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LED Dimming

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Vic20/08/2019 13:27:48
2206 forum posts
11 photos

I’ve ordered one of these for a particular job.

**LINK**

And I may require a dimmer for it. I’ve heard of lots of problems with light dimmers such as buzzing noises and flickering. I don’t need or particularly want a “normal” light switch but instead will probably use an enclosure and a couple of IEC sockets.

Someone has recommended I use a variable voltage unit like this.

**LINK**

The only thing that concerns me is that it says 220 volt input so would this be ok for UK mains?

not done it yet20/08/2019 13:46:46
3240 forum posts
11 photos

When it gets to the working end, LEDs are operated with DC - or only on half-wave AC. They each actually require only a small forward voltage of about 0.6 volts before they start to conduct and they can/would thermally run away if the current is not controlled/limited. So I’m unsure as to what this proposed power supply will do for you.

220 volts is well within the voltage range supplied by the grid. Our supply could be as much as 254V, but everything supplied for 220V should be OK as most(?) items bought in the UK will bear this voltage on the rating plate.

KWIL20/08/2019 14:02:57
3111 forum posts
56 photos

LED dimmers do not vary the voltage, they vary the period of time (ie part of mains waveform only) during which power is applied to the LED.

I neither have buzzing nor flicker with typical light switch dimmers.

John Haine20/08/2019 14:05:16
2591 forum posts
133 photos

That power supply is totally unsuitable. The lights you linked to are low power 220v (fine for UK) dimmable LED bulbs. I suggest that you use a standard LED dimmer such as this which is made for the job and available from B&Q.

Vic20/08/2019 14:25:58
2206 forum posts
11 photos

I was originally looking at this.

**LINK**

As a standard switch plate it’s a bit bulky but perhaps I could remove the working parts from the plate.

As far as the dimmer I linked to in the OP it does say it’s a dimmer and also that it’s suitable for lamps?

John Haine20/08/2019 15:02:50
2591 forum posts
133 photos

Yes, but you hardly need a 4 kW dimmer for a 20W lamp! And LEDs don't dim very well with simple Triac dimmers. That unit would probably work fine with a big beefy incandescent spotlight.

How about this:

**LINK**

?

Frances IoM20/08/2019 16:27:40
637 forum posts
24 photos
rather than ordering from epay where there is little control over quality I'd suggest find your nearest trade dealer eg City Electrical, TLC (they have a useful paper catalogue), Rexel etc and buy matching lamps + dimmers - they will usually give trade discount if asked + have advantage stuff can be returned if faulty To back up John's point - most dimmers intended for heavy loads have a minimum load that far exceeds a puny LED lamp.

Edited By Frances IoM on 20/08/2019 16:29:31

Edited By Frances IoM on 20/08/2019 16:30:04

JohnF20/08/2019 19:22:57
avatar
852 forum posts
102 photos

Hi Vic, I have LED downlight's with a dimmer switch and they work fine, originally they were 12v Halogen lamps and i was intending to upgrade to LED lamps but very recently had some problems with 3 units that were around 9 years old so decided to dump the lot and fit new 240v LED units from CEF and the also work perfectly.

John

Andrew Johnston20/08/2019 20:46:10
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4778 forum posts
538 photos
Posted by not done it yet on 20/08/2019 13:46:46:

They each actually require only a small forward voltage of about 0.6 volts before they start to conduct...............

That might be roughly true of a silicon diode but it ain't so for an LED, as they don't use silicon as the semiconductor. As a rough guide forward voltage drops of LEDs are as follows:

Red ~2V

Yellow ~2V

Green ~2.1V

Blue ~3.3V

White ~3.6V

Like silicon diodes the forward voltage drop of a given LED is dependent upon the exact type, manufacturer, forward current and probably the phase of the moon.

Andrew

Nick Clarke 320/08/2019 21:09:33
avatar
359 forum posts
9 photos
Posted by Andrew Johnston on 20/08/2019 20:46:10:
Posted by not done it yet on 20/08/2019 13:46:46:

They each actually require only a small forward voltage of about 0.6 volts before they start to conduct...............

That might be roughly true of a silicon diode but it ain't so for an LED, as they don't use silicon as the semiconductor. As a rough guide forward voltage drops of LEDs are as follows:

Red ~2V

Yellow ~2V

Green ~2.1V

Blue ~3.3V

White ~3.6V

Like silicon diodes the forward voltage drop of a given LED is dependent upon the exact type, manufacturer, forward current and probably the phase of the moon.

Andrew

While I totally agree with you - the issue is that a commercial LED bulb consists of an LED light source and the electronics to drive it off the mains - and you cannot 'get at' the LED itself. You need to use a dimmer designed to dim the electronics not the LED as has already been suggested.

Edited By Nick Clarke 3 on 20/08/2019 21:10:13

Joseph Noci 121/08/2019 07:35:33
536 forum posts
832 photos
Posted by Nick Clarke 3 on 20/08/2019 21:09:33:

While I totally agree with you - the issue is that a commercial LED bulb consists of an LED light source and the electronics to drive it off the mains - and you cannot 'get at' the LED itself. You need to use a dimmer designed to dim the electronics not the LED as has already been suggested.

Edited By Nick Clarke 3 on 20/08/2019 21:10:13

Nick is quite correct - And therein lies the problem. most of those driver electronics are basic buck switchmode types, with constant current control to the LED in the lamp. So, varying the input voltage ( the mains) has , over a very broad range, no effect on the LED's brightness, as the controller simply adapts to ensure the LED receives a constant current. So, many of the basic LED lamps do NOT dim , or do not dim well. You may notice the splurb on some lamp's packaging indicating that the lamp is dimmable - That is there for a reason...

Some LED drivers ( the electronics inside the lamp) may dim, sort of, as the input voltage is varied down to a level. The electronics will increase the pulse width in its control loop, trying to keep the LED happy with enough current, until the PWM controller runs out of input voltage and the control loop is simply fully on - the PWM pulse width is then at max, and as you drop the input voltage further, the voltage of the pulse drops as well, and so the lamp dims.

The effect is that at full volume, the lamp is brightest, with NO change in brightness as you dim down, and then suddenly , at some point, it starts dimming. Dimming further most often results in the lamp dimming and then just cutting of, before you reach minimum setting on the dimmer, where the PWM controller itself runs out of functional voltage. During this dimming process, some lamps not intended for dimming even succeed in popping..

Just try make sure the lamps you use indicate they will work with conventional wall dimmers...

Joe

 

And also, as has been mentioned, Hi powered dimmers don't really work well on with low power lamps, esp the more common Triac dimmers - they start flickering at the low settings and drive you mad. There are more specialized wall mount dimmers that work with low wattage lamps. I have fitted dimmers that specify down to a 10watt load, using them on a 25 watt reading lamp above the bed headboard..

Edited By Joseph Noci 1 on 21/08/2019 07:40:00

Michael Gilligan21/08/2019 08:02:26
avatar
13801 forum posts
599 photos

Predictably thorough post, Joe yes

I would just add that Vic's lamp is branded Ranpo, and stated to be dimmable.

Their low voltage stuff is excellent, 'though I have not used the mains-powered lamps.

Ranpo's own website might be worth browsing: **LINK**

http://www.ranpolighting.com/

MichaelG.

.

P.S. http://www.ranpolighting.com/adjustable-controller-led-dimmer-switch-for-dimmable-light-bulb-lamp-110v-220v-p00285p1.html

Edited By Michael Gilligan on 21/08/2019 08:10:31

Vic21/08/2019 13:31:02
2206 forum posts
11 photos

I’ve ordered one of these, hopefully it will work ok.

**LINK**

old mart22/08/2019 22:16:06
442 forum posts
42 photos

Vic, that looks like a domestic dimmer module, try it out as bought to see if the lamp dims ok before attempting to adjust the low setting. I found that lowering the output from the factory setting just caused the leds to flicker, so I had to return it to the original setting.

I have found that the same dimmers that work with halogen lights, also work with the dimmable led lamps.

Edited By old mart on 22/08/2019 22:19:10

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