LED Dimming: what’s going on? I was looking for a replacement 1-10v dimmable LED driver and was surprised to hear from my friends that there’s very little call for 1-10v dimming these days. Really? I decided to check out what’s going on with LED dimming these days by asking someone who deals with this on a daily basis.
James King is Sales Director at Mode Lighting, and he’s got me out of trouble more times than either of us care to remember.
To start, let’s remind ourselves of the options that we have when LED dimming is on the agenda. I’ve asked James for his opinion of each of the LED dimming protocols.
Mains Dimming
The oldest dimming method, originally developed for incandescent filament lamps. Its based on reducing the voltage across the lighting load and something that we all know from the rotary and slide dimmers in our homes. It doesn’t require any special wiring as the live wire carries the reduce supply voltage.
All dimmable LED retrofit lamps (GLS, candle, PAR, GU10s etc) are designed to work with domestic dimmers, though BEWARE that not all is rosy in this garden. There is a lot of incompatibility between the electronics of the LED and the dimmer, so its best to check things out before committing to specific hardware.
James King says:
There is a huge variation in retrofit lamp designs, their dimmability and compatibility with dimming systems. While a small quantity of lamps may work on a basic dimmer, the characteristics of the lamp may cause problems when putting larger quantities on a circuit, so it is important to check the details.
Questions need to be asked of the lamp supplier and manufacturer; is the lamp dimmable by leading-edge or trailing-edge controlled mains, or both? If you get a blank look or silence on the phone, then beware! The compatibility issue has been around long enough for lamp manufacturers and suppliers to know what that question means.
If a lamp is said to be dimmable by either format then, in our opinion, it should perform just as well under both formats. If it performs better when controlled by leading-edge or trailing-edge then it should only be sold for the most appropriate dimming technology.
Regardless of the dimming format, the performance of the lamp is also key. While a poor dimming curve can be masked by scene setting, instability and flicker in the lamp when dimming can only be resolved by good quality circuit design within the lamps.
Over recent years the performance of lamps, particularly the popular LED filament type has got significantly better and we have seen mains dimmable lamps dim very well to very low levels. And as the new generation of retrofit dim-to-warm lamps expand we hope to see a more natural, tungsten like colour shift on offer.
0-10v / 1-10v Dimming
Another form of analogue dimming, this system was first designed for dimming fluorescent loads. Rather than reduced the voltage into the lamp, this requires a separate signal that ‘tells’ the control gear / driver what output is required; with 0v or 1v being the lowest output and 10v being maximum light output. It’s a convenient way of dimming LEDs in small commercial projects and larger residential projects.
Because its an analog system, you need a 2-core signal cable for each lighting channel, so that can be an expensive over-cost in installation costs. There are practical limits to the length of the signal cables, which need to be screened from any interference from 240v mains cables, so the apparent convenience of running mains and signal cables side-by-side is to be avoided.
James King says:
Unfortunately, the proliferation of low cost 0-10v and 1-10v controlled drivers – and an obsession with cramming in multiple control formats into a single driver, has muddied the waters somewhat.
Traditionally 0-10v was used for old-school control desks where 0v = zero output and 10v = maximum output. This often required the controller to output a current to drive the dimmer or driver. If the signal was broken the lights would go off.
1-10v works slightly differently, where the driver or ballast generates a 10v signal which is then “pulled” down to a low level by a controller. 1v is typically the minimum level the drivers could be pulled down to, which equated to minimum level. If the signal was broken the lights would revert to full brightness.
10 years ago we saw a dramatic drop in demand for 1-10v control but with the introduction of low cost LED Drivers. This has since reversed and with LED Drivers we now see a complete mix of analogue dimming technologies. Some require a current to be sourced from the controller, some want it sunk; some work well on standalone rotaries but don’t work with full control systems, some work well with only a couple of drivers linked on a circuit, others go haywire if connected in multiples. We have seen drivers and power supplies induce instability in their own 1-10v control lines, which the causes issues with minimum brightness and pulsing / flicker.
We have even found that some “multi-function” drivers (0/1-10v, push dim etc) even need an additional component added in at the driver if they are being connected to a control system or in multiples. Did we get the blame for the lights not dimming? Of course, we’re the controls manufacturer, it must be our fault … Did we get that solution handily presented to us by the UK/European source? No … Did the off-shore supplier let us know? No … After trawling through hundreds of pages of the off-shore OEM’s website we found that … (let me know if I am sounding bitter….)
On a more positive note, many of the established manufacturers have some very good 1-10v controlled drivers and have obviously spent time (and money) on bringing out good quality, reliable kit.
DALI Dimming
DALI is probably the most popular dimming protocol for architectural projects. DALI stands for Digital Addressable Lighting Interface, and the clue to its success lies in that word ‘digital’. A single DALI controller can provide separate control instructions for up to 64 fixtures.
And because it is a digital technology, information can flow in both directions, from the controller to the fixture and back from the fixture to the controller, so its possible to monitor the ‘health’ of the light fixture – a boon in these ‘smart’ times.
DALI signal wiring can be done using conventional mains voltage 2-core electrical cables and there is no problem with potential interference from neighbouring mains cables.
James King says:
DALI can simultaneously be a blessing and a curse when it comes to delivering a project. The wiring is wonderfully simple which makes it ideal for heritage projects or external lighting applications where cabling needs to be kept to a minimum. It offers a very useful solution for reasons of visual impact, limited access or cost of the cable and labour. It is also great for applications where the space is yet to be leased, enabling tenants to come in post-build and decide how space is to be laid out and the lighting controlled. The two-way communication to drivers is also useful for fault reporting or Emergency Testing where required.
It has to be said that, where lighting designs have already defined the control groups and the two-way reporting is not required, the flexibility of addressing fittings by DALI can become a drag when scene setting which can eat up programming time (the fittings may be connected but they need to be addressed before the scene setting can begin).
Using DALI drivers in a basic DALI Broadcast format where the wiring is more akin to 1-10v with individual control cables for each group of lights, can be a good trade-off between what is available from the lighting manufacturers and what is needed for a particular project. Many manufacturers have been able to dramatically reduce their inventory by only offering DALI drivers.
And bear in mind that using drivers in a DALI broadcast format may remove the need for addressing individual fixtures, but it does require individual control group wiring. So while it works for some applications it doesn’t work for others.
DMX Dimming
Digital Multiplex was conceived for theatrical installations, which calls for a large number of lighting channels with a very quick light response. A single DMX universe can control up to 512 channels.
DMX hasn’t been popular in architectural projects unless there is a specialist feature, such as colour changing or dynamic light art requiring many channels and swift scene changes. But this situation is changing as designers appreciate the aesthetic uses of the LED; the boundary between ‘commercial’ and performance’ is blurring and we’re seeing ‘DMX companies’ expanding into architectural lighting.
DMX signal typically wire uses a shielded 3-pin XLR cable, although RJ45 CAT5E cables are also common with either method being daisy-chained around each DMX device.
James King says:
Our most common application for DMX is straight forward colour changing or tuneable-white control in Architectural applications where the drivers and LED sources are readily available and dynamic control for sequences and smooth fades are easily achieved with DMX.
DMX control is also capable of reaching much further than simple channel controls with multi-universe, pixel-based control being possible and blurring the boundaries between lighting and video technologies.
And a footnote from James …
We could probably argue until the end of time (or at least until last orders..) over whether DALI is the most popular protocol or not. For commercial projects it is almost entirely DALI-based control, though architectural projects still tend to see a mix of protocols.
With all of the lighting protocols and technologies there is an increasing need for manufacturers and designers to talk openly and honestly about what each project requires. Which protocols will deliver the right type of control whilst also considering the impact on installation and maintenance costs? In very simple terms some lighting protocols are better suited to some applications and some have rather particular requirements when considering the wiring or programming. By getting more involved in the design process we can hopefully make the engineering side of a lighting design a little easier for everyone from, initial design to final delivery.