LEDs, despite their inherent benefits, can be incredibly frustrating. Lighting designer Sue Stokes explains.

One thing you learn as you go along is that gaining wisdom in any area of life can be a painful process.

Sometimes in the field of electrical installation, earning that wisdom comes with a bolt. As one anonymous philosopher with a sense of humour put it, “Experience is the comb we receive after we’ve lost our hair.”

Well if you’ve done any work involving wiring LED lights lately, chances are you’ve gained some hair-loss-worthy experience… in the form of blowing them up.

Most people by now are familiar with the energy saving aspects of LED lamps. With a neat, compact size and options for retrofitting low voltage downlights, LEDs have emerged as the alternative of choice to halogen lamps in order to achieve a BASIX compliant (or energy efficient) residential lighting solution.

If only that was the end of the story, then life would be so much simpler.

In addition to differences in quantity of light output and colour rendition, the wiring and control aspects of LED lights is very different to their low voltage halogen counterparts.

For residential installations, as far as a true one-to-one replacement of halogen lamps, LED technology still has some way to go.

In contrast, light output performance of halogen lamps is predictable, they are simple to wire and very easy to dim.

Initial costs with halogen fittings are relatively low and if the lighting design is appropriate, it’s a comfortable source to live with.

When it comes to LED lamps however, not all bulbs are created equal.

In the range of LEDs there are constant voltage, constant current – 350mA and 700mA, various colour temperatures and life expectancies across the board; Seoul LEDs, Cree LEDs, SMD LEDs and COB LEDs, just to name a few. Some LEDs work when wired in series, some in parallel. Then you need to ensure you have the correct driver specific to the particular fitting and circuit load being installed.

Just when you think that all sounds complicated enough, then comes that question: “Can I dim them?”

Philips Dynalite and Clipsal C-Bus both have control units capable of dimming both constant current and constant voltage LED lighting. But it’s not always as straightforward as dimming incandescent fittings and can often be quite a bit more expensive to achieve. While I have to question the importance of dimming a 1W LED light fitting, in residential lighting installations most people do want the option of dimming at least the overhead lighting. Where an automation system is specified, dimming of LEDs often may require another level of control gear in addition to the LED drivers.

The difference in dimming LEDs is due the process of generating light being totally different to that of incandescence or fluorescence. It is process called ‘injection electroluminescence’. It is a result purely of the atomic differences within the LED die and is much more highly efficient in producing light than almost any other light source. In addition to differences in quantity of light output and colour rendition, the wiring and control aspects of LED lights is very different to their low voltage halogen counterparts.

There are two sets of dopants in the LED die which form distinct layers and it’s the junction or boundary of these where the electroluminescence occurs. Unfortunately, not all of the light produced at the junction is released from the die. Some light is re-absorbed and is converted to heat, gives rise to that huge heat sink you see on the back of some LED lamps. The quality of the junction and the heat dissipation from it is a determining factor in the life of the LED.

Light that is generated this way is basically a single wavelength of colour, so to convert that to white light a phosphor coating is used to cover a blue LED die. The die stimulates the yellowish phosphor and different proportions of the two can be combined to produce light in a range of colour temperatures.

Residentially, warm colour temperatures (in the range of 2,700K to 3,000K) approximating incandescent lamps are preferred. A colour temperature of 4,200K is the preference in offi ce installations as the cooler temperature has been proven to enhance productivity. Used residentially, a colour temperature of 4,200K would probably be experienced by the home owner as glary and lacking in atmosphere.

Interestingly, once in operation, LEDs don’t suffer catastrophic failures. That is, rather than the lamp failing suddenly as a traditional incandescent or fluorescent lamp might, they tend to just loose light output slowly over time.

The common reason for sudden failure at installation of LEDs is due to wiring incorrectly or using the incorrect size driver. The driver, which steps the 240V AC current down to either 12V or 24V, also converts the current to DC. With LED drivers, it is not only the value of the minimum wattage that should be correct for the circuit, the maximum wattage also needs to be within range. If you connect a circuit of LED lights to a driver with a too high wattage you risk blowing the fittings. Connect to a driver that is below the wattage of the circuit and the driver will prematurely fail.

When it comes to LED lights it is imperative to follow manufacturer’s instructions with regard to their wiring and supply of the appropriate driver. Or, as many of us have already discovered, the 50,000 hour rated life of an LED fitting can quickly turn into zero hours.

Controlling and dimming these fi ttings on an automation system can seem like a mad science of its own. The automation specialist on the team in liaison with the lighting manufacturer should be able to provide advice and guidance on that aspect of the installation.

So if you are lucky enough to still have hair, don’t tear it out just yet. In the area of LED lighting technology there is on-going development and LEDs are constantly improving, as are the ways to control them.