Most under-cabinet and wardrobe lighting failures are decided before anyone looks at a price list. The light is the wrong size for the cavity, the driver is undersized for the run, or the sensor was chosen from a feature list instead of from the way the cabinet opens. This article sets out the four decisions that fix the product: cavity, run length, driver and sensor. Get those right and what remains is finish and paperwork.
Start From the Cavity, Not the Catalogue
Measure the space the light has to live in before you choose the light. Three dimensions matter: the clear depth behind the cabinet floor or shelf lip, the height available inside the cabinet, and the length between the end panels.
- Recessed: an aluminium profile set into a routed groove disappears almost completely, but the groove has to be cut at the factory. Confirm the profile width and the material that remains around it.
- Surface mount: a slim bar or strip fixed underneath needs only a few millimetres of height and is the fastest option, but it stays visible when the cabinet is open.
- Shelf: glass and thin shelves usually need the light at the front edge or built into the shelf, because a rear-mounted strip throws a hard shadow towards the user.
A light that is 2 mm too tall for the cavity will be fitted anyway, usually by bending a bracket, and that is where noise and early failure begin.
Match the Driver to the Whole Run
Low-voltage cabinet lighting is a system: fixtures, driver, connectors, splitters, cable and sensor all sit on one circuit, and the driver has to be sized for the total connected load rather than for a single light.
- Add up the rated power of every fixture on the circuit.
- Add the losses of the cable and connectors over the real run length.
- Leave headroom so the driver is not run at its ceiling inside a closed cabinet, where the ambient temperature is higher than in the room.
- Check that the chosen sensor or dimmer is compatible with that driver; not every sensor switches every driver cleanly.
Where a supplier does not publish a driver matching range, ask for it in writing. A driver chosen by trial and error is the most common reason a run flickers, buzzes, or fails in its second year.
Voltage Drop Is the Usual Reason a Long Run Looks Uneven
A 3-metre wardrobe and a 6-metre kitchen run are not the same electrical problem. Current through the cable raises resistance losses, so the fixtures furthest from the driver receive less voltage and appear dimmer or shift in colour. The effect is worse on 12 V than on 24 V, and worse again on thin cable.
| Situation | What to specify | What to confirm |
|---|---|---|
| Run under about 2 metres, one door | Single driver, single feed | Total load and cable gauge |
| Kitchen run of 2-5 metres | 24 V platform, fed from the centre or both ends | Even brightness at both ends, on the real cable length |
| Run over 5 metres, or two separate cabinets | Two drivers, or one larger driver with a distribution block | Where power enters and how the extra cable is hidden |
| Shelf or display case with several levels | Separate feed per level from a splitter | Connector count and access for later service |
A bench test with a short cable proves nothing about a six-metre installation. Ask for the brightness check to be made at the cable length you will actually fit.
Choose the Sensor From the Opening
Sensors are where a good fixture starts behaving badly in the field, because the trigger depends on the opening, the material and the user.
- Door switch or magnetic door sensor: the reliable choice for cupboards, wardrobes and drawers. Confirm the mounting position so the door closes it without pressure and without leaving a gap.
- Hand-wave sensor: useful at a kitchen counter where hands are wet, but it depends on the reflective surface below and on a consistent wave distance. It is the wrong choice for a deep, dark shelf.
- Presence sensor: suits walk-in wardrobes and night lighting. Expect to tune the delay and the standby consumption, and test it with the door open rather than on a bench.
- Touch dimming: convenient on a shelf edge, but sensitive to metal structure and earthing.
Where a simple door switch solves the problem, use it. Control complexity that adds no convenience becomes a service call.
Colour and Finish Decide Whether the Light Disappears
Under-cabinet light is task light; wardrobe light is usually orientation and display. Both are judged by what the user sees, not by lumens on a datasheet.
- Warm white around 2700-3000 K suits wardrobes and timber kitchens; 4000 K suits work surfaces and retail display where colour judgement matters.
- Ask for colour rendering and colour tolerance data, not only a colour temperature. Two batches that both read 3000 K can still look different side by side.
- Match the profile finish to the interior. Inside a dark cabinet, a bright anodised profile is the most visible object in the room.
Look at a sample in your own cabinet material. A photograph cannot settle this.
What the Specification Sheet Has to Contain
Before ordering, a buyer should hold one document per model. It should state:
- input and output voltage, fixture power, and the driver matching range;
- luminous flux or illuminance, colour temperature, colour rendering and colour tolerance;
- sensing method, sensing distance, delay time and standby power;
- fixture dimensions, cable length, connector type and mounting method;
- operating temperature, IP rating, and whether the product suits dry locations only.
If a line is missing, the run will be designed around an assumption.
Send the cavity dimensions, the total run length, the number of doors and the required colour temperature to your supplier, and ask for a full bill of materials in return: fixtures, driver, sensor, splitter, cable, connectors and mounting parts. A run quoted as loose lights rather than as a system is the one that arrives with a missing connector.