Backlighting a stained glass window (on a budget)

[Stuart91]

One of my customer's venues has a set of three large stained glass windows. Each roughly 15ft tall, by maybe 4ft wide.

 

They're looking to backlight them so that they look good to people passing by outside. Ideally they'd like to be able to control the intensity remotely, and already have DMX running around the building.

 

I've seen this done in a few places by simply pointing LED security floods at them. Cheap, effective, but relatively unrefined.

The other approach I've seen (for a film shoot) was pointing a pair of profiles at each window, and shuttering the beams down so that they were lit very precisely.

 

I'm pretty sure that these folks don't have the budget for half a dozen LED profiles, plus mounting points are going to be hard to come by.

 

Can anyone suggest fixtures that might be good for this? I don't think there's a dimmable security flood out there, the closest equivalent I can think of is molefay-style LED blinders, which gives the controllability but seems like overkill.

[sandall]

Do they mind how it looks from the inside? If so, then you're stuck with fresnels or profiles. Underrun halogen might not be as "green" as LED, but will still give a long lamp life.

[Stuart91]

Do they mind how it looks from the inside?

 

I've highlighted to them that bathing one end of the room in security floods will feel a bit strange for those sitting in relative gloom elsewhere.

 

I suppose it might be nice if I could find a beam angle that minimises spill, but I suspect that might not be possible.

 

Uplighting was another thing they suggested, but I'm not expecting that to work very well. Light aimed through the glass is what I think is required.

[bruce]

Or maybe a diffuser inside?

[adam2]

The best results may be obtained by hanging on the inside of the window a white diffusing screen, products are sold for this purpose, but white bed sheets work well. Light the inside of the white screen as evenly as possible with whatever light source you have.

 

Directing lights directly at the windows from the inside works to an extent but not that well. Most stained glass is transparent, not translucent. As a result, internal lights directed upwards towards the windows waste much of the light skywards.

Light at head height or above will be very glaring to persons outside and in the path of the beam, and not very effective at other viewing angles.

[Don Allen]

Try some LED tape inside a L shaped white conduit, about 25mm size, on the edge of the window sill away from the window to allow maximum dispersion. The L shape keeps the light on the windows and stops spill back into the church. There will be reflection off the glass, but it won't be spoilt by direct light from the LED strip. Use budget LED tape to try it out and just some masking tape to simulate the cuttoff of the LED. You made need two or three thicknesses of the masking tape to get an opaque "barn door".

[Stuart91]

Thanks, that's all very helpful.

 

The windows are quite high up from street level - they're at the top of a raked balcony which is itself up two flights of stairs from the street. That's probably got some bearing on the angle we light it from. Viewers will be arranged quite widely horizontally, in fact most of the foot traffic will be along a major road that runs along one side of the building, the windows are on the end wall at 90 degrees to that traffic.

 

Unfortunately I won't be able to put any diffusers etc. behind, as the windows need to be seen by those inside as well (but they have the benefit of sunlight, during daylight hours at least)

 

Ringing the windows with some sort of LED tape wouldn't be out of the question. Potentially quite a fiddly scaffolding job to get it installed, but it might be possible to do that whilst they're redecorating and have the scaff in anyway.

[Robin D]

Similar problem in a ancient department store a few years ago, but on a smaller scale, we put clear plastic diffuser similar to https://www.cutmyplastic.co.uk/light-diffuser/ hung just on the inside. It did a great job when lit viewed from outside, and was virtually invisible when views from inside during the day as it was only an inch or so off the glass. An unexpected benefit was that we could then project on to it for indoor events at night.

[ImagineerTom]

Surely some d0mestic spot bulbs in aesthetically pleasing off the shelf light fittings would be a better, cheaper solution than going down the relatively industrial path of using theatre lanterns?

[Robin D]

Surely some d0mestic spot bulbs in aesthetically pleasing off the shelf light fittings would be a better, cheaper solution than going down the relatively industrial path of using theatre lanterns?

That's true. From memory we used two r30 reflectors in existing lighting tracks.

[sandall]

When you walk past an occupied church at night in most cases the windows you see are lit by multiple small light sources, i.e. a very big, but probably not very bright, soft-light, but if that church is floodlit from the outside you would need quite powerful lights focussed on the windows to give the same apparent brightness of image. As with any "effect" lighting, contrast is all. How much the street-lighting spills onto the windows is going to affect how bright your window lighting needs to be.

 

E2A: The contrast-ratio of your glass will also have a big effect - pastel shades won't need a lot of illumination; heavy dark colours probably will.

Edited March 18, 2021 by sandall

[kerry davies]

Sandall is right on several counts especially ambient light being a killer.

 

When we filled churches with trees and bushes or even just removed all the pews the effects of strong direct sunlight were amazing. The beams and rays gave the space a wonderful ambience. You couldn't actually see the stained glass windows but it looked great inside.

 

To see the windows themselves best needed bright but indirect sunlight. For that reason, if no other, I would avoid theatre lights like the plague. If you wanted great effects in mist and fog then yes, use beams but otherwise I would look to floodlight the immediate interior at the window and avoid direct light entirely.

[Junior8]

The one time I was asked to do this I used floods on short stands about 2 ft below the sill and six foot back. I didn't have any choice really about the position but it looked quite good provided you kept the intensity low. The plain fact is though that this is a very difficult task if the lighting has to be invisible inside. My first step would be to get a few sources and try things out - it may be that on looking from the street you find within two minutes that the whole idea is a waste of time. If the aim is to give a realistic impression you might be surprised just how little light is perceived through stained glass where there is any amount of ambient light outside.

[sandall]

The whole point about stained-glass windows is that they are meant to be seen from inside, not outside (where in daylight they can often look black), & rely totally on outside being brighter than inside (why when filming in a church you need a lot of very big lights outside the windows). To get maximum punch you need a decent flat-field beam just out of the eyeline of punters on the street, but as this is probably not practicable (& would give horrible reflections in the room) any of the previous suggestions, or even a dangling 60W-equiv remotely-controllable LED, might give a worthwhile effect. What do the windows look like when the normal room lights are on?

[TomHoward]

We had to do some large scale ones from the opposite side for a temporary event - it was a lecture on the history of the stained glass windows, which helpfully was being held on a winter's evening - we used floods in the end (400W halide) but after a bit of experimentation found silver/chrome barn doors really helped the beam shaping to get maximum light and reflect all the spill forwards from the 180degree (or more) untamed beams of the floods.