One of the most popularly-cited disadvantages of LED lamps in the past has been that you can’t dim them. Dimming an LED lamp is a very important thing to do, too, since adjusting the light intensity makes it actually comfortable.
An LED is not a pure resistive load, so these lamps have problems with dimmer switches – particularly older switches. It is such a problem, in fact, that it might actually be a concern to those with photosensitive epilepsy.
In 2010, researchers found that pairing an LED lamp with a typical residential dimmer switch caused the light to flicker 3.15 times per second (3.15 Hz), which is a frequency known to trigger a biological response.
But since LEDs are “the future” of the lighting industry, there’s a clear need to make them work as well as their incandescent ancestors. So how can we combat this? There are LED dimmers on the market, which are just a specialised type of LED driver.
An LED driver regulates the power to an LED device or a string of LEDs, supplying a constant amount. The LED’s energy needs are always changing due to temperature fluctuations, and they may get too hot without the proper driver.
Constant Voltage Drivers
LEDs with a supply current of 20-70 mA need this. These are the 0.1-0.3 watt devices, the “signal LEDs.” The little red light in the remote control.
Constant Current Drivers
LEDs with a supply current of >100 mA (typically 250 mA, 700 mA, 1A, 1.5A) need a constant voltage driver. They require a constant current, and must be connected in series.
These are the 1W, 3W, 4W, 6W lights used in backlit information signs, large HD LED displays, and so on. Using the right constant current driver can increase the already substantial lifespan of the LED light.
Typical residential dimmers switch ON/OFF about 120 times a second (i.e. 120 Hz). This cuts off a portion of the AC power cycle (a process known as phase control) and so regulates the amount of power going to the filament.
This reduces the intensity of the light it gives out.
Because of how AC power works, there’s always a small flicker as the power cuts out once per cycle. Most people can’t perceive this (only about 1% can, according to some figures), so it seems as though the light is constantly ON.
Ideally, the dimming flicker should be imperceptible: if the frequency of the ON/OFF cycle is fast enough, most people won’t be able to see it. The threshold is at around TK Hz.
Constant Current dimming is an effective way of dimming LEDs. This method changes the current being supplied to the LED, and it’s good for all LED lights, although dimming might change the colour output of older diodes.
Where Can You Find These Devices?
With the right LED driver, it is more than possible to safely and comfortably dim these extremely energy-conscious light fittings.
There are a few LED drivers in the Sparks Direct store that are more than capable of dimming LED lights for various applications.
As well as those two, there are many more in our LED lighting section.
Resources & Links
- David Cooper argues the case for dimmer compatibility in LEDs Magazine .
- A much more technical explanation of the compatibility issues.
- Another link to the study which demonstrated a cause for concern for photosensitive epilepsy.
- A tip of the hat should go to Jon Excell at The Engineer for leading us to that study.