A lamp marked dimmable and a bulb marked dimmable can still produce a light that flickers at low levels and buzzes at all of them. The reason is that dimming is not a property of a product; it is a property of a combination.
The three parties
The dimmer, the driver or bulb, and the total load. Compatibility requires the dimmer and the driver to speak the same language, and the load to sit inside the range the dimmer was designed for.
| Dimming method | How it works | Common failure |
|---|---|---|
| Leading edge (TRIAC) | Chops the start of each half cycle | Buzzing, poor low-end control |
| Trailing edge (reverse phase) | Chops the end of each half cycle | Better with LED, less common in old wiring |
| 0–10V | Analogue control pair | Not compatible with residential lamps |
| Integrated driver dimming | Control inside the lamp | Works, but locks the choice of lamp |
Load matters as much as method
A dimmer rated for 600 watts of incandescent load may be unreliable with fifteen watts of LED, because the minimum load needed to keep the triac conducting is not met. Symptoms appear only at the low end, which is why customers report flicker rather than total failure.
The low end is where opinions differ
Dimmers vary in how far down they go before control becomes unstable. If a lamp is expected to serve as a night light, the specification should state a percentage floor and the dimmer should be tested with the exact bulb the customer will use, not a laboratory equivalent.
How to specify it in a programme
Four steps remove most of the risk:
- Fix the bulb or driver the lamp will ship with, and test the dimmer with that unit
- State a minimum load for the lamp, on the packaging and in the manual
- Publish the compatible dimmer types rather than promising universal compatibility
- Where a remote or an in-line dimmer is supplied with the lamp, test the combination as a system
The honest marketing position
A lamp that dims smoothly with the control supplied in the box, and which states which third-party dimmers it has been tested with, is worth more than one claiming universal compatibility. The claim that cannot be true is the one that generates the return.
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