3-way dimmer switch replacement

[sjchapman]

First quote (from a sparky in the next road) to fit the switch If I get parts is £30

 

[ban-all-sheds]

Or by a controller designed to work with a PWM driver.

A PWM driver controlling current through the LED element requires adequate smoothing of the pulses of current into smooth into the average current. If the smoothing is in-adequate then the brightness of the LED will vary rapidly at the PWM frequency. There will be pulses of bright light separated by periods of dark.

The eye does not smooth the light but retain the peak brightness so the LED will appear to be brighter than it it should appear.

I think you will find that PWM does actually work.

I think you will find that if the frequency is in the 100's of Hz people do not detect any flickering. As for perceived brightness - so what? The user turns the knob until the level he perceives is what he wants to perceive. If that is different to what it "should" be given the duty cycle then I am at a total loss as to understand why that matters.

I think you will find that if you try to dim LEDs by controlling how much current flows through them that you will have a limited range and a noticeable problem with the colour changing.

 

[bernardgreen]

I think you will find that if you try to dim LEDs by controlling how much current flows through them that you will have a limited range and a noticeable problem with the colour changing.

Controlling the current gives perfect control until the current is extremely small.

In the majority of single colour LED elements the visible light is produced by a phospher layer acitivated by UV produced by other layers in the LED element. Hence colour change is not going to happen as it is the phopher that determines the colour and not the amount of UV produced.

A "version" of PWM is used to make LEDs look brighter while reduce the power used. Many warning lamps at road works pulse the LED element with a current 5 times the normal current for leass than 1 /20 of the time. Hence average current is 1/4 of the normal current the LED requires. The pulse creates a very bright pulse which the human eye retains until the next pulse. Obviously theelement has to be able to cope with the 5 times current pulse which most can, early LEDs could be run with pulses of 10 times normal