An electrician fitted a "200W" dimmer to a run of six 10W LED downlights, well under the number printed on the box, and it buzzed and flickered from day one. The dimmer wasn't faulty. The 200W rating was for mains halogen, and the same switch's actual LED capacity was a fraction of that figure, buried in the small print he'd never opened.

Why the Big Number on the Box Is the Wrong One

Dimmer switches are rated for the maximum load they can safely control, and that figure was set decades ago against halogen and incandescent bulbs, which draw current in a simple, predictable way. LED drivers behave completely differently, drawing power in short pulses rather than a steady curve, which is why a dimmer built to switch 200W of halogen often only handles a fraction of that in LED wattage, sometimes as little as 5W minimum load.

Manufacturers print both figures, but the halogen number is usually the larger, bolder one on the packaging, since it's the higher figure and was the industry standard for longer. The LED rating, the one that actually applies to almost every installation today, is often the smaller print next to it or on the spec sheet, not the box front.

Getting the Sum Right Before You Order

The calculation itself is simple once you're using the right numbers. It's the habit of reading the halogen figure and assuming it applies to LED that causes most underload and overload returns. Working from actual bulb wattage, not fitting count or the bold number on the box, avoids the comeback callout.

• List every bulb on the circuit and its actual wattage, not its brightness in lumens
• Add the wattages together to get total circuit load
• Compare that total against the dimmer's LED-specific rating, both minimum and maximum, not the halogen figure
• If the total sits below the minimum LED load, either add fittings to the circuit or choose a dimmer with a lower minimum rating

If flickering has already shown up on an existing install, our LED dimmer flickering guide covers the fixes once the wrong load is confirmed, and our trailing edge vs leading edge guide covers which dimming technology to pick alongside getting the wattage right. Our full light switches range has standard and dimmer options side by side if the spec is still open.