp (this however does depend on the dimmer - ones specifically designed for LED use for example tend to achieve far better results.  
  
−
===Wiring Compatibility===
+
Also note that unlike an incandescent lamp the colour temperature of LED and CLF lamps does not get significantly lower as they dim - so they can seem somewhat "cold" looking when dimmed.
−
====Dimmer====
 
−
Dimmers can easily replace a single lightswitch in an existing installation, with no need for any extra wiring to be installed. This makes them an easy option for existing installations.
 
  
−
====Switchbank====
+
===Reliability===
−
Switchbanks can sometimes be retrofitted with no change in wiring, but in the majority of cases this is not possible, and extra [[Cables|cable]] would need to be run to enable them to be retrofitted. This heavily limits their retrofit use.
+
Dimmers themselves aren't as reliable as switches, and failures do occur occasionally. 250w dimmers are rather less robust on the whole than 500w dimmers.  
  
−
 
+
Filament bulbs occasionally consume a heavy current surge on failure, due to arc-over. Such a current surge has a high chance of destroying a dimmer. These surges are more likely to occur with
−
==The Lightbulb Ban==
 
−
The proposed ban of filament lightbulbs failed to happen, so dimmer users shouldn't have any difficulty getting the usual lamp types.
 
−
 
 
−
==Reliability==
 
−
===Switchbanks===
 
−
Switchbanks are as reliable as any other light switch arrangement, ie very reliable.
 
−
 
 
−
If more lights are fitted at the same time, that translates to more lightbulb replacements. This is not generally a cost disadvantage due to greater running energy efficiency than dimmed lamps, but can be if installation costs are high.
 
−
 
 
−
A switchbank also provides component redundancy, meaning that if any one element fails, the system as a whole still continues to work.
 
−
 
 
−
===Dimmers===
 
−
Dimmers have lower and more variable reliability compared to switches, and failures do occur occasionally. 250w dimmers are rather less robust on the whole than 500w dimmers. A dimmer is also a single failure point, meaning a failure can cause whole room lighting failure.
 
−
 
 
−
Filament bulbs occasionally consume a heavy current surge on failure, due to arc-over. Such a current surge has a high chance of destroying a dimmer. These surges are more likely to occur and be of higher currents with
 
 
* small form factor mains filament bulbs (especially [[Halogen Lighting|mains halogen]])
 
* small form factor mains filament bulbs (especially [[Halogen Lighting|mains halogen]])
 
* short [[Cables|cable]] runs.
 
* short [[Cables|cable]] runs.
 +
 +
Some dimmers include "soft start" facilities. These may enhance the life span of halogen lamps in particular.
  
 
12v bulbs and non-filament type lamps don't suffer from this.
 
12v bulbs and non-filament type lamps don't suffer from this.
  
−
Specifying a 500w dimmer with well below 500w of lighting load can improve reliability, although it does not solve the above minor issues.
+
Dimmers should not be loaded past their max rating, this elevates failure rate greatly. Note also that many dimmers also have a minimum load required for correct operation - this can be a problem with some LED loads due to their low current draw.  
  
−
Dimmers should not be loaded past their max rating, as this will elevate failure rate greatly.
+
===Wiring Arrangements===
 +
A dimmer usually replaces an existing switch, with no added complication. (although note that remote control dimmer switches may not work with low energy lamps unless a bleed resistor is also fitted to allow a small current to flow through the lamp when "off")
  
 +
The exception to this is when [[2 Way Switching|two way]] operation is required. If you wish to control brightness from both switch positions then a special master / slave dimmer switch will be required. Conventional dimmers will allow [[2 Way Switching|two way switching]], but not two way brightness control.
  
−
==Bulb Life==
+
==Switchbank==
−
Switchbanks have no effect on lamp life.
+
[[image:Switchbank_new_1083-6.jpg|right|190px]][[image:GEC-grid-1.jpg|right|180px]][[image:GEC-grid-2.jpg|right|180px]][[image:GEC-grid-3.jpg|right|180px]] [[image:MK-grid-1.jpg|right|180px]] [[image:MK-Grid-2.jpg|right|180px]]
  
−
Dimmers usually soft start lamps. This extends mains halogen lamp life to some extent, but makes insignificant difference with all other types of lamp.
 
  
 +
A '''Switchbank''' is a bank of 2 or more switches, where each switch controls some of the lights in a room. More than one [[lighting]] level is thus achieved depending on the number and combination of lights turned on.
  
−
==Installation Costs==
+
To operate well, switchbanks require lights to have overlapping lighting areas; so a long room with only two lights, one at each end, may not be an ideal candidate for a switchbank. Uneven lighting can be an issue when fitting switchbanks to an installation with a minimum number of lights, as was common practice in the 1970s and before.
  
−
===Switchbanks===
+
When using a switchbank with multiple downlighters, there are various ways to distribute the lights among the switches. Groups of lights on each switch and alternate lights on each switch are both popular options. What works best depends on the room and lighting layout.
−
Fitting a switch bank requires more materials (a multi-gang switch & [[Cables|cable]]), and a little extra labour than a dimmer. The extra cost of [[Special:Allpages|DIY]] fitting is usually paid back many times over in the life of the installation by reduced electricity use.  
 
  
−
This is not the case with retrofits where channelling and plastering is required to make good.
+
2 or 3 switches are often enough for most rooms. More switches make for more possible lighting patterns or levels if desired.
  
−
A switchbank can also be used to mix or choose between filament lighting and [[CFL Lamps|CFL]]. For example, someone that is not keen on [[CFL Lamps|CFL]] might use filament, and their partner [[CFL Lamps|CFL]], or they might use a mixture of lighting types. One example of this would be concealed [[Fluorescent Lighting|fluorescent uplighting]] with [[Halogen Lighting|halogen]] spots for task and feature lighting.
+
===Compatibility===
 +
Switchbanks are compatible with all types of [[lighting]].
  
−
===Dimmers===
+
===Reliability===
−
Fitting a dimmer is normally a simple low cost job.
+
Switchbanks are as reliable as any other light switch arrangement. If more lights are fitted at the same time, that translates to more routine bulb replacements.  
  
 +
===Installation Tips===
 +
Single sized standard light switches come with up to 4 switches, plenty for most rooms.
  
−
==Installation Tips==
+
====More Switches====
  
−
===Switching for Switchbanks===
+
Large and specialist lighting installs may require more switches. Standard double faceplates come with upto 6 switches. To get even more switches requires either a '''gridswitch''', additional faceplates, or a custom switch assembly made from a blanking plate. The '''gridswitch''' is the usual choice, and can incorporate dimmers and indicators etc as well as switches.
−
With standard faceplates, a single sized light switch can come with up to 3 switches. A 3 gang switch is plenty for most rooms.
 
  
−
====More Switches====
+
Each additional switch doubles the number of available lighting patterns, hence 3 and 4 gang switchbanks are normally plenty.  
−
Grand buildings, public halls and specialist lighting installations may require more switches. Standard double faceplates come with upto 6 switches. To get even more switches requires either a gridswitch, additional faceplates, or a custom switch assembly made from a blanking plate. The gridswitch is the usual choice.
+
* A 2 gang switch gives 3 lighting levels, if the lights are of different wattage
−
 
 
−
Each additional switch and set of controlled lights will double the number of available lighting patterns, hence 3 and 4 gang switchbanks are normally plenty.  
 
−
* A 2 gang switch gives 3 lighting levels
 
 
* A 3 gang switch gives 7 lighting patterns/levels
 
* A 3 gang switch gives 7 lighting patterns/levels
 
* A 4 gang switch gives 15 lighting combinations & levels!
 
* A 4 gang switch gives 15 lighting combinations & levels!
  
−
Dimmers can also be incorporated into gridswitches.
+
Shown at right, an 8-gang GEC metalclad gridswitch with 8 intermediate switches. This would have 32 strapping wires connected to the switches, plus CPCs and any neutrals passing through the box.
  
−
 
+
===Wiring Arrangements===
−
==Wiring Arrangements==
 
−
===Dimmers===
 
−
A dimmer usually replaces an existing switch, with no added complication.
 
−
 
 
−
The exception to this is when [[2_Way_Switching|two way]] operation is required. If you wish to control brightness from both switch positions then a special master / slave dimmer switch will be required. Conventional dimmers will allow [[2 Way Switching|two way switching]], but not two way brightness control.
 
−
 
 
−
===Switchbanks===
 
 
====Loop-in====
 
====Loop-in====
−
The majority of [[House Wiring for Beginners|domestic lighting circuits]] are wired using the [[House Wiring for Beginners|"loop in"]] method. Here power is daisy-chained from each lighting fitting to the next, and a separate switch wire connects a switch to each fitting. This is a simple and easy to implement system for [[House Wiring for Beginners|general lighting wiring]], but is not compatible as it stands with switchbanks. To retrofit switchbanks into such a system would require additional wiring, complicating the wiring layout.
+
[[House Wiring for Beginners|Loop-in]] is the most common lighting circuit arrangement. Power is daisy-chained from each lighting fitting to the next, and a separate switch wire connects a switch to each fitting. This is simple and easy to implement for [[House Wiring for Beginners|general lighting wiring]], but is not compatible as it stands with switchbanks. To retrofit switchbanks into such a system would require additional wiring, complicating the wiring layout.
  
−
====name here====
+
====Switch loop through====
 
The other method in use for domestic lighting is to run the power feed to the switch first rather than the lighting (so power feed to the next room is taken from the switch position and not from a light fitting). From the switch, a [[Cables|cable]] with neutral, earth & switched live is run to the lighting. A minority of house lighting is wired this way.
 
The other method in use for domestic lighting is to run the power feed to the switch first rather than the lighting (so power feed to the next room is taken from the switch position and not from a light fitting). From the switch, a [[Cables|cable]] with neutral, earth & switched live is run to the lighting. A minority of house lighting is wired this way.
  
 
When more than one [[Cables|cable]] is run from the light switch to more than one light fitting, a switchbank can be retrofitted without adding any further wiring. However in most retrofit cases such wiring is not already present. Hence switchbanks are more often fitted at new installation and [[Rewiring Tips|rewire times]] rather than retrofitted.
 
When more than one [[Cables|cable]] is run from the light switch to more than one light fitting, a switchbank can be retrofitted without adding any further wiring. However in most retrofit cases such wiring is not already present. Hence switchbanks are more often fitted at new installation and [[Rewiring Tips|rewire times]] rather than retrofitted.
  
−
====One only====
+
==Combined dimmer & switchbank==
−
Occasionally its wanted to provide just one power feed at a time, and not both or all. This may be done when 2 or more lightbulbs are going in one light fitting, and:
+
Another option is to combine both techniques. There are a few possible ways to do this:
−
* operating both at the same time would take the fitting over its rated power,
+
# Dimmer followed by switchbank
−
* or would operate filament and cfl bulbs at the same time, causing overheating of the CFL
+
# Multiple dimmers
 +
# A switch for some lights, and a dimmer for the other lights
  
−
In these cases, a set of switches can be wired to provide power to only one output. Note that this 1-only setup can equally well cover either all switches in a switchbank, or just some, as needed.
+
This gives some the advantages of a switchbank while retaining the continuously variable nature of the dimmer.
  
−
                          o
 
−
              o---------O--
 
−
Live -----O--            o
 
−
              o            |
 
−
              |            |
 
−
              |    switched live 2
 
−
      switched live 1
 
  
−
Ideally switched live 1 should supply the most often wanted lighting feed, as with live feed 1 on, switch 2 won't turn live feed 2 on.
+
==Switch dimmable low energy lamps==
 +
Lamps are available that will select more than one brightness level, controlled by operating an ordinary lightswitch a number of times in sequence. These allow dimming with no wiring changes.
  
−
==Energy Efficiency & Running Cost==
+
===Compatibility===
−
===Dimmers===
+
As only the bulb is changed to get this feature, the fitting remains compatible with all lighting types. These are not usually compatible with conventional dimmer switches.
−
While it is often assumed that fitting a dimmer will reduce energy use, the reality is more complex. In some cases energy is saved, and in some cases energy use increases. See [http://groups.google.co.uk/group/uk.d-i-y/browse_frm/thread/367443d4f036010c/d1d1bf8a115532fb?hl=en&lnk=gst&q=illumination+needed&rnum=3#d1d1bf8a115532fb this discussion] for explanation and detail.
 
  
−
For users who frequently use less than maximum brightness illumination, the energy saving potential of a switchbank is much greater.
+
==Home automation dimmers==
 +
Dimmer systems are available for integration with home automation systems. These are typically controlled by either proprietary RF signalling, or more commonly, by WiFi. These allow brightness (ans in some cases colour) to be controlled from an "App" on a smart phone or tablet. With home automation systems wither the lamp socket itself can be "smart" or you can opt for "smart" bulbs.  
  
−
For users who rarely use less than maximum brightness illumination, neither option could save significant energy or cost.
 
  
 +
==Boost & dim==
 +
An 18v transformer can be used to provide 3 settings of boost, normal and dim for filament lamps. The result is significantly better energy efficiency that just a dimmer. The transformer is wired to give 222v, 240v or 258v.
  
−
===Switchbanks===
+
Its also possible to implement 2 brightness settings by using a bridge rectifier and capacitor, to give normal and boosted rms voltage.
−
All lighting on a switchbank runs at full energy efficiency, hence switchbanks are an inherently more energy efficient option than dimmers.  
 
  
−
Switchbanks are also compatible with all lighting types, whereas dimmers only work with the higher energy consumption types of lighting (tungsten filament & [[Halogen Lighting|halogen]]). Energy efficiency and compatibility are the main advantages of switchbank over dimmer.
+
Full discussion: [[Filament_lamp#Bulb_Boosting|Bulb Boosting]] & [[Filament_lamp#Switchable_Boost|Switchable Boost]]
  
 +
===Compatibility===
 +
Compatibility depends on the method chosen. See [[Filament_lamp#Compatibility|Compatibility]]
  
−
<!-- here downward has yet to be reworked -->
 
  
 +
==Dimmable fluorescent==
 +
A dimmable fluorescent ballast enables dimming fluorescent tubes over a wide range. A dimmer control compatible with the ballast must be used.
  
−
===Examples===
+
How to make a fluorescent fitting [[Fluorescent Lighting#Fitting Types & Installation Methods|unseen]]
−
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.
+
How to ensure good [[Fluorescent Lighting#The Many Different Whites|light quality]]
  
−
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:
+
=Fitting=
−
* 1 hour a day of 40w filament equivalent output
+
==Dimmer==
−
* 5 hours a day of 150w filament equivalent output
+
Dimmers just replace a lightswitch in an existing installation, with no need for any extra wiring to be installed. Retrofitting is easy, and the cost minimal.
−
* 1 hour a day of 300w filament equivalent output (i.e. full brightness)
 
  
−
Prices are given for 10p/unit electricity cost.
+
==Switchbank==
 +
If 2 or more light fittings have their own [[cable]]s running to the switch, then a switchbank can be fitted very easily. Its just a case of replacing the old switch.
  
−
====No Control====
+
But more often there are no separate cables, and extra [[Cables|cable]] needs to be run to retrofit a switchbank. This heavily limits their retrofit use in practice.
−
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.
+
Retrofit cost is trivial in the first case, but requires additional new cable(s) in the 2nd case.  
  
−
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.  
+
The extra cost of fitting a switchbank when building new is trivial.  
  
−
If we opted for 50w of CFL instead:
+
A switchbank can also be used to mix or choose between filament and other lighting. One example of this would be concealed [[Fluorescent Lighting|fluorescent uplighting]] with [[Halogen Lighting|halogen]] spots for task and feature lighting.
  
−
7 hours at 50W = 0.35kWh / day = £13 pa = £319 per 25 yr installation life.
 
  
−
====Switchbank====
+
=Bulb Life=
−
A total of 300W of filament lamps on switchbank will use:
+
Switchbanks have no effect on lamp life.
−
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:
+
Dimmers usually soft start lamps. This extends mains [[halogen]] lamp life to some extent, but may make less difference with all other types of lamp.  
−
0.015 + 5 x 0.8 + 0.1 kWh = 0.195kWh / day = £7 / year = £177 per 25 yr installation life.
 
  
−
====Dimmer====
+
Switch dimmed [[cfls]] and dimmed linear [[fluorescent]] tubes last far longer than filament lamps. Dimming them has little effect on lamp life. Linear fluorescent tubes on electronic ballasts see around 20,000 hour life average.
−
For 300w of [[Halogen Lighting|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
+
Boost dimming reduces filament lamp life when on max setting.
  
−
===Energy Efficiency Summary===
 
  
−
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"
+
=Energy Efficiency & Running Cost=
−
|-
+
While it is often assumed that fitting a dimmer will reduce energy use, the reality may be more complex. If you elect to use a more powerful filament lamp than you otherwise would have, running costs may actually increase.
−
!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
 
−
|-
 
−
 
−
|}
 
  
−
From this comparison table several things can be seen:
+
If frequently using less than maximum brightness illumination, the energy saving potential of a switchbank is much greater.
−
# 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.
 
−
# 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.
 
−
# 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.
 
  
 +
For users who normally always run their lamps at maximum brightness illumination, neither option will save significant energy or cost.
  
  
−
==Summary==
+
=Summary=
−
* Switchbanks are a good idea for new installs, and if used in the intended way, may save many times their cost.
+
* Switchbanks are a good idea for new installs.
−
* Dimmers won't save as much money as a switch bank, and if lamp powers are not carefully chosen may end up costing more than a non controlled lighting system.
 
 
* Dimmers are the neat option for multi-bulb chandeliers.
 
* Dimmers are the neat option for multi-bulb chandeliers.
 
* Dimmers are significantly easier and thus cheaper to retrofit than switchbanks.
 
* Dimmers are significantly easier and thus cheaper to retrofit than switchbanks.
 
* Dimmers give the greatest amount of lighting level control
 
* Dimmers give the greatest amount of lighting level control
−
* Dimmers prevent use of [[CFL Lamps]].
 
−
 
−
 
  
−
==See Also==
 
−
[[Special:Allpages|Wiki Contents]]
 
  
−
[[Special:Categories|Wiki Subject Categories]]
+
=See Also=
 +
* [[Special:Allpages|Wiki Contents]]
 +
* [[Special:Categories|Wiki Subject Categories]]
  
  

Revision as of 09:55, 12 July 2019

Dimmer 4476-3.jpg
Switchbank new 1083-6.jpg

Dimmers & Switchbanks are both ways to control lighting levels, improving both utility and comfort.

This article sets out the advantages of controlled lighting levels, and looks at the relative merits of different ways of achieving them. Some installation notes are also included.


Advantages of Lighting Level Control

Controllable lighting brightness permits

  • Relaxed lighting in the evening
  • Bright lighting when its needed for a task
  • Improved safety by allowing lighting level to be selected which is appropriate for the task in hand.
  • Better comfort and better visibility.
  • May reduce energy use

Methods of Lighting Level Control

Dimmer & dimmable lamp

Dimmer 4476-3.jpg

A Dimmer is an electronic control that reduces the power flowing through the lamps it controls, which in turn causes a continuously variable change in brightness to be achieved.

Depending on the lamp technology, the reduced brightness may also reduce the energy consumption. Note that a filament lamp will still use a significant proportion of its "full brightness" energy, even when dimmed.

Dimmers don't require any overlap in lighting areas to achieve their effect.

Compatibility

Standard dimmers have restrictions on the types of lights they will run.

  • Fully compatible with mains filament bulbs
  • Fully compatible with mains halogens.
  • Compatible with most electronic 12V halogen lighting transformers, but not all.
  • Not compatible with toroidal halogen lighting transformers.
  • Compatible only with CFLs specifically marked as dimmable
  • Compatible only with LEDs specifically marked as dimmable
  • Not compatible with linear fluorescent unless fitted with special dimmable electronic ballast and compatible dimmer switch
  • Not compatible with discharge lighting (HID, sodium, mercury)

Note that the dimming range for some dimmable LED and CFL lamps can be far narrower than for an incandescent lamp - typically the dimmest setting is quite a bit brighter than that of an incandescent lamp (this however does depend on the dimmer - ones specifically designed for LED use for example tend to achieve far better results.

Also note that unlike an incandescent lamp the colour temperature of LED and CLF lamps does not get significantly lower as they dim - so they can seem somewhat "cold" looking when dimmed.

Reliability

Dimmers themselves aren't as reliable as switches, and failures do occur occasionally. 250w dimmers are rather less robust on the whole than 500w dimmers.

Filament bulbs occasionally consume a heavy current surge on failure, due to arc-over. Such a current surge has a high chance of destroying a dimmer. These surges are more likely to occur with

Some dimmers include "soft start" facilities. These may enhance the life span of halogen lamps in particular.

12v bulbs and non-filament type lamps don't suffer from this.

Dimmers should not be loaded past their max rating, this elevates failure rate greatly. Note also that many dimmers also have a minimum load required for correct operation - this can be a problem with some LED loads due to their low current draw.

Wiring Arrangements

A dimmer usually replaces an existing switch, with no added complication. (although note that remote control dimmer switches may not work with low energy lamps unless a bleed resistor is also fitted to allow a small current to flow through the lamp when "off")

The exception to this is when two way operation is required. If you wish to control brightness from both switch positions then a special master / slave dimmer switch will be required. Conventional dimmers will allow two way switching, but not two way brightness control.

Switchbank

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A Switchbank is a bank of 2 or more switches, where each switch controls some of the lights in a room. More than one lighting level is thus achieved depending on the number and combination of lights turned on.

To operate well, switchbanks require lights to have overlapping lighting areas; so a long room with only two lights, one at each end, may not be an ideal candidate for a switchbank. Uneven lighting can be an issue when fitting switchbanks to an installation with a minimum number of lights, as was common practice in the 1970s and before.

When using a switchbank with multiple downlighters, there are various ways to distribute the lights among the switches. Groups of lights on each switch and alternate lights on each switch are both popular options. What works best depends on the room and lighting layout.

2 or 3 switches are often enough for most rooms. More switches make for more possible lighting patterns or levels if desired.

Compatibility

Switchbanks are compatible with all types of lighting.

Reliability

Switchbanks are as reliable as any other light switch arrangement. If more lights are fitted at the same time, that translates to more routine bulb replacements.

Installation Tips

Single sized standard light switches come with up to 4 switches, plenty for most rooms.

More Switches

Large and specialist lighting installs may require more switches. Standard double faceplates come with upto 6 switches. To get even more switches requires either a gridswitch, additional faceplates, or a custom switch assembly made from a blanking plate. The gridswitch is the usual choice, and can incorporate dimmers and indicators etc as well as switches.

Each additional switch doubles the number of available lighting patterns, hence 3 and 4 gang switchbanks are normally plenty.

  • A 2 gang switch gives 3 lighting levels, if the lights are of different wattage
  • A 3 gang switch gives 7 lighting patterns/levels
  • A 4 gang switch gives 15 lighting combinations & levels!

Shown at right, an 8-gang GEC metalclad gridswitch with 8 intermediate switches. This would have 32 strapping wires connected to the switches, plus CPCs and any neutrals passing through the box.

Wiring Arrangements

Loop-in

Loop-in is the most common lighting circuit arrangement. Power is daisy-chained from each lighting fitting to the next, and a separate switch wire connects a switch to each fitting. This is simple and easy to implement for general lighting wiring, but is not compatible as it stands with switchbanks. To retrofit switchbanks into such a system would require additional wiring, complicating the wiring layout.

Switch loop through

The other method in use for domestic lighting is to run the power feed to the switch first rather than the lighting (so power feed to the next room is taken from the switch position and not from a light fitting). From the switch, a cable with neutral, earth & switched live is run to the lighting. A minority of house lighting is wired this way.

When more than one cable is run from the light switch to more than one light fitting, a switchbank can be retrofitted without adding any further wiring. However in most retrofit cases such wiring is not already present. Hence switchbanks are more often fitted at new installation and rewire times rather than retrofitted.

Combined dimmer & switchbank

Another option is to combine both techniques. There are a few possible ways to do this:

  1. Dimmer followed by switchbank
  2. Multiple dimmers
  3. A switch for some lights, and a dimmer for the other lights

This gives some the advantages of a switchbank while retaining the continuously variable nature of the dimmer.


Switch dimmable low energy lamps

Lamps are available that will select more than one brightness level, controlled by operating an ordinary lightswitch a number of times in sequence. These allow dimming with no wiring changes.

Compatibility

As only the bulb is changed to get this feature, the fitting remains compatible with all lighting types. These are not usually compatible with conventional dimmer switches.

Home automation dimmers

Dimmer systems are available for integration with home automation systems. These are typically controlled by either proprietary RF signalling, or more commonly, by WiFi. These allow brightness (ans in some cases colour) to be controlled from an "App" on a smart phone or tablet. With home automation systems wither the lamp socket itself can be "smart" or you can opt for "smart" bulbs.


Boost & dim

An 18v transformer can be used to provide 3 settings of boost, normal and dim for filament lamps. The result is significantly better energy efficiency that just a dimmer. The transformer is wired to give 222v, 240v or 258v.

Its also possible to implement 2 brightness settings by using a bridge rectifier and capacitor, to give normal and boosted rms voltage.

Full discussion: Bulb Boosting & Switchable Boost

Compatibility

Compatibility depends on the method chosen. See Compatibility


Dimmable fluorescent

A dimmable fluorescent ballast enables dimming fluorescent tubes over a wide range. A dimmer control compatible with the ballast must be used.

How to make a fluorescent fitting unseen How to ensure good light quality

Fitting

Dimmer

Dimmers just replace a lightswitch in an existing installation, with no need for any extra wiring to be installed. Retrofitting is easy, and the cost minimal.

Switchbank

If 2 or more light fittings have their own cables running to the switch, then a switchbank can be fitted very easily. Its just a case of replacing the old switch.

But more often there are no separate cables, and extra cable needs to be run to retrofit a switchbank. This heavily limits their retrofit use in practice.

Retrofit cost is trivial in the first case, but requires additional new cable(s) in the 2nd case.

The extra cost of fitting a switchbank when building new is trivial.

A switchbank can also be used to mix or choose between filament and other lighting. One example of this would be concealed fluorescent uplighting with halogen spots for task and feature lighting.


Bulb Life

Switchbanks have no effect on lamp life.

Dimmers usually soft start lamps. This extends mains halogen lamp life to some extent, but may make less difference with all other types of lamp.

Switch dimmed cfls and dimmed linear fluorescent tubes last far longer than filament lamps. Dimming them has little effect on lamp life. Linear fluorescent tubes on electronic ballasts see around 20,000 hour life average.

Boost dimming reduces filament lamp life when on max setting.


Energy Efficiency & Running Cost

While it is often assumed that fitting a dimmer will reduce energy use, the reality may be more complex. If you elect to use a more powerful filament lamp than you otherwise would have, running costs may actually increase.

If frequently using less than maximum brightness illumination, the energy saving potential of a switchbank is much greater.

For users who normally always run their lamps at maximum brightness illumination, neither option will save significant energy or cost.


Summary

  • Switchbanks are a good idea for new installs.
  • Dimmers are the neat option for multi-bulb chandeliers.
  • Dimmers are significantly easier and thus cheaper to retrofit than switchbanks.
  • Dimmers give the greatest amount of lighting level control


See Also

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