Circuit off, measure, take the old dimmer out of the box and move the wires across one to one: the wire from the circuit to the input, the wire to the lamp to the output. With most dimmers that is two wires. Then use the trim screw to set the minimum so the LED bulbs do not flicker at the lowest setting.
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Why the old dimmer has to go
A dimmer from the days of incandescent and halogen usually works with leading-edge dimming and has a minimum load that is too high for LED. The result: flickering at low settings, humming, or bulbs that will not switch off. Where that noise comes from is in Why does an LED bulb or dimmer hum?
A trailing-edge LED dimmer starts at a much lower load and switches more gently. Our 160 and 250 watt dimmers start at 0.5 watts, the universal dimmer at 3 watts.
Calculate first, then buy
Add up the wattage of all the bulbs that will go on the dimmer. Six spotlights of 5 watts is 30 watts. Choose a dimmer whose range comfortably covers that. The universal dimmer goes up to 100 watts of LED, enough for a few spotlights or a pendant light. For more than about fifteen spotlights of 6 watts, the 250 watt version is the logical size. More about choosing is in Which LED dimmer do you need for your spotlights?
Also check that the bulbs themselves are dimmable. A non-dimmable bulb does not work properly on any dimmer.
Does it fit your box and behind your cover plate?
The universal dimmer is an insert module of 71 by 71 by 25 millimeters. It fits a standard back box, and you use the knob and cover plate of your own switch range. According to the manufacturer it has been tested with Berker, Jung, Gira, Peha and Busch-Jaeger. That way the switch still looks the same as the rest of the house.
The replacement step by step
Circuit off and measure. On the terminals of the old dimmer too. See How do you check that the power is off?
Knob and cover plate off. The knob usually pulls straight off. Underneath is a nut or a couple of screws holding the plate.
Dimmer out of the box. Loosen the claws or screws and pull the dimmer forward.
Take a photo. Before you undo a single wire. With a single dimmer you usually see two wires: the live coming from the circuit, and the switched live running to the lamp. On the old dimmer they are often marked L and an arrow or lamp symbol.
Move the wires across. The live to the input of the new dimmer, the switched live to the output. Read the marking on the new dimmer, because it differs per brand.
Dimmer into the box, plate and knob on.
Circuit on and set the minimum. Turn the dimmer to the lowest setting. If the bulbs flicker, turn the trim screw with a small screwdriver until the light burns steadily.
Two switches for one light
If you control the light from two places, for example at the top and bottom of the stairs, you have two-way switching. Then there are three wires on the old dimmer. Our LED dimmers also work in two-way switching: the dimmer in one place, an ordinary two-way switch in the other. On the universal dimmer the two strappers go to L1 and L2.
If you have three or more wires and are unsure which is which, have an electrician do it. A wrongly connected two-way circuit sometimes half works, and that is hard to trace. All dimmers are in accessories.
Can I keep an ordinary dimmer for LED bulbs?
Sometimes it works, but often the bulbs flicker or hum at low settings. A trailing-edge LED dimmer with a low minimum load solves that in most cases.
How many wires does a dimmer have?
A single dimmer usually has two: the live from the circuit and the switched live to the lamp. With two-way switching there are three.
What does the small screw on an LED dimmer do?
It sets the minimum level. Turn the dimmer to the lowest setting and adjust the screw until the bulbs no longer flicker.