For decades dimming a light was a really simple process. Incandescent and halogen bulbs provided a smooth and wide range of dimming, from very low to very bright, using standard mains dimming rotary switches. This dimming technology was relatively cheap, easy to fit, and a smooth flicker free dimming experience was guaranteed.

However, the inefficiencies of incandescent and halogen bulbs has driven the rise of LED lighting technology. The average incandescent bulb has a luminance efficacy of between 10 – 20%, that means as little as 10% of the energy used produces a visible light, the other 90% is used generating heat. That’s a lot of wasted energy! So it’s no bad thing really that these inefficient light sources are slowly being removed from sale.

This is where the humble LED comes into its own. Having been around for many years, usually as the little red dot on your electronic device, lighting manufacturers sought to advance this technology in order to make it a commercially viable light source to replace the old incandescent and halogen bulbs. Early lights were very expensive and unreliable, but manufacturers have been advancing commercially available LED lights for many years now, which has brought the cost down significantly and increased the reliability exponentially, meaning we can now expect to pay £7-£10 for a good quality LED bulb which should last for around 20,000 hours. In comparison an incandescent bulb might only last for 1000 hours of use.

LEDs use far less energy to produce an equivalent level of light, so a 5w LED can potentially produce the same light output as a 60w incandescent which is clearly a big reduction in energy usage. However LEDs still only have a luminance efficacy of 40 – 50 % which means even though it might only be consuming 5w of energy, 50% of that energy is still being lost as heat.

There are other complexities as well, which had to be overcome to make LED lights viable for the mass market, not least the fact that LEDs are low voltage DC (Direct Current) devices, and our homes run on a 230v AC (alternating current) power system. So there’s a lot going on in that little LED bulb or driver to take the mains voltage and covert it not only to low voltage, but also from AC to DC. It’s definitely far more complex than passing mains voltage through a tungsten wire, which is exactly how incandescent and halogen bulbs work.

Another issue which faces LED bulbs is the colour of the light they produce. We are all very used to the yellowish white an incandescent bulb gives out, and as that light is dimmed the light becomes more yellow and even goes into an orange hue when dimmed really low. This light profile is very comforting to us as human beings, and actually plays into our circadian rhythm as it’s similar to the way the sun changes its colour and light intensity as it goes down.

In the main we’ve never really had to worry about the colour of our lights as it’s always been the same and we haven’t had a choice. But with LED we now have this notion of colour temperature, so when you go to buy an LED bulb it might say Warm White 2700k, or Cool White 5000k. The colour measurement is all based on the colour of hot metal using the kelvin scale, which is what the k stands for, 5000 – 6000k is generally perceived to be the colour of natural day light depending on where you live, and 2700k is around the same as an undimmed incandescent bulb. So you now get to choose the colour of your light as well as the brightness. Some people see this as a positive thing for LED and others just think it’s adding complexity to something which was very simple.

We now have cost effective, high quality LED bulbs, which use a fraction of the energy our old bulbs used to, they last 20x longer and we can pick the colour temperature to suite our needs. Problem solved right, no need to worry about inefficient incandescent or halogen bulbs anymore?

Not quite! Whilst it’s true that LED is definitely great for replacing traditional mains voltage bulbs which don’t need to be dimmed. There are further complexities in replacing low voltage bulbs such as MR16 type spot lights, and when it comes to dimming LED bulbs this can be whole world of pain!

Let’s start with low voltage MR16 spot lights, as these have been installed in their millions around the country, and are essentially a low voltage version of a GU10 spot light. Whilst you can buy very good quality LED MR16 bulbs, this is only half of the story. All MR16 bulbs have a transformer (or driver) which takes the 230v AC mains voltage and converts it to 12v AC low voltage, the issue when it comes to converting these lights to LED, is in the drivers ability to operate an LED bulb. Time and again people have issues with the bulbs not working at all or them only working for a short period of time before going pop. This is mostly due to the fact an old driver will have a minimum load requirement to make it work, this isn’t a problem with one or more 50w or even 30w halogen bulbs attached, however you change all those bulbs to 4w LED equivalents, now the driver doesn’t have enough current draw to make it work properly, this either means the lights will just not work, or it will over drive the LED bulbs which will make them go pop after a few hours of use, this is usually accompanied by lots of humming or buzzing to further add to the problem. 

As a rule of thumb if you have an old electronic transformer, this will likely have a minimum load requirement and will be problematic if you change to LED bulbs. If you have older magnetic transformers these don’t tend to need a minimum load and cope much better with replacement LED bulbs. You can usually tell what type you have just by looking at what’s written on the top if you can get to the transformer. However the best option to ensure smooth operation is to replace older transformers with new LED drivers specifically designed for the job, that way you can ensure no flicker, humming, buzzing or short life issues with your new MR16 LED bulbs.

Now to dimming, as described at the beginning of this article, dimming used to be a very simple job with incandescent and halogen bulbs. In general this would be achieved through a rotary dimmer switch by using leading edge based dimming, which cuts up the electricity supply to the bulb 50 times a second giving the dimming effect. This dimming technology works flawlessly with Incandescent and halogen bulbs, providing a dimming range from barely on to full brightness, without any flicker at any level.

Then we bring dimmable mains voltage LED into the equation, and this starts to play havoc with our once perfect dimming technology. First things first, not all LED bulbs are dimmable, you need to make sure that the LED bulb you have contains the technology required to be dimmed. Providing the bulb is dimmable, we than have the challenge that not all dimmable LED bulbs are compatible with a traditional leading edge dimmer switch, and in turn most leading edge dimmers require a minimum load to work properly. So by changing all your bulbs to LED on your old dimmer you might actually find that when dimmed the bulbs flicker and buzz and just generally don’t dim very well.

So what’s the answer? In general a trailing edge dimmer switch will help significantly with dimming mains LED bulbs, but you need to be careful when picking a dimmer switch. All dimmer switches have a load rating; 50, 100, 250, 500, 1000 watts etc. However this rating is for an incandescent load and not an LED load, to get the correct LED load you need to divide the maximum load by 10, this is because of the very high inrush current required by LED bulbs. So for example a 250w trailing edge dimmer will be rated for up to 25w of LED bulbs. Good news then, replace all your dimmers with trailing edge and you’re good to go? Not quite! Even with a trailing edge dimmer you still aren’t guaranteed flicker free dimming all through the dimming range and this is to do with how the mains dimming signal is converted by the bulb to something the LED understands. Higher quality bulbs tend to be better at it than cheaper ones.

Another challenge with dimming mains LED bulbs is their low level dimming performance. In general most common mains LED bulbs will not dim below 10% and in a number of cases won’t dim below 30%. This can be a significant problem when you’re trying to create an ambience in a room. The other challenge is colour temperature. An LED bulb in general will maintain it’s colour temperature as it dims down, this is something that can be quite disconcerting to people having been used to the way an incandescent bulb becomes more yellow and even orange as it dims, leading to a dimmed LED not feeling as warm and comforting as a dimmed incandescent bulb.

How do we get around this little problem? Well from a colour temperature perspective a number of manufacturers now make a range of bulbs which change their colour temperature as they dim down (dim to warm), trying to mimic the good old incandescent bulb. This definitely helps improve the dimming effect, but often the colour temperature at the lower end is far too orange, still it’s a step in the right direction. In terms of the low level dimming there isn’t an easy answer to this as it’s a limitation of the LED bulb itself, manufacturers are constantly improving the dimmability of their bulbs but I’m not sure mains dimming LED will ever give the same performance as the old incandescent bulbs.

Is that it then, are we stuck with worse dimming now with LED? In terms of mains dimming the answer at this time is yes, although technology is moving forwards all the time. However there is another way! Low voltage dimming is the best way of dimming LED lights. There are a number of low voltage dimming options available, but these really need to be planned into a lighting design and aren’t always that easy to retrofit. That being said if you are having a major renovation or building a new house then you should definitely be considering installing a lighting system which uses low voltage dimming technology.

There are a number of different low voltage dimming options on the market, the most common ones are 0 – 10v, DALI (digital addressable lighting interface) and DMX 512. The one thing all these technologies have in common is their ability to provide smooth flicker free LED dimming, and with some, the ability to dim to the low levels an incandescent bulb was capable of. So let’s take a quick look at the options and their benefits:

0 – 10v

0 – 10v is an analogue dimming system, which uses a DC low voltage signal (1v – 10v) to tell the bulb what dimming level to use.  The system requires 2 extra control wires which go from the switch to the driver or light fitting, the 2 low voltage control wires must be kept separate from the mains cables to ensure there is no interference or inductance. The dimming range is very good when compared to mains dimming and is also a lot smoother, however the minimum level of dimming that can be achieved is 10% (or 1v), anything below this is considered off.

This technology is relatively inexpensive and is easy to design into a new project or renovation.


DALI or Digital Addressable Lighting Interface is a very flexible and adaptable lighting technology. This is a digital dimming technology allowing for up to 255 different levels of dimming. The system uses an extra 2 wires the same as 0 – 10v however this time the 2 control wires can be run in the same cable as the mains voltage. The dimming range of a DALI system is exceptional, and is as good as an old incandescent bulb and dimmer. The other benefit of DALI is that each light can have its own address on the system, meaning you can change the configuration of the lights as the room or your needs change.

As an example if you had 8 spot lights in the ceiling, in a traditionally wired or even 0-10v wired system all lights might come on, go off and dim down together, and if you ever wanted to change this that would require physical rewiring of the lighting. With an individually addressed DALI lighting system each light can be programmed, so you can change how the lights are grouped together through software rather than physical rewiring. This can save a lot of mess and provide infinitely more flexibility in lighting design when compared to traditional lighting.

DALI is more expensive than traditional or 0 – 10v lighting and does need to be designed into a project or renovation early on. It will also usually be connected to a lighting control system.

DMX 512

DMX 512 actually comes from the entertainment industry, and is used to control complex lighting systems, like those used in theatres and music concerts. Its primary use in the residential lighting space is to control the colour of lights. It’s a digital dimming technology and has all the same benefits of DALI, with the added bonus of being able to control the colour of the light by mixing red, green and blue LEDs to create nearly any colour you can think of.

DMX 512 can be very expensive and has to be designed into any project at a very early phase. It’s unlikely a whole house would be wired in DMX 512, instead it is usually used to control statement lighting in certain areas where colour or movement control are required.


Whilst the introduction of LED lighting has undoubtably been a very good thing in terms of saving energy, it has brought with it some other complexities which we just didn’t have to think about with the humble incandescent bulb. This added complexity can be frustrating and bewildering to people who just want to achieve something which used to be so simple.

There is help at hand though! By contacting a company like AGW Technologies who understands LED lighting technology, we can guide you through the jargon and complexity, and deliver you a high performance lighting system which is both energy efficient and simple to use. So why not give us a call to find out what we can do for you.