Difference between revisions of "Dimmers & Switchbanks"

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'''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.
+
[[image:Dimmer 4476-3.jpg|right|250px]]
 +
[[image:Switchbank_new_1083-6.jpg|right|250px]]
  
 +
'''Dimmers & Switchbanks''' are both ways to control lighting levels, improving both utility and comfort.
  
−
==Advantages of Lighting Level Control==
+
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  
 
Controllable lighting brightness permits  
 +
* Relaxed lighting in the evening
 
* Bright lighting when its needed for a task
 
* Bright lighting when its needed for a task
−
* Relaxed lighting in the evening
+
* Improved safety by allowing lighting level to be selected which is appropriate for the task in hand.  
−
* Improved safety by allowing low light levels to be used at night; particularly advantageous if small children are about.  
+
* Better comfort and better visibility.
−
* Give better comfort and better visibility.
+
* May reduce energy use
−
* Can reduce energy usage
+
 
 +
=Methods of Lighting Level Control=
 +
==Dimmer & dimmable lamp==
 +
[[image:Dimmer 4476-3.jpg|right|190px]]
 +
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 [[halogen]]s.
 +
* Compatible with most electronic 12V halogen lighting transformers, but not all.
 +
* Not compatible with toroidal halogen lighting transformers.
 +
* Compatible only with [[CFL]]s specifically marked as dimmable
 +
* Compatible only with [[LED]]s 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.
  
−
How it affects [[Save Energy & Money|energy use and running costs]] will depend on which method of control is used, and the pattern of use.  
+
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
 +
* small form factor mains filament bulbs (especially [[Halogen Lighting|mains halogen]])
 +
* short [[Cables|cable]] runs.
  
−
==Methods of Lighting Level Control==
+
Some dimmers include "soft start" facilities. These may enhance the life span of halogen lamps in particular.
  
−
===Switchbank===
+
12v bulbs and non-filament type lamps don't suffer from this.
−
A '''Switchbank''' is a bank of 2 or more switches, where each switch controls a subset of the total number of lights in a room. Lighting levels can be controlled in a number of discrete steps by selecting which lights are turned on.  
 
  
−
To operate well, switchbanks require lights to have overlapping lighting areas; so a long room with only two lights - one lighting 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. A room with 10 smaller downlights however could have control of the lights interleaved such that lights 1 3 5 7 & 9 are one one switch and 2 4 6 8 & 10 are on a second. This would be a far more satisfactory arrangement for a switchbank.  
+
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.  
  
−
The more switches used (and hence separately controllable lamps), the finer the control possible.
+
===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")
  
−
===Dimmer===
+
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.
−
A '''Dimmer''' is an electronic switch that reduces the power flowing through the lamps it controls, which in turn causes a continuously variable change in brightness to be achieved. Note however that 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. As a rough estimate you can say that a 90% reduction in light output may only represent a 50% reduction in power.  
 
  
−
Unlike switchbanks dimmers don't require overlapping lighting areas to archive their effect.
+
==Switchbank==
 +
[[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]]
  
−
===Combination===
 
−
It is also possible for both techniques to be combined. Here each or some of the multiple switches of a switch bank are implemented with dimmer switches. This allows all the advantages of a switchbank, while retaining the continuously variable nature of the dimmer. A potential downside to watch however is that one does actually use the switching capability in addition to the dimming one, otherwise you will not reap the full cost savings.
 
  
−
==Patterns of use==
+
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.
−
Different people use controllable lighting in different ways. Some will tend to use their lighting at or near to its maximum level most of the time, and then wish to use lower levels occasionally. Many people retrofitting dimmer switches to existing installations will fall into this category.  
 
  
−
Some will want to do the reverse, using lower lighting levels everyday, but having the option of having more (or less) brightness on occasion.  
+
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.
  
−
==Comparison of Energy Efficiency==
+
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.
−
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 (hand 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.  
+
2 or 3 switches are often enough for most rooms. More switches make for more possible lighting patterns or levels if desired.
  
−
This section compares the energy usage requirements for a hypothetical room that is equipped with 300W of filament lighting or the approximate equivalent of 100W of CFL lighting. We will assume the usage pattern in a typical day would be:
+
===Compatibility===
 +
Switchbanks are compatible with all types of [[lighting]].
  
−
1 hour a day of 40w filament equivalent output
+
===Reliability===
−
5 hours a day of 150w filament equivalent output
+
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.  
−
1 hour a day of 300w filament equivalent output (i.e. full brightness)
 
  
−
Prices are given for 10p/unit electricity cost.
+
===Installation Tips===
 +
Single sized standard light switches come with up to 4 switches, plenty for most rooms.
  
−
===No Control===
+
====More Switches====
−
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.
+
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.
  
−
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.
+
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!
  
−
If we opted for 50w of CFL instead:
+
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.
  
−
7 hours at 50W = 0.35kWh / day = £13 pa = £319 per 25 yr installation life.
+
===Wiring Arrangements===
 +
====Loop-in====
 +
[[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.
  
−
===Switchbank===
+
====Switch loop through====
−
A total of 300W of filament lamps on switchbank will use:
+
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.
−
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.
+
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.
  
−
[[CFL Lamps]] on switchbank will use:
+
==Combined dimmer & switchbank==
−
0.015 + 5 x 0.8 + 0.1 kWh = 0.195kWh / day = £7 / year = £177 per 25 yr installation life.
+
Another 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
  
−
===Dimmer===
+
This gives some the advantages of a switchbank while retaining the continuously variable nature of the dimmer.
−
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
 
  
−
===Summary===
+
==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.
  
−
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"
+
===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.
−
!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:
+
==Home automation dimmers==
−
# 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.
+
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.  
−
# 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.
 
  
−
===Reliability===
 
−
Switchbanks are typically as reliable as any other light switching arrangement (i.e. very), however the need for a larger number of independently controlled lamps will reduce the overall reliability figure a little, since there will typically be more lamps to fail and replace.
 
  
−
From a light availability point of view however a switchbank provides redundancy, meaning that if one element fails, the system as a whole still continues to work.
+
==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.
  
−
A dimmer is a single failure point, and dimmers have variable reliability. The cheaper 250w dimmers seem on the whole to be less robust in this respect. It is generally better to specify a dimmer with greater power handling than you actually require by a reasonable margin (say 50%). A dimmer can operate with a single lamp or cluster of lamps and will hence tend to improve lamp reliability. Many also include a soft start capability that is beneficial in extending halogen lamp life in particular.  
+
Its also possible to implement 2 brightness settings by using a bridge rectifier and capacitor, to give normal and boosted rms voltage.
  
−
Dimmers are rated for their maximum power ratings (and in the case of ones used with LV lamps often a minimum load as well). If dimmers are used over their ratings, early failure is likely.
+
Full discussion: [[Filament_lamp#Bulb_Boosting|Bulb Boosting]] & [[Filament_lamp#Switchable_Boost|Switchable Boost]]
  
 
===Compatibility===
 
===Compatibility===
−
Standard dimmers are compatible with mains filament bulbs & mains halogens. They are also generally compatible with 12V lighting systems, but a little care mut be taken to pair the correct type of dimmer and transformer or power supply.  
+
Compatibility depends on the method chosen. See [[Filament_lamp#Compatibility|Compatibility]]
  
−
Dimmable [[Fluorescent Lighting|fluorescent lighting]] ballasts are available. Dimming these does reduce the energy efficiency of fluorescent lamps to some extent, but nowhere near as much as with filament lamps.
 
  
−
CFLs and dimmers are generally not compatible (special dimmable CFLs are available in some countries, but generally not the UK).
+
==Dimmable fluorescent==
 +
A dimmable fluorescent ballast enables dimming fluorescent tubes over a wide range. A dimmer control compatible with the ballast must be used.
  
−
Dimmers have a significant compatibility advantage, which is that they can easily replace a single lightswitch in an existing installation, with no need for any extra wires to be put in. However, depending on how much power and time dimmed lighting is used, retrofitting a switchbank and adding any extra wire needed can work out cheaper, as well as being more energy efficient.
+
How to make a fluorescent fitting [[Fluorescent Lighting#Fitting Types & Installation Methods|unseen]]
 +
How to ensure good [[Fluorescent Lighting#The Many Different Whites|light quality]]
  
−
===Run and installation Costs===
+
=Fitting=
−
Run cost depends entirely on what lighting is used at what setting for how long, so is a very variable figure. One must also allow for the fact that the heat produced from the lighting will contribute to the heat released into the building. In the winter this may be desirable to an extent and will partially offset heating costs (although using more expensive electric heating in place of cheaper gas or oil). In summer this is counter productive, especially if you have to pay for air-conditioning to vent the unwanted heat.  
+
==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.
  
−
Fitting a switch bank obviously requires more materials (switches, cable, & luminaries), and may also require significant extra installation time and cost. However this extra install cost can be paid back many times over in the life of the installation.
+
==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.
  
−
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 might use CFL just for background light, with filament as the main lighting, or use linear fluorescent uplighting with halogen spots for task and feature lighting.
+
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.
  
−
Fitting a Dimmer is usually a simple and low cost option, however the energy saving payback is far less dramatic.  
+
Retrofit cost is trivial in the first case, but requires additional new cable(s) in the 2nd case.  
  
−
==Installation Tips==
+
The extra cost of fitting a switchbank when building new is trivial.
  
−
===Switching for Switchbanks===
+
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.
−
With standard faceplates, a single light switch can come with up to 3 typically. Standard double faceplates come with upto 6 switches. a 3 gang switch is enough for most rooms.
 
  
−
====More Switches====
 
−
More switches are not normally used outside of grand buildings and public halls. To get more switches would requires either a gridswitch, additional faceplates, or a custom switch assembly made from a blanking plate. The gridswitch is the usual choice.
 
  
−
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.
+
=Bulb Life=
 +
Switchbanks have no effect on lamp life.
  
−
If you ignore "off" as a brightness level, we are left with:
+
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.
  
−
{| border="1" cellpadding="6" cellspacing="0" style="text-align:center"
+
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.
−
|-
 
−
!Number of switches
 
−
!Patterns available
 
−
|-
 
−
| 2 || 3
 
−
|-
 
−
| 3 || 7
 
−
|-
 
−
| 4 || 15
 
−
|-
 
−
| 5 || 31
 
−
|-
 
−
| 6 || 63
 
−
|-
 
−
 
−
|}
 
  
−
It is also possible to incorporate dimmers into gridswitches.
+
Boost dimming reduces filament lamp life when on max setting.
  
−
===Wiring for switchbanks===
 
−
Most domestic lighting circuits are wired using the "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 general lighting wiring, however it may become a bit cumbersome for switchbanks with many controllable ways since you will end up with a birds nest of wiring in the ceiling void.
 
  
−
One way to reduce this complexity is to take the power feed (complete with its associated neutral) to the switch position rather than lighting position - so power out to the next room is hence taken from here and not a light fitting. From here a single cable with neutral and switched live can be run to each lighting position (or group of positions). This does away will all of the daisy chain wiring between each lighting position, and just requires a single wire out to each lighting position.
+
=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.
  
−
===Wiring for Dimmers===
+
If frequently using less than maximum brightness illumination, the energy saving potential of a switchbank is much greater.
−
A dimmer will usually simply replace and existing switch, and requires no special wiring consideration.  
 
  
−
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 two way switching, but not two way brightness control.  
+
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. (although note that as a straight replacement for an existing switch, a dimmer will always be a little cheaper to run if nothing else is changed)
 
 
* 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

Switchbank new 1083-6.jpg
GEC-grid-1.jpg
GEC-grid-2.jpg
GEC-grid-3.jpg
MK-grid-1.jpg
MK-Grid-2.jpg


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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