DIY Doctor

Issue with kitchen lighting changing from halogens to led on dimmer switch

Postby Clouseau » Sat Jan 09, 2016 10:26 am

Hi, I’m new to the forum so please bear with me.

My kitchen has 12 x spotlight fittings in the ceiling on a dimmer switch. I have been gradually replacing the halogen bulbs with LED lights. Until today, I had 6 x LEDs (the box says 5.2w as bright as 50w halogen) with 6 x halogen remaining. It was working fine until another of the 6x halogens went and so I thought I’d get the whole lot changed then went out today and bought another 6 x LEDs. I’ve replaced 5 of them and have now noticed a couple of problems. I do not know what the specifications are for the dimmer switch.

1) When the lights are up full they’re flickering and there’s a buzzing sound coming from the switch. The flickering stops and the buzzing reduces more the dimmer they are. If I have them on their dimmest after a while they all flash on and off repeatedly. I’m guessing I will have to get a new dimmer to accommodate the combined wattage of the individual bulbs? Does that sound right and if so, what can anyone recommend for the bulbs I’ve described above?
2) The reason I’ve only replaced 5 of them is that the one that seemed to have gone didn’t come out completely. The 2 x small drum shaped connection points at the bottom have stuck in the socket. I expect this is down to over-heating as it happened to one of my other halogen bulbs a month or so ago when I started to replace them. I had to get an electrician round to fix the socket then
Can anyone on here suggest any ideas on any of the above?

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Postby ericmark » Sat Jan 09, 2016 3:46 pm

It would seem you know the problem the dimmer switch is designed to run with a range of wattage and you have gone under the range it can deal with.

A LED need a constant current, but out house is supplied with a constant voltage. So some where we need a LED driver in the main built into the lamp which controls the current, to dim them the current is reduced so the dimmer switch needs to talk to the lamp and tell it how bright it should be.

A simple LED lamp with built in driver can often work at 150 ~ 250 volt AC so simply reducing the voltage will not make them dim at least in a controlled way.

It is the converting from voltage dependent to current dependent which separates good and bad LED lamps the base LED will give somewhere like 100 lumen per watt but by time it has gone through the driver which changes voltage to current it can drop to 50 lumen per watt.

There are three basic ways to control the current with an AC supply, A capacitor, a resistor or a pulse width modulated controller that latter is very good but expensive.

So the only way to be sure is to buy a dimmer switch and LED lamps which are the same make and designed to work together. However there are other ways that may work including putting a load on the dimmer switch so although your lamps are energy saving you are still using the same amount of electric which to me is cheating.

So step one is consider do you really want to dim your lights? With tungsten dimming the light also resulted in a red light which felt warm and homely but with LED the colour does not change. So with 12 lamps have 4 on one switch and 8 on the other and you have three levels of light without using a dimmer with just two switches.

The quartz bulb should not have been dimmed it reduced their life but many did, with the MR16 fitting be it GU5.3 (12 volt) or GU10 (230 volt) the MR referred to a multifaceted reflector and 16 was 16 x 1/8 inch and the multifaceted reflector would produce a spot of light ideal for lighting pictures and ornaments but rather poor for general lighting. In the main the LED does not have a multifaceted reflector but the LED its self produces a beam of light however this tends to have a more gradual edge to the beam.

One can get a LED equivalent to a MR16 rated 25-35º which are centre weighted most of the light in the 25º part but still some light in the 35º part so swapping can produce some unwanted effects and also some gains or losses depending how used in the area lit. I have seen where GU10 to E14 adaptors have been used and candle bulbs which point out of the holder but don't look too bad and give a much better spread of light.

Personally I find the LED a pain as they don't seem to replace like for like and when I tried to replace 10 x 8W CFL with 10 x 3W LED the room looked brighter where is should have looked dimmer as went from 3400 lumen to 2400 lumen. Also replaced a 5 foot fluorescent lamp 64W with LED at 24W however the lumen also dropped from 5600 to 2400 which was not really what I wanted room seems bright but try to read and one realises not as bright as it looks.
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