Dimmable LED Light Bulbs - Uses, Advantages and Applications
Dimmable LED light bulbs are important for applications where variable light levels are required such as when giving an office presentation with a projector or relaxing in your lounge room watching TV or sipping wine versus reading a book or playing a board game. Similarly bedroom LED lighting is typically dimmed prior to bed but can be made brighter when getting ready to go out or early in the morning. Having the right colour light such as a bright natural or cool white can even help you to wake up in the morning and is even used to treat sleep disorders particularly relating to shift work. In countries where there is lack of day light between October to March, a day light (natural white) colour can be used to compensate for the lack of light and potentially prevent the occurence of light related disorders such as Seasonal Affective Disorder (SAD)
Depending on the situation and activity you may need to adjust the LED light level to a more comfortable or more optimal level rather than having your light bright all the time. Another advantage of dimmable light bulbs is energy savings. When an LED light bulb is dimmed the current is reduced and therefore the power consumption resulting in a further saving in electricity.
How are LED Light bulbs Dimmable
As mentioned in our section on the history of LED lighting scientists found that in 1951 the amount of light produced was proportional to the current as the current (electricity or electrons) is converted into light (photons). This means that a doubling of the current leads to a doubling in the brightness of the light in lux or lumens.
Therefore, LED lights can be dimmed by reducing the current either with continuous or linear dimming or through pulse width modulation (PWM) dimming which involves turning the LED on-off at a very high frequency. Both techniques are found to work very well although PWM dimming can be more unstable.
Dimmable LED Lights - Problems with LED Flicker
Pulse Width Modulation (PWM) or Linear LED Dimming.
However, dimming it is not as simple as reducing current given the current supplied by the electricity companies is alternating current (AC) and the various manufacturer’s dimmers use a form of PWM or phase control dimming to essentially chop the voltage signal at the input of the traditional incandescent light bulb or LED driver. The traditional incandescent light bulb which function as an integrators of AC currents will quite happily smoothing this signal without leading to flicker. However, this can cause some problems with LED lighting in the form of flicker due to the input current to the LED bulb being too bumpy or variable.
Dimming Inrush Currents at LED Driver Input.
The other problem is the so-called inrush currents or repetitivepeak voltage/current to the LED driver or other power supply where the input voltage to the driver rises rapidly part way through the AC line cycle (every half-cycle). This occurs due to the interaction of the PWM output of the dimmer and generally the capacitive inrush currents of the LED driver. The voltage spike causes ringing on each half cycle of the AC wave form which can also show up as flicker and/or lead to premature failure of the dimmer and/or LED driver. Therefore, in all commercial installations and some residential or where ever dimming is frequently used such driver inrush currents on dimming should be measured to prevent premature failure of the lighting system and/or excessive flicker and to ascertain the maximum number of LED lamps that can be safely attached to the dimmer. See our:
DynaliteCompatibleDimmer/Dimmable LED Driver
DynaliteCompatibleDimmer/Dimmable LED Driver(Power Supply) for further information which we have tested for flicker and inrush currents/voltage spikes on the majority of Leading and Trailing Edge Dynalite Dimming Modules.
Fortunately, electronics can be used to smooth out the current for the LED leading to a LED light bulb that is dimmable to some extent. Although this usually comes with an additional cost of special circuitry for driving the LED bulb. Hence, if you require a dimmable LED light bulb you must make sure you select one that is labelled as dimmable. Some LED bulbs will also have a better dimmable performance than others, some will typically flicker as they are dimmed which is not acceptable.
Dimmer Load Incompatibilities.
The other factor which can result in poor dimming performance is insufficient load from the LED light globe. This is due to the Dimmers being designed for at least a 35W or 50W globe, so a 10W globe can sometimes be insufficient to properly switch on the dimming circuit. In such cases we recommend using a Clipsal CFL low voltage dimmer or adding at least two LED light bulbs to your dimmer circuit or using a load correction device.
Dimmable LED Lights and DimmerCompatibility
At Lite On LED we thoroughly test our dimmable LED light bulbs to ascertain their performance on various dimmers. The findings of our test can be found in the products description under "dimmer compatibility". Typically dimmable LED bulbs either have an external driver which is dimmable (usually in commercial applications) or have an internal driver that is dimmable and runs on 240V AC. The latter is typically the Edison E27, B22 or GU10 type LED light bulbs. There are few LED MR16/GU5.3 LED bulbs that are reliably dimmable. The Philips Master MR16 10W is probably the most famous dimmable MR16 but even this bulb is only dimmable on a selective list of 12V AC electronic transformers (as listed by Philips) and dimmers and may well not be dimmable on your existing transformer or dimmers at home. So be weary of retailers claiming dimmable MR16 LED light bulbs.
Most dimmable lights work well for most of the time but as discussed further below there are certain situations where they will occasionallyflicker. If this is unacceptable, you need to ensure you purchase a 100% flicker free dimmable LED bulb.
Our approach at Lite On LED is to also use the E27/B22 or GU10 dimmable light bulbs which are very reliably dimmable without having to worry about existing transformer compatibility given they all run on 240V AC. For those of you at home who still have MR16 electronic transformers and sockets we have a relatively economical upgrade option where you can purchase the dimmable GU10 LED bulb and the GU10 socket with mains plug. Alternatively, you can purchase our commercial MR16 light bulbs with dimmable external driver and plug in mains socket for a few dollars more.
A further note is that few LED light bulbs will dim to 0% or even 10%, however this is not generally an issue as most users will want to dim the brightness of the LED light bulb but maintain useable light levels rather than creating a somewhat dark atmosphere. If you require dimming down to 0% or 5% we do have some special “fully” dimmable LED light bulbs. Another way to achieve lower light levels is to select a dimmable light bulb with a lower wattage to start with, say a 7W dimmable instead of a 10W dimmable. For example, a higher wattage LED light bulb will typically not be able to be dimmed to the lower levers of a lower wattage LED light bulb.
Dimmable LED Lights and Power Supply or Mains Fluctuations/Variability
LED Lighting Dimming and Electrical Interference.
A final issue with LED lighting is the quality of the supply voltage from the electricity company with relates to electrical harmonics and the stability of the power supply to your home or business. Power quality or mains interference relates to short term transients as well as continuous state distortions leading to variations in the sinusoidal AC waveform. The problem can be caused by a number of issues including nearby machinery, solar flares or poor power quality management at the supplier. Another phenomenon can occur late in the evenings when households begin switching off their electrical devices such as air-conditioners, lights and televisions leading to a sudden drop in the demand for electricity. This can lead to instability in the electrical grid/supply as it is slow to compensate for the sudden drop in demand resulting in typically a slight increase or spiking in mains supply.
LED Lighting Dimmingand Interference from Zellweger Ripple Tones.
A further problem has been the introduction of Off-Peak power tariffs orZellweger off-peak tones or ripple control signal which is an electrical switching device used to switch off-peak electrical loads, such as off-peak hot water, on and off or “smart” electrical meters. To do this power stations transmit a ripple on the mains transmission lines often around 10pm when off-peak rates start. The ripple noise is picked up by the Zellweger which adjusts the smart meter to charge a different tariff. This noise can cause problems with electrical devices, particularly dimming circuits and LED lighting when lights are often dimmed in the evenings. Parts of NSW and QLD are most commonly affected.
LED Lighting Dimmingand Mains Voltage Fluctuations.
In the short of it, these power fluctuations can sometimes cause instabilities in the dimmer circuitry causing your dimmable LED globe to flicker, albeit for a relatively brief time. Our tests have shown that these mains power fluctuations and dimmer instabilities even effect normal incandescent light bulbs so the problem is not always unique to LEDs. However, often resetting the dimmer by turning it up and then back down is enough to eliminate the flicker, or reducing the dimming such that the LED driver has sufficient range to sufficiently smooth out the excessive voltage fluctuations. In this regard even the best dimmable LED lights will flicker occasionally for a brief period, although usually this is not a great impediment given the low frequency of occurrence and short duration. If flickering becomes bothersome there is the option of having your electrician install one of our single phase AC mains line filters or voltage optimisers/power conditioners which is installed before the dimming circuitry. This filter will act to smooth out any unwanted voltage fluctuations and resultant flicker. For LED light bulbs with external drivers we also offer a voltage smoothing device which is connected between the LED light bulb and the LED driver which can further eliminate the majority of any potential flicker.
LED Lighting Dimming with DALI, 0/1-10V, DSI and C-bus LED control systems.
The other option as mentioned elsewhere is to use DALI, 0/1-10V, DSI and C-bus LED dimming control systems which are independent from mains voltage fluctuations.
References:
Understanding Power & Power Quality Measurements. AEMC Instruments.
Power Quality. A guide to voltage fluctuation and light flicker. BC hydro Power Smart.
Technical Note: Repetitive peak and inrush currents. Alliance for Solid-State Illumination Systems and Technologies. March 2011.
Controlling LEDs. Technical White Paper. Lutron. Jan 2011.
Solid State Lighting for Incandescent Replacement—Best Practices for Dimming.A NEMA Lighting Systems Division Document. 2010.
