In this article the experts at Zano Controls examine why your LED installation won’t dim and what you might need to do about it.
The ﬁrst problem is one that Zano Controls has mentioned before, but bears repeating. Analog dimmers simply can’t control LED eﬀectively. You might manage to achieve a limited dimming range with a TRIAC model, but it’ll never be fully eﬀective, resulting in ﬂicker and buzz.
Why don’t they work? In a nutshell, old fashioned TRIAC dimmers operate a current interruption method to dim light output. If you strip back an analog and a digital dimmer you can see the coil that physically disrupts the current between the switch and the lamp it’s connected to.
For lamps that run on a continuous forward current, like an LED driver, this interruption can actually be seen in the lamp’s light output. You can also hear the coil buzzing when the controls are set to uncomfortably low levels.
Digital dimmers replace the coil with a circuit board. No coil, no problem. Well, almost! Unfortunately not all of your LED dimming woes can be solved by switching to a digital dimmer.
Mislabelling on LED lamps
Despite huge advances in LED technology – and a signiﬁcant move away from cheap and cheerful lamps – there is still a problem with wattage mislabelling. Sometimes, there can be a huge disparity between the actual wattage of an LED lamp and the wattage printed on the box. While a lamp may only use 12W once it’s up and running, it could take a lot more than that to get started, thanks to the driver’s initial
boost to bring the lamp to full brightness.
The moment the lamp is switched on, that driver causes an ‘inrush’ current – a surge of power that can peak at more than double the wattage advertised on the packaging. A 12W lamp, for instance, could reach 30W for that brief ‘powering up’ period. Fit 15 of those lamps, plus a dimmer, to a single circuit and you’ll overload your dimmer.
Fortunately, you don’t need to discover that the hard way. At Zano, we can test the number of lamps you need per circuit to make sure that the wattage is compatible with the controls you want to use.
At the opposite end of the scale we have low loads: equally as frustrating to contractors, but simple to ﬁx with the right dimmer. LEDs – inrush current aside – operate at a much lower wattage than traditional incandescent lamps. A single warm white LED may be around 4-5W, which is ﬁne for your average 10-300W dimmer if you have a few of those lamps on a circuit. Try to install dimming controls on a circuit with a combined wattage of less than that, however, and you start to encounter problems.
Take an en-suite bathroom, a small bedroom or even a reading nook (very Highbury & Islington). Say you have space for just two downlights, and each lamp is 4.5W each. A minimum 10W controller won’t
support that low level, resulting in ﬂicker and drop out.
The same problem occurs when the total wattage of a circuit at full brightness exceeds the minimum wattage of the dimmer, but drops beneath that limit when dimmed to lowest levels.
Every Zano dimmer is built with a minimum level preset function that allows electricians to set the dimmer’s lowest level above that ‘drop out zone’, eradicating ﬂicker and drop out.