The Application of Dimmable LED Spots and Bulbs
Among the issues of LED lights dimmability is one of the latest challenges still yet to be fully solved. Dimming LEDs is theoretically easy, because analogue dimming, that is the adjustment of current, has long been an option. However, this method only works safely when used with one LED bulb. Systems of LEDs require a more sophisticated method of dimming. The two basic forms of dimming are the PWM or Pulse-Width-Modulation and the analogue dimming, both of which are switched-mode regulators. These two types are similar in the sense that they both control the time-averaged current through the diode.
Analogue dimming is a very simple way of dimming, it is the adjustment of cycle-by-cycle of the LED current regulated with a potentiometer. The MOSFETs is adjusted to the LED increasing and decreasing its intensity.
The disadvantage of analogue dimming is that it only works safe as long as we dim a single light bulb. Systems of LED lights require a more refined technique. The difficulty of dimming a system of LED lights is that there are many types of LEDs, requiring different methods for dimming. If there is a system of lights we would like to dim, the various LEDs may react diversely to the same amount of current, and as the current is reduced some LEDs can turn off later or sooner than others. Also, analogue dimming largely changes the colour of the light, similarly to when it is used with incandescent lights.
The most frequently used technique of dimming LEDs is Pulse-Width Modulation, which is basically the cutting of the phase at a certain frequency. PWM switches the devices between fully on and fully off at a frequency that cannot be told by the human eye, therefore LED bulbs always run on the forward current recommended. The frequency of switching determines the brightness of light, so the longer the lights are “on” the brighter the light will be. This is the same technique used in incandescent light dimmers as well, except that incandescent lights react to current more slowly, and therefore require a different frequency.
Two types of Pulse-With Modulation signals are used often with dimming light: the leading-edge and the trailing edge techniques. These two are different ways of cutting the phase, and result in separate dimming technologies. The most frequently used dimmers of LEDs use solely the leading-edge technology. Dimmers marked as R or RL are suitable for most dimmable LEDs, since they work with the leading edge technology and do not include electronic transformers. TRIAC drivers, or devices governed by the DMX and digital addressable lighting interface (DALI) protocols and, in the future, may include wireless (RF) as a control option, that is dimmers that turn or slide with a knob, all work with dimmable LEDs.
Alas leading edge technologies controlled with a touch or push button, are often powered by an electric transformer, excluding many dimmable LEDs.
The other type of phase-cutting technique is trailing edge technique, usually used in MOSFETs or is not suitable for the majority of dimmable LEDs. One of the latest inventions appearing on the market is the RAIS lamp technology. RAIS lamps offer a higher degree of functionality and seem to work with all types of dimmers available on the market. However RAIS technology is still new, and its long-term effect on LEDs have not been fully tested. If they prove to be trustworthy their application both domestically and commercially, can turn out to be much safer and easier than previous dimmable LED lights’.
In the ever-evolving technologies of LED lights, dimmable LEDs are still to be developed to further compatibility and better performance. Since there is no general rule for what dimmer your LED might be suitable for, always check the technical details with the distributor. Application of LED lights with non-compatible dimmers might ruin the LEDs, and they are, at the moment, not the cheapest solution of lighting.