At a glance
| Question | Short answer | Basis |
|---|---|---|
| What the driver decides | Which dimming methods the fitting accepts, its lowest level, whether it hums or flickers, and much of its life. | Our dimming sheet; DOE, 2014 |
| Where it can live | In each lamp, inside the fitting, or remote in a void or cabinet. | CIE ILV 17-27-055, 17-28-053 to 17-28-055 |
| Replaceable? | In Great Britain, separate control gear in a containing product must be replaceable with commonly available tools, unless the technical documentation justifies otherwise. | SI 2021/1095 reg 6(1) and (2) |
| Mains or low voltage? | The mains side is fixed wiring for a competent electrician. Extra-low voltage is not over 50 V a.c. or 120 V ripple-free d.c. | Approved Document P, App. A; BS 7671 |
| What fails first? | More often the driver than the LED, in the tests we read. | DOE, 2014 and 2013 |
| How far away? | As far as the data sheet and the voltage drop allow. Ask for the maximum run in writing. | Ohm's law; the data sheet |
| Standards to name | BS EN IEC 61347-1:2024 and 61347-2-13:2024 (safety), BS EN IEC 62384:2020 (performance), BS 7671:2018+A4:2026 (installation). All listed current by BSI; not read. | BSI Knowledge |
Rules and standards as read on 5 November 2026. Standards were listed, not read: check the current editions.
What the driver decides, and three places it can live
In most decorative luminaires the driver, not the glass or the LED, decides what the fitting can be dimmed by and how long it lasts. The CIE International Lighting Vocabulary defines control gear as a unit between the power supply and a light source that supplies it with its rated voltage or current, and says it can include dimming, power factor correction and interference suppression. An LED driver is LED control gear. A US Department of Energy lifetime guide says driver electronics can be as important a reliability concern as the LED sources, sometimes more, and that driver failure is likely to be an eventual cause of abrupt failure, although long-lived drivers are available.
The first decision is where it lives. The three arrangements below are the usual ones for a chandelier, pendant or wall light. In the Great Britain lighting regulations, a separate control gear is a control gear that is not physically integrated with a light source and is placed on the market as a separate product or as part of a containing product; so in arrangements B and C the driver is usually separate control gear, and in A it is not.
| Arrangement | What it is | What you gain | What to watch |
|---|---|---|---|
| A. In each lamp | Mains is fed to the lamp holder. Each LED lamp carries its own control gear (CIE: an integrated LED lamp, designed for direct connection to the supply voltage). | Standard lamps; any lamp can be swapped; nothing to hide. | Dimming is set by each lamp, so mixed lamps may not dim together. The lamp's life is its driver's life. |
| B. In the fitting | One driver in the canopy or body feeds the light sources. CIE separates built-in control gear (designed to be built into a luminaire) from integral control gear (a non-replaceable part that cannot be tested separately). | One product; short wiring. | Heat and weight sit at the canopy. Reaching it may mean lowering the fitting. If it is integral, replacing it is repairing the fitting. |
| C. Remote | A driver away from the fitting in a ceiling void, plinth or cabinet, with an extra-low-voltage cable between. CIE: independent control gear can be mounted separately outside a luminaire; for semi-integrated LED modules the power supply of the control gear is on a distant location. | A slimmer, lighter fitting; heat away from the glass; a hatch can be sized for service. | Cable run and voltage drop; two trades; the hatch; a label on every run. |
The definitions are from the CIE vocabulary and SI 2021/1095. Which arrangement suits a piece is for the lighting designer and the partner workshop; no source ranks them.
Where to put a remote driver
The drawing shows the principles for a driver away from the fitting. It is schematic: sizes and clearances come from the driver's data sheet and the electrician, never from the drawing.
- Reachable. Put it directly above a hatch in the ceiling, or in a plinth or cabinet bay with a removable panel, fixed with screws or magnets, not glue. Size the hatch from the driver's dimensions plus room for hands and tools: [ ] mm by [ ] mm. We give no universal figure, and the hatch is drawn on the shop drawing and recorded in the handover pack.
- Cool and with clear air. The DOE guide says the failure rate of electronic parts relates to their temperature, so the design should account for the power supply's heat as well as the LED's, and that the supply's temperature rating should suit the expected surroundings. It quotes the old rule of thumb that 10 degrees Celsius less operating temperature can double a component's life, and calls it an over-simplification that is still useful. So do not bury a driver in insulation or a sealed box, and keep it away from other heat sources.
- Isolatable. A switched spur or isolator within reach lets the electrician make it safe before the hatch is opened. The wiring rules are in BS 7671, which we did not read.
- Close enough. The table shows why the cable run matters. The limit for your driver is on its data sheet: ask for the maximum cable length and the output voltage window in writing.
- Quiet. Some driver and dimmer pairings hum at low levels, as our dimming sheet notes. Ask for the fitting's noise at its lowest level and keep a driver away from the head of a bed or a quiet corner where it can be avoided.
- Not hung from the fitting. The fixing for the fitting is the structural engineer's. Fix the driver to the structure or a bracket of its own, not to the chain.
- Sequenced. The electrician runs the mains to the driver position first, and connects, tests and certifies after the driver and fitting are in. Agree who does each, and when.
Cable run and voltage drop, worked on example values
Current is power divided by voltage, and the voltage lost in a cable is that current multiplied by the cable's resistance, which is paid in the out and the return conductor. The table assumes an example conductor resistance of 12 milliohm per metre and a 60 W fitting. Both are assumptions for the worked table, not a cable's data. A 12 V supply carries twice the current of a 24 V supply for the same power, so for the same cable it loses four times the percentage.
| Supply | Current for 60 W | 2 m run | 5 m run | 10 m run | 15 m run |
|---|---|---|---|---|---|
| 24 V | 2.5 A | 0.12 V (0.5%) | 0.30 V (1.2%) | 0.60 V (2.5%) | 0.90 V (3.7%) |
| 12 V | 5 A | 0.24 V (2.0%) | 0.60 V (5.0%) | 1.20 V (10.0%) | 1.80 V (15.0%) |
Example figures only: 12 milliohm per metre per conductor and 60 W are assumptions. The percentages are not limits. With a constant-current driver the cable uses up part of the driver's output voltage window instead of simply dimming the load, so the limit is what the data sheet says.
Driver types and the dimming pairings to check
A driver is built for a type of load and a type of dimming signal, and the pairing is what has to be checked. The BSI listing for BS EN IEC 62384:2020 says control gear for LED modules in that standard is designed to provide constant voltage or constant current, and that deviations from the pure types do not exclude it. The table sets out the families and the questions that go with each. It is practice, set against the data sheets, and it gives no brand or product.
| Driver | Output | Feeds | Dimming input it can take | Check before you specify |
|---|---|---|---|---|
| Constant-current driver (mains in) | Holds the current; the voltage settles within a stated window | LED boards and modules whose maker states a current | As the data sheet states: none, phase-cut, 0-10 V, DALI-2 | Rated current matches the module; the module's voltage sits inside the driver's window; the lowest dimming level |
| Constant-voltage driver (mains in) | Holds a voltage, for example 12 or 24 V | Strips and modules that limit their own current | As above | Rated voltage matches; the load sits between the driver's minimum and maximum; voltage drop on the cable |
| Phase-cut dimmable | Either of the above | Fittings on a mains dimmer | Forward (leading-edge, TRIAC) or reverse (trailing-edge) phase-cut dimmer | Which edge type; the dimmer's minimum load; how many drivers per dimmer (see the dimming sheet) |
| 0-10 V dimmable | Either of the above | Fittings on a low-voltage control pair | A 0 to 10 V d.c. signal on two control wires, separate from mains | Sinking or sourcing; the lowest level; how off is made (often by switching the mains); polarity |
| DALI-2 | Either of the above | Fittings on a digital bus | Addressed digital commands (IEC 62386) | Driver listed in the DALI Alliance database; addresses used per fitting; bus power and cable limits |
| DMX512 or wireless | Either of the above | Scene-controlled fittings | Through a driver with that input, or a decoder or receiver in or on the fitting (our reading) | Which of the two; where the receiver sits and what powers it |
| Emergency | Outside this sheet | Escape and standby lighting | Not covered | The emergency lighting designer; BS 5266-1 was not read |
For the numbers behind phase-cut, 0-10 V, DALI-2 and DMX512, such as the loads a dimmer carries or the limits of a DALI bus, see dimming protocols for decorative lighting; we do not repeat them here. Whatever is chosen, ask the workshop to state per fitting:
- the driver type, rated output and rated load, and the dimming inputs its data sheet accepts;
- how many independently controlled outputs the fitting has, and how each is wired and labelled;
- the lowest light level it reaches with that driver and light source, and whether it flickers or hums there;
- the driver's ambient temperature limit, and its stated life at that temperature;
- whether the same driver will be available later, and the part number to order.
What fails, and how to design it out
The sources we read point at the driver. A DOE lifetime guide says that driver failure is likely to be an eventual cause of abrupt failure in LED devices, that capacitor failure is a leading cause of driver failure, and that derating components extends life. A DOE Hammer Test report put 611 LEDs through temperature shock and power cycling and saw four LED failures, under 1 per cent, while the failures that did occur were typically in the driver circuit, board-level failures being most common, and at the connector between the driver and the LED board. Those were general-lighting luminaires, not decorative pieces, and the documents are dated 2014 and 2013, so we take the direction and not the numbers.
| Failure point | Why it happens | Design response | Basis |
|---|---|---|---|
| Driver runs hot and ages early | Heat in an enclosed space; load close to its rating | A ventilated void; load well below rating, [ ] per cent; the data sheet's ambient limit | DOE 2014 section 3.2; the percentage is practice |
| Capacitor wear | DOE names capacitor failure a leading cause of driver failure | Ask for the driver's stated life at its working temperature and its warranty; prefer derated parts | DOE 2014 |
| Flicker, hum or drop-out when dimmed | Driver and dimmer or controller not matched | Specify them together; try one fitting over its whole range | Our dimming sheet |
| Overloaded dimmer or bus | Circuits sized on lamp watts, not on driver load | Count drivers per circuit on the schedule | Our dimming sheet |
| Dim far end, or a driver that cannot reach | Voltage lost on a long, thin, low-voltage run | A shorter run, a higher voltage or a thicker cable, within the data sheet's maximum run | Ohm's law; the table |
| Failed joint or connector | Strain, heat and vibration at the driver-to-LED connection | A plug connector at the hatch, strain relief, no joint behind fixed finishes | DOE Hammer test: failures at the driver circuit and its connector |
| Wrong driver fitted on replacement | Model discontinued; no record of which was fitted | Label the model on the driver; keep a spare; record it in the handover pack | Practice; SI 2021/1095 reg 6(4) |
| Driver cannot be reached | Built in behind finishes; the fitting must be lowered | A hatch on the shop drawing; a service loop; a target replacement time written down | Practice; our lit joinery sheet |
The live article Hotel lighting design says that specifying replaceable LED modules and standard drivers rather than sealed units makes the difference between a fixture that lasts ten years and one that lasts three. We found no source for those two figures and do not repeat them.
The rules and standards that touch the driver
Replaceability and ecodesign (Great Britain)
The Ecodesign for Energy-Related Products and Energy Information (Lighting Products) Regulations 2021 (SI 2021/1095) define a containing product as a product containing light sources or separate control gears, and say it includes luminaires that can be taken apart and furniture containing light sources, for example display cabinets (regulation 2(10)). Regulation 6(1) requires manufacturers, authorised representatives and importers of containing products to ensure that light sources and separate control gears can be replaced with commonly available tools and without permanent damage to the containing product. Paragraph (2) lifts that where the technical documentation gives a justification related to functionality. Paragraphs (4) to (6) require information on replaceability on a public website and, for products sold directly to end-users, on the packaging and in the instructions, and dismantling instructions for end of life. Schedule 3, paragraph 2, sets minimum full-load efficiency for separate control gear for LED light sources (by a formula in the declared output power), and says the standby power of a separate control gear must not exceed 0.5 W. Whether and how this applies to a bespoke fitting, who its manufacturer is, and what the exemptions in Schedule 4 cover are not settled by what we read: see lighting built into joinery, which sets out the same questions, and take compliance advice.
Standards for the driver
BSI Knowledge lists BS EN IEC 61347-1:2024 (controlgear for electric light sources, general safety requirements; published 31 January 2025; current) and BS EN IEC 61347-2-13:2024 (electronic controlgear for LED light sources, safety; published 31 December 2024; current), and BS EN IEC 62384:2020 (performance requirements for DC or AC supplied electronic controlgear for LED modules; published 31 July 2020; current). The listings say the safety parts cover supplies up to 1 500 V d.c. or 1 000 V a.c., and that performance is covered by IEC 62384, whose tests are type tests. The 2006 edition of BS EN 62384 is withdrawn (6 December 2023). We did not read any of these, so no clause or limit is quoted. Ask the workshop for the driver's declaration of conformity or test report naming the standards and editions; see luminaire conformity for the fitting's own paperwork.
Installation
The wiring standard is BS 7671; BSI Knowledge lists BS 7671:2018+A4:2026, published 15 April 2026, as current. Approved Document P (England, dwellings, 2013 edition) says electrical installations should be designed and installed in accordance with BS 7671 (paragraph 1.1, which names the 2008 edition with Amendment 1:2011, so the reference is dated), that fixed equipment and prefabricated modular wiring linked by plug and socket connectors are within Part P but notifiable only if they involve the work in regulation 12(6A) (paragraphs 2.7 to 2.9), and that non-notifiable work should be designed, installed, inspected, tested and certificated to BS 7671 (paragraph 3.13). Appendix A defines extra-low voltage as not exceeding 50 V a.c. or 120 V ripple-free d.c., whether between conductors or to earth. Part P is written for dwellings; other buildings fall under other rules we did not read, and BS 7671 remains the standard. The mains feed to a driver is fixed wiring; the extra-low-voltage cable beyond it is often installed with the fitting, but the electrician who certifies the installation decides what is acceptable.
Specification wording
Paste into your schedule or specification and replace anything in [square brackets] with your own figures. Wording is a starting point: your specification governs.
Driver for [fitting reference]: [constant current / constant voltage], rated output [ ] mA or [ ] V, rated power [ ] W, with the fitting's load not more than [ ] per cent of that rating. Dimming input: [DALI-2 / 0-10 V current-sinking / trailing-edge phase-cut / none]. Make and model [ ] stated on the shop drawing. Driver to comply with BS EN IEC 61347-1, BS EN IEC 61347-2-13 and BS EN IEC 62384 [edition in force], with the declaration of conformity or test report supplied.
Driver located [in the ceiling void above / in the plinth bay], reached through a hatch not smaller than [ ] mm by [ ] mm fixed with [screws / magnets], with clear air [ ] mm around it and no insulation over it. A switched spur or isolator within reach of the hatch. Maximum cable run to the fitting [ ] m, within the driver data sheet's limit; cable [type, size]; voltage at the fitting not less than [ ] per cent of the driver output. Plug connector at the hatch; no joint behind a fixed finish; label on every run.
[Controls supplier] is to confirm in writing that the driver and the [dimmer / controller] are compatible, the number of drivers per [dimmer / bus] [ ] and the lowest level achieved [ ] per cent. One fitting is to be tried on the real control chain over its whole range and signed off by [lighting designer] before production. A change of driver after approval of the shop drawing is a variation.
The driver is to be replaceable with commonly available tools, without damage to finishes, by [electrician] in not more than [ ] minutes. Spares: [ ] of each driver type, with the model labelled on each driver. Driver warranty [ ] years from [handover]. Handover pack to include driver data sheets, declarations of conformity, a wiring diagram and a schedule of driver positions and hatches.
Terms used on this page
- Control gear (LED driver)
- A unit between the power supply and a light source that supplies it with its rated voltage or current; it can include dimming. An LED driver is LED control gear (CIE ILV 17-28-048).
- Separate control gear
- In SI 2021/1095, a control gear not physically integrated with a light source and placed on the market as a separate product or as part of a containing product.
- Constant current, constant voltage
- BS EN IEC 62384 describes LED control gear as designed to provide constant voltage or constant current. A constant-current driver holds the current and a constant-voltage driver the voltage.
- Extra-low voltage
- A voltage not exceeding 50 V a.c. or 120 V ripple-free d.c., whether between conductors or to earth (Approved Document P, Appendix A).
Standards and sources
- SI 2021/1095, Ecodesign (Lighting Products) Regulations 2021, regs 2 and 6, Schedule 3 para 2: read 5 Nov 2026.
- Approved Document P, Electrical safety, Dwellings, 2013 edition (England): paras 1.1, 2.7 to 2.9, 3.13, Appendix A.
- BS EN IEC 61347-1:2024 and BS EN IEC 61347-2-13:2024; BS EN IEC 62384:2020; BS 7671:2018+A4:2026: current per BSI Knowledge; not read; check editions.
- CIE S 017:2020 International Lighting Vocabulary (e-ILV): terms 17-27-055, 17-28-048 to 17-28-056.
- US DOE: LED Luminaire Lifetime (3rd ed., Sept 2014); Hammer Testing Findings for SSL Luminaires (Dec 2013): dated; general-lighting luminaires.
Questions we are asked
Where should the LED driver for a chandelier go?
Where it can be reached and kept cool: in the canopy, if the canopy is large enough and the fitting can be lowered, or remote in the ceiling void directly above a hatch, or in a plinth bay or cabinet. Avoid burying it in insulation or a sealed box. Put a switched spur or isolator within reach, label it, and draw the hatch on the shop drawing.
How far can the driver be from the fitting?
As far as the driver's data sheet allows: ask the workshop for the maximum cable length and output voltage window in writing. The voltage lost in the cable is the current multiplied by the cable's resistance, so a 12 V supply loses four times the percentage of a 24 V supply for the same cable and power. The worked table on this page uses example values only.
What is the difference between a constant-current and a constant-voltage driver?
A constant-current driver holds the current to the load and lets the voltage settle within a stated window; a constant-voltage driver holds the voltage, for example 12 or 24 V, and the load limits its own current. BS EN IEC 62384 covers control gear designed to provide constant voltage or current. Which you need depends on the LED board or module, so take it from the maker's data sheet.
Why does my chandelier flicker or hum on the dimmer?
Usually because the driver and the dimmer or controller are not a matched pair. The driver is built for particular dimming signals, so specify them together and try one fitting over its whole range before production. Our dimming protocols sheet sets out the checks.
How long does an LED driver last?
We found no figure from a source we read for decorative fittings. A DOE lifetime guide says driver failure is likely to be an eventual cause of abrupt failure and that long-lived drivers are available, and that heat and component derating matter. Ask the workshop for the driver's stated life at its working temperature and its warranty.
Does a driver have to be replaceable?
In Great Britain, regulation 6(1) of SI 2021/1095 requires manufacturers, authorised representatives and importers of containing products to ensure that light sources and separate control gears can be replaced with commonly available tools and without permanent damage, unless a technical justification is given in the documentation. Whether that reaches a bespoke fitting is not settled by what we read, but it is the safe specification either way.
Does the driver need an electrician?
The mains feed to a driver is fixed wiring and is for a competent electrician working to BS 7671. In dwellings in England, Approved Document P puts it within Part P, notifiable only for the work regulation 12(6A) names. Extra-low-voltage cabling beyond the driver is often installed with the fitting, but check with the electrician who certifies the installation.
Download the factsheet
A two-page A4 PDF with the driver and dimming pairings, the remote driver drawing, failure points and paste-in wording for the driver, its place and its documents, to keep with your project file.