LED Lights

[psynegy]

If I were to purchase this item: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...4951625fff6c383

 

Would it be dimmable (after plugging into a 15A dimmer socket)?

 

It says that it's 240v with no transformer, just wondering if there were any other requirements?

 

Cheers!

[Guest lightnix]

Would it be dimmable (after plugging into a 15A dimmer socket)?

No.

[tom_the_LD]

You NEVER plug LED lighting into a dimmer - LED lighting requires hard power; this is just power from your normal wall socket which is constant. You then run a DMX line from your controller into the lantern. You then mix the RGB levels to give you the mix you want and dim them that way.

 

HTH!

[david.elsbury]

Tom, did you even bother to click on the Ebay link in the OP? Had you done this, you would have seen the item in question is a LED fairylight-style net.

 

Perhaps you could do some research before making posts that make you look silly?

[niclights]

You then run a DMX line from your controller into the lantern. You then mix the RGB levels to give you the mix you want and dim them that way.

 

Not with these you don't. They are plug in and go. On or off. Just simple xmas lights.

[Biskit]

Would it be dimmable (after plugging into a 15A dimmer socket)?

No.

 

Hmm from looking at the e-bay page I don't see any major reason why not... it may require an additional load (500w lantern or something) on the same dimmer to get the load up a bit.. The specs don't state a power rating (that I can see) but LEDs are usually very low power draw. It also depends what type of dimmer you have.

 

If it were me, using my own gear, I'd probably give it a go. That isn't to say I'm advising you to do so (especially with someone else's dimer!), or that they would dim smoothly. I reckon it would probably work though.

 

HTH

 

Ben.

[tom_the_LD]

Tom, did you even bother to click on the Ebay link in the OP? Had you done this, you would have seen the item in question is a LED fairylight-style net.

 

Perhaps you could do some research before making posts that make you look silly?

Strange - for some reason the Ebay link didn't show up when I clicked on the thread earlier. ;)

[pritch]

We have something quite similar, which does get plugged into a dimmer from time to time. I've never needed a dummy load, but then again, our stone-age dimmers are notorious for being able to dim pretty much anything you care to plug into them.

[psynegy]

I believe our dimmers are Zero 88 Beta Packs...

 

So that sounds promising then, awesome. Cheers for your help guys! ;)

[PhilB]

Wasn't a problem for me when I used a set of LED Christmas lights for a show!

 

I did use a 500w fresnel as a 'dummy' load just to be on the safe side!

 

Good luck!

 

Phil

[david.elsbury]

Right, here's time to clear up some apparant misunderstandings and misinformation.

 

Tungsten lamps have a linear dimming curve. Smooth. So, if you reduce the voltage to , say, a 500w fresnel, it dims smoothly and at an even rate from full to 0.

 

LEDs do not dim in the same way. If you reduce the voltage to an LED you will eventually hit a point where the LED turns off. This is because LEDs have a particular forward voltage, which the supply voltage must be at or above in order for the LED to illuminate.

 

There are ways to dim LEDs, the most common being PWM (pulse width modulation) of the current to the LED. THis is considerably more complicated than just lowering the voltage however.

 

The set that the OP linked to has a transformer to convert from the high voltage supply (240v) to a low voltage supply (probably 12 or 24 volt) for the LED strings. The LEDs will most likely be connected in strings in series, then the strings in paralell to the supply (as pictured below).

 

http://i44.tinypic.com/9tkhgn.jpg

 

Note: It is possible to put a transformer on some dimmers. You may or may not need a dummy load depending on the dimmer. I can see where some people would say that it is therefore possible to "dim" LEDs because they are on a dimmer.

 

But if you want to have the string dim smoothly from 100% to 0%, this is not the way to do it.

 

Are we clearer now?

 

More LED info at http://en.wikipedia.org/wiki/LED

[musht]

Right, here's time to clear up some apparant misunderstandings and misinformation.

 

Tungsten lamps have a linear dimming curve. Smooth. So, if you reduce the voltage to , say, a 500w fresnel, it dims smoothly and at an even rate from full to 0.

.....

 

.........The set that the OP linked to has a transformer to convert from the high voltage supply (240v) to a low voltage supply (probably 12 or 24 volt) for the LED strings...............

 

Tungsten dosen`t actually dim linearally the curve at the dimmer is normally corrected to reverse the S curve effect of linear dimming tungsten or not in case of Multidim :-)

 

To quote the op`s actual link

 

"They run direct from the UK style mains power plug, so they do not require a transformer."

 

They are probably series wired with dropper resistors directly to 240V mains, they will probaly happily plug into a dimmer but may require a ghost load.

 

George Squre in Glasgow`s Christmas lights are getting replaced gradually with LED ropelight, 240V ,no transformer plugged into ACT6s, Big Clive is the man to explain more if he is about.

 

For dimmable define diimmable, the actual effect as they`re diodes is to rectify the mains, some types have an inline rectifier box in the mains lead, some don`t, which still isnt a transformer, so they dim on a 50Hz PWM scheme, they will lower in intensity but it will be very steppy and 0-100% smoothly isnt going to happen.

[Biskit]

Are we clearer now?

 

While I generally agree with the science of what you've put...

 

1. I disagree that tungsten lamps dim linearly (ie. lumens out proportional to RMS supply voltage) however I accept they dim 'smoothly' ie. no sudden step off.

 

2. The product indicated does suggest no transformer involved so I suspect simply series LEDs perhaps with limiting resistor.

 

In short - theory correct, however in practice it is certainly not uncommon to see LEDs dimmed crudely using a conventional dimmer, whether via a transformer or simply lots in series. Several companies I've worked with have LED starcloths (basic 'all on' plug in and go type) which were regularly run through a dimmer. There was the slightly annoying step off at the bottom but apart from that, dimming was pretty smooth. Certainly perfectly useable 99% of the time.

 

Ben.

[bigclive]

I believe the mains Funky Lighting type are indeed the strings of LEDs run directly across the mains with a rectifier and a multiple of series resistors in-line. As such they should dim fine, but will sometimes require an extra load on the dimmer to make the dimming more stable.

 

As Adam mentioned, I've been gradually replacing the Xmas lights on George Square in Glasgow with new LED FX or refitting the older effects with LED tubelight. The internal construction of the tubelight is generally in two styles. A string of LEDs followed by a string of resistors that are then laid back over the gaps between the LEDs, or a string of alternate LEDs and resistors. Either way, the good quality stuff has loads of heatshrink and a modest length of flexible wire between each component and this is all crammed into the channel within the inner core of the tubelight before the outer sheath is applied. That must be quite a task, since the actual length of the circuitry in each metre is almost 2 metres in length. The extra wire helps make the product supremely flexible and also helps somewhat in keeping the heat of the resistors away from the LEDs. The socket that plugs onto the end of the tubelight connection spikes generally has a full wave rectifier built in.

 

There are typically between 20 to 35 LEDs in a series string for mains operation, so the string will generally begin conducting at about 70V for red or yellow LEDs to about 100V for green, white and blue. This does affect the dimming curve to a degree, but when I dimmed the LEDs on George Square it really didn't show.

 

The biggest problem I had was ghosting of the LEDs when the dimmers were at zero, because the snubber network passed enough current to make large areas of the lights illuminate at a very visible intensity at night time. The first time it happened was the night before the big switch-on, so we had to make a whole load of low power resistive shunt loads by hacking up some spare mains tungsten light strings and putting 15A plugs on them. The sheer number of channels and available space ruled out the use of higher power lights as shunt loads.

 

Personally I think that Funky Lighting's best product is the UV LED string. They are a string of deep blue LEDs that are verging on UV, but are close enough to the blue side of UV to be very intense. They are a deep psychedelic purple colour that is hard to focus on. It makes them look like they are floating in the air.