Dimming practicals with d0mest1c lamps

[pritch]

I suspect many theatres are in the same boat as us where the stock of incandescent lamps for practical lights on set is starting to dwindle.

There's actually a fair few incandescent lamps on eBay, so that's an option, but I do wonder how long that's going to work for in the long term - plus I expect it's only a matter of time before someone wants to use something with a built-in LED source on stage.

What solutions have people come up with? I don't really want to go throwing incandescent stage light dummy loads at the problem as we've got relatively limited options for doing that in a way that won't result in problems with light spillage onto stage.

I understand Betapacks need something like 0.1A to function properly - those tubular heaters that you sometimes see in outbuildings and the like go down to around 40W for the small ones and they're as dumb as a box of rocks in terms of control circuitry - has anyone tried something like that? It's hardly like putting a small heater on a wall high above stage is going to bother anyone.

[timsabre]

All LED lamps/sources are different, what works for one will not necessarily work for another (even the same brand sometimes).
Even supposedly "Dimmable" LED lamps will not dim well on a triac dimmer like Betapack, even with a dummy load. You can get random flickering or latching on of channels.
If you can get a trailing edge / mosfet type dimmer then they dim much better, but you will not get a smooth fade on from black. DMX-controllable trailing edge dimmers are hard to find, there are some chinese DIN rail modules on ebay which work.

ebay link: these say triac but they are actually mosfet and can be switched to trrailing edge mode. I have used these successfully to dim "dimmable" LED bulbs on stage.
https://www.ebay.co.uk/itm/276242880379

 

[pritch]

Interesting, Tim - and not a terrible price either!

[timsabre]

6 minutes ago, pritch said:

Interesting, Tim - and not a terrible price either!

Yeah - depending on your venue's view on electrical safety / certification etc it may or may not be acceptable as I doubt it complies to any particular standard. The one I've got is safely constructed inside but you never know what you are going to get from ebay.

The fully legitimate option would be the Artistic Licence Sundial units which are also designed to dim LED lamps but they are a lot more money.

[Tomo]

"Dimmable" LED lamps almost always means they'll dim around 20%-100% when on a reverse-phase dimmer, and flicker/snap out below that.
On the bright side, that's often (usually?) absolutely fine for a practical.

You'll generally need to configure the channel to have an appropriate "knee" or bottom-set to ensure they don't flicker - either in the dimmer or in the console - and will often want to set individual channel timing to ensure it snaps on/off at a sensible point in the fade.

I think it looks terrible when the practicals snap on first/off last, but it's usually fine if it snaps on/off at its stable minimum at an appropriate point during the whole scene fade.

[themadhippy]

 

Quote

I suspect many theatres are in the same boat as us where the stock of incandescent lamps for practical lights on set is starting to dwindle.

Make use of  the loophole,rough service lamps  are/were exempt from the regs and theirs still plenty of ole skool incandescent to choose from.

[adam2]

Trying to dim household LED lamps is in my view not worth the trouble.

Incandescent/GLS lamps are still fairly readily available on fleabay and elsewhere. And has been said, "rough service" lamps are exempt, as are "traffic signal lamps"

If you are concerned at future availability, simply stock up now. A couple of dozen lamps is not a lot of money nor a significant storage issue.

[sunray]

9 hours ago, timsabre said:

All LED lamps/sources are different, what works for one will not necessarily work for another (even the same brand sometimes).
Even supposedly "Dimmable" LED lamps will not dim well on a triac dimmer like Betapack, even with a dummy load. You can get random flickering or latching on of channels.
If you can get a trailing edge / mosfet type dimmer then they dim much better, but you will not get a smooth fade on from black. DMX-controllable trailing edge dimmers are hard to find, there are some chinese DIN rail modules on ebay which work.

ebay link: these say triac but they are actually mosfet and can be switched to trrailing edge mode. I have used these successfully to dim "dimmable" LED bulbs on stage.
https://www.ebay.co.uk/itm/276242880379

 

Ah I was looking at those the other day with a view to 2 situations:

1) To dim less than ~50W of LED  but the spec shows - 200 to 480W.

2)To operate a remote 500W linear flood where DMX and fixed power exist but I feel it's too close to the limit for comfort.

 

I assume you are comfortable with them, what power LED have you used them for?

I've used these several times with nothing but praise for them.https://www.ebay.co.uk/itm/355852374454?

 

Edited Monday at 07:19 PM by sunray

[timsabre]

I was dimming 2 lengths of cheapy Amazon festoon with G40 LED lamps - about 120 watts altogether. The lamps (decorative LED filament type) did not claim to be dimmable but actually dimmed perfectly. The dimmer I had would dim a single lamp at 2W so I am not sure what that "minimum" load is all about. It was possible to set a "preheat" level where the lamps were not lit but would give a smooth fade up from zero.

[J Pearce]

The filament LED lamps as far as I understand are driverless, meaning they dim quite well but can be prone to camera flicker (as they're flashing at 50Hz).

The fancy answer that the bigger shows are using is switch to low voltage LED lamps on proper LED drivers (either wireless or wired). There's a school of thought that says this removes a risk factor for on-set practical electrics too. 
Granted, it's a chunk more cash than a 60W bulb and a BC lampholder from Wickes...

[alistermorton]

I suspect that in the end, this is the way we'll all have to go.

[Yorkie]

I have a few dozen various incandescent domestic lamps to shift. Hoping to finish listing them in the next few weeks, for free collection or postage at cost. any specific requirements in the short term, please drop me a message