G4 LED Light Flashing Mystery After Replacing Original 20W Bulbs


Postby Benchillian » Wed Feb 17, 2016 6:39 pm

I have a ceiling light with 5 x G4 bulbs. Last week, I replaced the 20w original bulbs with 2.2w 12v LEDs.

At first, there was a bit of a flicker with the new LED bulbs. So I pushed them to make sure they were properly 'in' and all seemed fine.

When I switched them on today, there was more of a flicker, then after a few minutes they all began to flash on and off in in synch.

I took the LED bulbs out and put the old bulbs back. Result: working perfectly.

Can anyone tell me what's going on, please?
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Postby ericmark » Fri Feb 19, 2016 11:20 am

I will have a good guess. The power supply is a switch mode or pulse width modulated really two names for same thing, and it works by altering the mark/space ratio, the problem is they have a minimum and well as maximum output and likely min = 20W i.e. one bulb and max 100W i.e. all bulbs. 5 x 2.2 = 11W which is below the minimum output. It may work with 4W LED lamps but there is more than simply output. The LED as the words suggest are diodes so require DC, there is clearly some rectifier to make the AC into DC inside the bulb but the wave form out of the voltage regulator is unlikely a sine wave and also unlikely 50 Hz so adding the electronic components within the bulb can do all sorts, it could build a transmitter and could cause all sorts of spikes causing TV and radio interference. Also with such a unknown supply life of the bulbs is unknown.

I tried so G5.2 MR16 12 volt LED's in my case with a real transformer but the LED's lasted just 6 months, yet all my low voltage LED's (230vac) are running without a single failure.

For small low voltage (230vac) bulb type lamps the LED works well, for extra low voltage (12 volt) it is rather hit and miss, also for the larger lamps LED has very little advantage of fluorescent lamps an LED gives around 60 to 100 lumen per watt, and fluorescent is 80 to 95 lumen per watt as a tube or single fold in the tube, but with multi-folds it goes down to 40 lumen per watt, however some colour changing LED go down to 20 lumen per watt.

In the main the LED its self is very good, but something has to convert constant voltage into constant current and with very cheap units that device is a simple resistor so as a unit rather poor lumen per watt.

I have also found the colour temperature of LED lamps is rather high 2700K to 3000K which makes one think they are brighter than they really are. Great walking around the room but try reading a book and you realise not enough light.
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Postby Benchillian » Sun Feb 21, 2016 10:12 am

Many thanks for the reply.

I might try leaving one or two of the original 20w bulbs in and see how that works. Or find a new ceiling light.
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Postby ericmark » Sun Feb 21, 2016 1:48 pm

Using one original bulb should work, it should be designed so that it will work with one bulb, however many are not, let us know how you get on it may help others with same problem.
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Postby Benchillian » Tue Mar 15, 2016 7:31 pm

Sorry for delay coming back on this. Got diverted by a job in the loft.

Tried the light today with 1 x 20w halogen and 4 x LEDs. Working fine. The halogen looks slightly warmer than the LEDs, but it's not very noticeable.

Thanks again.
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Postby ericmark » Tue Mar 15, 2016 11:36 pm

When the halogen blows will you remember why the rest of the lights are flashing?
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Postby Benchillian » Wed Mar 16, 2016 9:40 am

True!

At least I've got another 4 spares if that happens. Or I might just get a new ceiling light.
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Postby ericmark » Wed Mar 16, 2016 9:49 pm

Beginning of this year I removed last of the dimming switches, and down to one room only, the bath room with extra low voltage lamps. I bought some really cheap lamps £1 each from Pound World just so it looked OK and the original pendent lamps gives out enough light, however within 6 months they had failed, the only LED lights to have ever failed. I have a proper transformer so in theroy using 4 x 0.58W is not a problem. I fancy buying some better lamps but not into the 6 months life. Maybe more expensive ones will last longer but they were only fitted as a fad thought they looked good at the time.

So now have to decide new bulbs, or plaster up the holes.
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