Dimming LED Lamps

Replacing a traditional incandescent or halogen lamp for an LED equivalent used to be a real challenge. Over the last few years, lighting manufacturers have done a fantastic job recreating almost every style of lamp in an LED format. LED lamps can now match existing size footprints and colour performance with the benefits of long lamp life and substantial energy savings. The one area which still needs careful attention when looking to replace a halogen or incandescent lamp is dimming.

by Gordon Routledge
Monday 26th October 2020

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Why should you dim LEDs?

Dimming lighting can transform the look and feel of a room. With the flick of a switch, a room can change from a workspace to a relaxing place. With more of us working from home, being able to adjust lighting levels to match the task is increasingly essential.

VIDEO - NEW Series: The complete guide to LED lamp dimming

What's the problem with dimming LED lamps?

Dimming an LED lamp with a traditional dimmer is always a compromise. The lamps include an electronic driver which manages the power flow to the LED light source. The electronics within the driver circuit performs a tricky juggling act of maintaining a stable light output, with no flashing or flickering, and recognising the need to dim when connected to a dimmer switch. LED lamp manufacturers have done a remarkable job in making LED lamps work with old lamp dimmers. However, most LED lamps won't dim to a low level when connected to an older style dimmer.

If you are changing halogen lamps to LED lamps, then you will probably have to change the existing dimmer switch. Even with a new dimmer switch designed for LED lamps, you will need to set the dimmer to match the LED lamp. Setting a lamp to match a dimmer switch usually involves selecting a mode of operation, leading or trailing edge, and setting the lowest point the dimmer will keep the lamp illuminated.

VIDEO - Leading edge or trailing edge dimmers?

Lamp and dimmer compatibility

Lamp manufacturers will often publish a list of dimmer switches which they have tested with their lamps. A compatibility chart should list the dimming range (light output range), the number of lamps which can be connected and the dimming mode required.

LED tape cut points — LED lamp compatibility chart (Aurora Lighting)

Setting the low-end light level

If you're lighting a living room, bedroom or kitchen, achieving a smooth dimming to a low light level is essential. While most dimmer and LED lamp combinations will work out of the box, setting the low-end cut off point can make a huge difference.

When adjusting the low-end cut-off, you are stopping the lamp going into an unstable state e.g. flickering. You can also prevent the lamp from going out as you turn down the control knob.You may also find that you enable the lamp to dim to a lower level.

Every lamp is our test setup was different and required some dimmer adjustments to eliminate low end flickering or expand the lighting level range. The method to set the low-end cut off differs between dimmer manufacturers. Some dimmers have a small potentiometer on the wiring side. Others have a set-up mode accessed by turning and pressing the control knob in a specific sequence.

VIDEO - Setting up low end dimming

low end dimming trimming — Setting low end light level

Dimming problems

Follow the advice in this series, and you should be able to achieve a reliable LED lamp installation with smooth dimming to a stable low level. If you are joining us late or have inherited a troublesome installation here are some of the common problems.

Dimming problems: Why is my LED lamp noisy?

Noise

You'll often hear a buzzing or humming noise in the lamp, dimmer or both at the same time. An old trailing edge dimmer will often buzz even on old incandescent or halogen lamps. An incompatible dimmer usually causes noisy lamps.

1: Check LED lamp compatibility with the lamp manufacturer and replace dimmer with a recommended dimmer. Trailing-edge dimmers are usually quieter.

2: Check the dimming mode. Most LED dimmer switches have a few modes of operation. Most LED lamps work best on a trailing edge dimming waveform. Some dimmers will auto-detect the lamp and adjust automatically; others need to be manually set.

Dimming Problems: Why does my lamp flash?

Flashing or flickering

The same issues can cause a flickering lamp as a noisy lamp. A lamp which doesn't dim but only flashes is usually non-dimmable.

1: Check the lamp dimmable

2: Has the low-end dim level been set correctly. Adjust the low end to increase the light-out slightly until the lamp stops flickering.

Something special dim to warm LED lamps

VIDEO - Dim to warm LED lamp technology

Incandescent and halogen lamps subtly change colour when dimmed. You may recognise the more orange look of a cosy restaurant at night. LED lamps don't change colour when dimmed, and this is often a reason people preferred incandescent lamps. If you want to replicate the look and feel of dimmed incandescent lamps, then look out for lamps with a variable colour temperature.2200K (the dimmed orange) to 3000K (full output) Also referred to as dim to warm, warm dim of Philips DimTone which we used to make our video.