LED Lightsource

[Biskit]

So... in a mad moment earlier this year I decided it might be a neat idea to convert a Cantata Followspot (essentially a Cantata 11/26 with an extra handle and a colour mag, for anyone who hasn't come across the followspot variant) to LED. I mean, they're pretty sturdy and well balanced, nice and compact, well built, just... a bit dim by today's standards with a 1200W lamp. On a whim, I bought one of these:

 

https://www.ebay.co.uk/itm/High-CRI-97-High-Power-COB-LED-Daylight-White-5600K-47-56V-5-75A-300W-30000lm/312052272903?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

 

In my naivety, I thought sourcing a suitable power supply and heatsink arrangement would be straightforward, and I'd then just need to find a way to mount it in the existing lamphouse (stripping out the existing lamp holder, reflector etc). However in short, I haven't got a clue what type of power supply I need (ideally to allow manual dimming - external control eg. DMX would be handy but not essential) nor what type/size of heatsink. Can anyone help? I have seen similar projects on here a few years ago but much smaller in scale, much lower powered LEDs.

 

Or perhaps it was just a daft idea in the first place! Any thoughts?

[timsabre]

Have a look at Meanwell

Elgc-300h

 

You will need a substantial heatsink. The larger CPU heatsinks can be quite good but you need to take care to modify the fixture housing so that the hot air gets out of the housing.

 

Then there are the optical issues to resolve... That's probably the most difficult part as the fixture is designed for a lamp with a very small bright filament and the LED is a much larger source. You'll need some sort of collimating lens in front of the LED.

[Don Allen]

I was impressed with a 400W LED followspot when in Moscow a few years back, so think a 300W would not be bright enough. It may be an easier starting point to choose a LED Engine, but seeing as you have this as a starting point, allow for an upgrade to 4ooW in your calculations. For cooling, the larger the fan, the quieter it is and one supplier of quiet fans is quietpc in the UK.

 

You may have to mount your power supply underneath the lamp body. The one suggested is suitable for mounting direct and can be dimmed which is handy.

[musht]

1200W lamp was successor to the 2k back in the day.

 

Additional collimator is going to help, something like https://www.ebay.co.uk/itm/28mm-Optical-Glass-Lens-Collimator-Plano-Convex-for-Led-Projector/251557561702?hash=item3a91ffc566:g:STUAAOSwo8hTmgyQ

[Biskit]

Have a look at Meanwell

Elgc-300h

 

You will need a substantial heatsink. The larger CPU heatsinks can be quite good but you need to take care to modify the fixture housing so that the hot air gets out of the housing.

 

Then there are the optical issues to resolve... That's probably the most difficult part as the fixture is designed for a lamp with a very small bright filament and the LED is a much larger source. You'll need some sort of collimating lens in front of the LED.

 

Thanks for the pointers. Is this the power supply you're meaning? Searching for the term you mention brings up a confusing array of options:

 

https://www.mouser.co.uk/ProductDetail/MEAN-WELL/ELGC-300-H-AB?qs=w%2Fv1CP2dgqrHxp9oegnKRg%3D%3D

 

I did actually do a very small amount of crude experimentation before I ordered the LED. I got one of those LED torches, the small round black ones with a magnet on the back, an older type with a couple of dozen small LEDs in an array of similar size to the 300W LED I have bought. I found that by placing it inside the lamphouse, just behind the gate, it was possible to project an image of the LEDs by focussing the Cantata's lenses. It was obviously very dim, being powered by just three AAA batteries, but I felt proved the point that it should work. Moving the torch just a few mm back from the gate meant the 'image' of the LED array was diffused into an even circle, which could be usefully zoomed and focussed in the conventional way. An iris also worked as expected. On this basis I concluded that a much brighter LED of similar size will hopefully yield similar results, but with useful brightness.

 

In response to Don Allen's mention of it possibly being underpowered - I guess time will tell though as with anything I guess it depends on the application - I'm looking at relatively small-scale applications here so hopefully it'll be adequate.

 

Heat-sink wise, I guess I just need to look at the biggest I can fit in really? Noted the point about ensuring heat can escape. Fans and holes in the casing will be necessary I think.

 

Thanks again for the replies, and Happy Christmas to all!

[Jivemaster]

Heat! If the case suited a tungsten or discharge lamp then it's big enough BUT LEDs need lots of heat extracting at low temperatures so may need really good heat sinks. A glass envelope used to get to 200 -300C a chip base dies long before that.

[gyro_gearloose]

You'll have to stick with mechanical dimming if you want smooth dimming at lower percentages. According to the datasheet, and in line with most other Meanwell drivers I've looked at, the driver linked to earlier doesn't dim smoothly below 8%.

[graemeftv]

Its sadly all much more tricky than you might think

 

without writing an essay here.

we have successfully in the past got a strand cantata profile to run with a a msr 575w lamp with new reflector, external ballast. louver dowser on the front. all without spending a fortune on parts.

 

currently in the process of doing the same with some movers converting to led. manufacturing heatsinks, lenses etc

 

If anyone wants any help of advice, feel free to call the number on our website

[gyro_gearloose]

Are you converting spots or washes to LED? I have used small diameter 40W LEDEngin LEDs in place of discharge sources while retaining the condensing optics. The current crop of high current/brightness COB LEDs look like they are too big to simply be a drop in replacement in a spot, but I’m not sure that wouldn’t be a problem for a softer edge wash fixture.

 

I did exchange a few emails with a UK lens company trying to find a solution for using comparatively large diameter light sources in condensing optic systems. Nothing came of it in the end as they kept trying to push me toward using a skilled optic designer for what I thought would be a simple system to design. I think they thought I wanted the last word in optic precision, and not the fairly crude lenses usually found in theatrical fixtures.