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New Light Fitting, bulb stays on but switch is off??

Postby Umy786 » Sun Jan 18, 2015 11:54 am

Hi everyone

I've replaced the bedroom light from a pendant which had a Phillips energy saver to a 3 candle LED bulb fixture which is connected to a LightwaveRF dimmer.

Before the change everything worked fine, I wired the fixture as the previous pendant was but as soon as inserted the bulb it came on, even though the switch is powered off.

I did have my home re-wired around a year or so ago so the wiring is all new but I can't for the life of me understand what's causing this problem and it's extremely annoying.

I'd appreciate any help or advice anyone could offer.

Can post pics if required.

Many thanks
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Postby ericmark » Tue Jan 20, 2015 9:13 am

There are three possible faults.
1) Inductive or capacitive coupling taking enough energy to light LED's.
2) Connected to permanent line not switched line.
3) Gone below the minimum wattage the dimmer is designed for.

The Lightwave RF dimmer uses 0.5W and warns there may be problems if the lamps used are under 10W the minimum is 3W that is when the bulb is dimmed so really does need 10W bulbs in total as a minimum.

It also states the switch may need configuring for low wattage bulbs.

Plus also states you must use compatible bulbs.

The frequency stated is 433.92 Mhz which is shared with radio amateurs who are the primary users you are using milliwatts they can use 400W clearly any local ham can swamp your system.

A LED works on around 3V and any 230vac bulb must have some sort of control gear built in. The standard way is to use a switched mode power supply inside the bulb which will auto compensate for any voltage variation typically 150 - 250 volt. In order to dim the power supply has to read the information sent from the dimmer and it sees a clipped wave form as an instruction it may read the leading or lagging edge of the wave form or both.

The dimming switch may also be leading or lagging and with both LED and transformer driven lamps one has to be careful that the two units match. I think this matching is likely the problem.

I would try fitting tungsten bulbs to verify it is the matching dimmer to bulb and then if re-programming the dimmer does not work buy bulbs which are recommended my dimmer manufacturer.

I have removed all my dimmer switches because of the problems getting compatible LED bulbs. I found bulbs cost 3 times the price to be dim-able and also tend to have a shorter life. Since the colour stays the same when dimmed there is not the ambiance of the tungsten bulb so having table lamps, standard lamps and wall lamps to vary the lighting or as many hotter countries do having main lights split 1/3 and 2/3rds with two switches giving three levels of lighting is a better system than dimming the lights.

With lighting for a room now being around 10 - 30W the 0.5W used by the switch seems quite a lot. Also since dimming switches never switch completely off in theroy to change a bulb the power needs switching off at the consumer unit. This is not what I want to do.
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