LED lighting in the home is becoming more popular due to the energy and money saving benefits it offers over traditional halogen lighting. One of the most common problems that an electrician faces when installing LED’s is enabling them to dim.
Resistive dimming has become a standard way of dimming halogen lighting and it works by reducing the voltage allowed to the bulb with a variable resistor.
A resistive dimmer switch is easy to install because it is simply wired between the mains (240V) power and the bulb, however whilst the lighting is dimmed the voltage resistance is converted to heat and is not considered energy efficient.
Note: LED’s cannot be dimmed using resistive dimming; it will slowly damage the LED’s.
Pulse-Width Modulation Dimming
Pulse-width modulation works by switching the voltage on and off at a variable speed. This causes a flickering effect that is too quick for the human eye to see. By increasing and decreasing the switching speed it increases and decreases the max possible light output and dims the LED.
A problem found with PWM dimming is as the amount of dimming increases so does the amount of time the voltage is turned off. This will eventually fall within the flickering speed in which the human eye can see.
This flickering can normally be seen when the LED is dimmed to below 10% of its original light output.
A TRIAC (Triode for Alternating Current) dimmer works by conducting the current in both directions, alternating at a variable speed. This makes the switching much faster than Pulse-width modulation dimming so it never goes within the flickering speed of the human eye.
Both PWM and TRIAC dimmer modules require a signal to tell the dimmer how much to dim the LED’s. The current standard is 0-10V.
0-10V signals work by sending a separate 10v signal to the PWM/TRIAC dimmer module and then using a resistive dimmer to reduce the voltage on the 10V signal. As the voltage drops the dimmer module reduces the brightness on the LED’s in relation to the voltage.
10V = Dim at 100%
8V = Dim at 80%
3V =Dim at 30%
DALI is an open source 2 way protocol designed for controlling lighting in the home. It is a royalty free standard meaning it is possible to mix and match DALI module’s from different manufactures. DALI works by assigning zones and linking all the DALI modules for each zone together.
The DALI controller can then control multiple zones individually.
The DMX 512 protocol was originally designed to control nightclub and theatre lighting and has only recently started to be used in the home.
This means that each dimmer module is given a DMX address so it knows which channel to read and adjust the brightness accordingly. Each dimmer module has a DMX In and DMX out socket so the data signal can be daisy chained from one module to next.
DMX can control colour changing lighting as well as non-lighting devices. E.G. Fog machines, Blinds and even motorised doors.
Just a note about the triac waveform above: a triac conducts from the trigger point until the end of the half cycle. Only with an IGBT can you turn off in mid-cycle.
which driver should be used to drive LED by using pic16f877a?
It has been a massive problem up till now but there is a new dimmer on the market with totally different technology, it is a silent software dimmer, the grid version does 5 – 250 watts with any lamp & zero flicker. The dimming range is much better too. It’s nominated for the Lighting Design Awards, but you can check it out here : http://www.zanocontrols.co.uk of search ZGRIDLED
I have some LED lamps 10 watt is 10led 1 watt in series in my led down light. in my flat, Pwm dimming0 to 10v required. Could anybody give advice about which ic is best for ac dc application Many Thanks in advance.
we are needed circut digram for dim and speed coktrol of motor
I think the broken LED current by two problems:
They need a resistor in parallel with each diode a little, that will balance one generates a polarization + A K-defined.
This is only for ohmic region polarize PN, about 1 to 4 microA.
For example, AK 10Kohm.
In many columns of light that we can buy such cheap solution is not available.
I’ve fixed many of the problems typical of random fusion serial devices using this method.
The PWM lighting gives them a break cyclical, which cools the junction and in return receive a longer life.
also after the break, improved device performance because a saturated heat on junction zone of a led LED, generates more light for the same power consumption, only in the starter time, that its repeated in each time.
Enjoy the LED light, but I think its laser component is to blame for my problems of permanent spots in my vision
I received the comment from one of EEP’s readers. I would appreciate if you could reply on his comment.
Here it is:
Generally: Many LED devices (not the LEDs themselves, but the full combination of LEDs, power socket and internal control circuitry) are NOT suitable for dimming. Most often, the internal circuit operates by sending pulses of predefined current amplitude through the light-emitting elements, and only a minority (the costlier ones) of those a suitable for dimming without causing inconvenience for the user, and/or damage to the unit itself.
1) A resistive dimmer switch:
This is not a switch as such, but a potentiometer, or regulator, for the ones who may not know what a potentiometer is.
2) Using a resistive dimmer between the main voltage and the transformer will damage the transformer:
A transformer will not be damaged by having a resistor in series with its primary winding, but possibly a low-voltage (switching) power supply might.
3) LED’s cannot be dimmed using resistive dimming; it will slowly damage the LED’s:
The main LED elements ARE controlled by limiting the current through, and will in many cases controlled by resistive limiting. In some cases, though, the LED element itself can be made to shine apparently brighter, by pulsing higher than average currents through the elements. This is mainly because the eye is sensitive to the peak light level, rather than the average level.
4) Pulse-width modulation works by switching the voltage on and off at a variable speed.:
Not necessarily. The term means that the source is on for a variable proportion of each cycle, while the frequency might well stay constant. Your diagram looks correct.
5) PWM – flickering:
Is more likely caused by the time the power is on becoming so short, that the internal regulation circuitry does not have “time” to “turn on” the light.
6) TRIAC Dimming:
The TRIAC is only able to switch off when the current passes through zero. (As opposed to IGBTs).
I have no comments to the remainder, as I have not studied any of that nature in the past.
Good answer. the original text is incorrect
I have some LED lamps in my flat, but I had bumped with such problem as “blinking” when tumblers are off. Could anybody give advice about? Many Thanks in advance.