UV lighting using gel?

[daifuse]

I used congo in 4 cantata pc's in a u/v scene as well as the u/v canons in panto last year - I didn't bargain for some of the base costumes which were black showing up as red! (See Rob Sayers comments about the spectrum range of congo) Fortunately this became apparent during dress rehearsal necessitating a quick re-plot.

[J Pearce]

A slightly better gel to use instead of Congo is Ultimate Violet, but 4kW of pars in ultimate violet still only manage the same fluorescence that a 40W tube can, and the tube has a more even spread.

[indyld]

A slightly better gel to use instead of Congo is Ultimate Violet, but 4kW of pars in ultimate violet still only manage the same fluorescence that a 40W tube can, and the tube has a more even spread.

 

I'd be surprised if 4kW of PARs would even manage that for the reasons stated above. 707 also has the red problem and possibly more so, it's relatively double the amount of shorter wavelength peak in the indigo area allowed by the filter. This is why 707 is a lot more red than Congo, even with my dodgy colour vision and let's not forget that tungsten emits many times more at the red end than the visible violet end.

 

One would probably achieve better fluorescence by cutting a hole in the roof and gelling it up with Wood's glass! Of course, what we don't seem to have access to is any data regarding the relative transmission of UVA from theatrical gels which one assumes there is some so maybe L181 or 707 + L106 L115 (edit, brain fade) over all the windows MIGHT cut all those pesky visible wavelengths and leave some UVA emitting from daylight. :-)

 

The OP has yet to follow this up, the point about using a UV source has been well made by all here.

 

Edit. guh, I didn't mean 106 I meant anti-106 like a green blue.

[paulears]

The black going red phenomena often shows up in videos where congo is an active ingredient. Sometimes on the video it's so bad it's amazingly pink.

[Louis sullivan NLS]

Sorry I worded this a bit wrong, when I said the camera guy complains, it's not because he can't get a good UV effect on VT, the problem was having 4x 4ft tubes on the front of the stage with no way of covering them was creating 4x green glowing bars on screen.

 

Thanks for everyone's posts. The main issue I was having was the FOH bar is quite far from stage for smaller fixtures (atleast 8-10m) The FOH bar consists of in-house 12x 1000/1200w 18/34 profiles (Cantatas I think from memory, so not the best, will bring in some of my S4's for gobo stuff but that's another matter) so was a bit worried about the throw of a 400w cannon as last time had trouble focusing the in house rig due to distance from the stage.

[Ynot]

Sorry I worded this a bit wrong, when I said the camera guy complains, it's not because he can't get a good UV effect on VT, the problem was having 4x 4ft tubes on the front of the stage with no way of covering them was creating 4x green glowing bars on screen.

I think the comments still stand, regardless.

 

If the ONLY problem with using 4 ft tubes is with the video guy then that to me is a no-brainer.

That said, surely it would be a simple task to knock together a couple of bits of 4 x 1 timber (painted black on the audience side) to make yourself a screen for those fittings...?

[Tomo]

the problem was having 4x 4ft tubes on the front of the stage with no way of covering them was creating 4x green glowing bars on screen.

Ok, so find a way to cover them.

Perhaps you can rig them a bit higher, and maybe you can hang some drapes in front of them or use some blacktack or similar on each fitting to hide them from the camera position.

 

After all, that's the actual problem so surely that's the first thing to fix?

[paulears]

Get a new video guy. He's either in the wrong position, or lazy. Even if the bars are in shot and annoying - how long is the UV sequence. All the decent editors offer a range of tools to remove or mask these things. My attitude as somebody with feet in both camps is that you don't impact the live show for video - unless the video is the most important element - as in maybe it generates more income than the box office, or is a critical element for evidence collection. If it is an extra then it should blend in better. If it needs an hour or two extra in the edit, then that is what it takes.

 

If there really is anybody who hasn't seen a UV scene - click here but personally I hate them. Towards the end, the UV tubes are clearly in shot, and are untouched - they reveal as a dark blue bar and not a problem at all. If your camera reveals a brighter bar then the camera has a poor UV filter, or so cheap the chip doesn't have any UV protection at all - the cure, a cheap UV filter from ebay.

[Yorkie]

Our church panto will have a UV scene and I'm looking for advice on how to light it. The stage will be no bigger than about 8m wide and 4m deep. We have no bars above the stage so mounting options are limited to either:

* 4m stands either side of the auditorium

* lights on the front edge of the stage

* balcony rail mounting (12m from the stage and about 3m higher)

 

The church will not be blacked out (it has huge windows) but it will be in darkness apart from a couple of exit boxes. The simplest option would be for us to place a 400W cannon on the front of the balcony but I'm concerned that it might not be sufficiently powerful for the stage. I'm hoping to borrow a cannon and try it before we buy one, but I'd appreciate hearing now if anyone can already tell it will be completely inadequate. LED's have been recommended to me but I'm not aware of any products that will match a 400w cannon for £100

[paulears]

UV tubes, front of stage - you could easily have 4 or 5 for £100, probably less! Bright and if you put them in sealed fittings with covers, safe from glass smashing.

[Yorkie]

With this plus this I could get five of them wired up for about the same as a cannon and lamp. Lower wattage but much nearer the action

[adamharman]

FOH bar is quite far from stage for smaller fixtures (atleast 8-10m).... .....worried about the throw of a 400w cannon as last time had trouble focusing the in house rig due to distance from the stage.

 

Not sure about the throw, but the cannons tend to have a fairly wide beam so unless the stage is huge you're likely to cover half the audience as well from that distance.

 

I've got a couple if you wanted to try, but I'm probably too far away (Callington) to make it worthwhile.

[adam2]

With this plus this I could get five of them wired up for about the same as a cannon and lamp. Lower wattage but much nearer the action

 

I do not think that the fittings linked to will be very suitable.

The plastic covers not only absorb a fair bit of the UV but may also flourese and thereby add unwanted visible light.

If bare tubes are not safe, then I would use fittings that enclose the lamp in steel mesh rather than plastic.

These are available from most large wholesalers.

[paulears]

Well then I've been doing a pile of shows very badly then. The plastic covers on the ones we've been using ourselves and the very similar ones brought in by numerous shows work absolutely fine. They don't from a practical viewpoint absorb any UV - certainly the difference with cover on and cover off is simply some refraction from the corner edges, but that's only obvious as a comparison - in practice you don't notice anything. The plastic does light up a little, because it does reflect internally a little. Can I detect a loss of brightness? No. The ones we have do not seem to fluoresce themselves. We have covered the top edge and sides with black gaffer, and this is quite sufficient to prevent the audience seeing the UV. Tubes with slat glare reducers are no good, as they cut out quite a bit of light and produce odd reflections, but the mesh ones are fine - just much more expensive, and when given a hard kick, or dropped can still let glass escape.

 

For the price of these things, I really can't see any issues with them. We knocked up ours after seeing visiting crews with them - and would happily buy more in the future. You can't get a better feature for a risk assessment in a sensitive venue that having no chance of glass escaping instead of a low chance.