Lighting an Art installation

[Tom]

This is for a piece of art being created to hang in a foyer - so a bit OT but I hope you will indulge me.

 

The piece consists of a 2m x 2.5m map mounted on a board, with a piece of clear plastic (perspex or similar) mounted in front of it, with a gap between. The plastic will have acetate or other coloured translucent plastic attached to it to indicate areas of the map.

It will look like this:

http://i1304.photobucket.com/albums/s535/tomalbu/Mapping_zps521e45ab.jpg

 

I need to light the Map image so it can be seen through the plastic / acetate. Front light is not an option, nor is building a light box. So I was wondering about mounting LED tape around the edge to light across the map.

 

Would this work?

Would I be best mounting it slightly forward, maybe actually on the perspex (something attached to the edge of the perspex), to give a better spread (I'm not sure what the gap between the perspex and the map will be, but I guess I could adjust that if required.)

 

I'm looking at the cheapest LED strips - 60 x 35/28 LED per meter (claimed around 400lm). Will a strip top and bottom work or do I need to go all the way round - I'm guessing the latter just to get an even spread but the place it is going to hang is not very brightly lit, with very little (if any) outside light to fight against so it doesn't need to be very light.

 

 

Any thoughts?

 

T

[timsabre]

Um, sorry if I am stating the obvious but if you light from around the edge, the middle will be dark.

The LED tape will be very glaring as well which will make the map look even darker.

 

I think backlighting is your only option, but don't think light box - I have used some light panels from Rosco which are an edge-lit flat sheet with some sort of engraving which spreads the light out evenly across the panel.

 

for an example see http://www.rosco.com/litepad/litepadDL.cfm?menuReturn=litepadMy link

 

 

The ones on that page are quite small but they do bigger ones. I am sure there must be other suppliers of something similar, it's only physics after all.

[ImagineerTom]

Edge lighting (with ANY lighting technology) something 2.5 x 2m isn't going to work, If front lighting is out of the question then some sort of lightbox is your only solution - possibly LED based with the space divided in to 20cm "squares" to keep the colour even - it could be relatively slim though.

 

I'm spotting much much bigger problems with the concept though - have they looked up what a piece of clear plastic that size (in a suitable non-scratching, building regs compliant) material will cost and for that matter just how thick it would have to be to have even enough strength to hold its own weight let-alone anyone brushing against it? You're looking at a 5 figure sum just for the construction of the basic physical elements of this piece so you definitely shouldn't be considering lighting it using the cheapest LED tape technologies.

[Dave m]

does the back have to be foam board?

 

If it was some kind of printed transparent material, it could be backlit with something like a profile.

 

 

there is some kind of kit that estate agents are using in their windows that relies 9I assume) on the bare wires that support the pix of houses that seems to supply a backlight system

size may be an issue

[Brian]

Electroluminescent panels with the map printed on a clear overlay?

[timsabre]

Electroluminescent panels with the map printed on a clear overlay?

 

An EL panel of that size should quickly deter any finger pokers... bzzt...

[Tomo]

I'm spotting much much bigger problems with the concept though - have they looked up what a piece of clear plastic that size (in a suitable non-scratching, building regs compliant) material will cost and for that matter just how thick it would have to be to have even enough strength to hold its own weight let-alone anyone brushing against it? You're looking at a 5 figure sum just for the construction of the basic physical elements of this piece so you definitely shouldn't be considering lighting it using the cheapest LED tape technologies.

I have no idea how you'd get to that kind of figure, I'd estimate around £2-3k. Not cheap, but nowhere near five figures!

 

A clear 12mm polycarbonate sheet that size is around £850 ex delivery.

LED strip's about $1-2 per metre on your doorstep, plus LED drivers, printing, machining and manpower.

 

Polycarb's easy to work so machining costs are very low, and while it scratches more easily than glass it is extremely tough and that kind of thickness will survive a thrown brick!

It's usually Class 1/Class 1Y (self-extinguishing) so can easily meet the fire regs.

It's what they make bus stop shelters and riot shields from.

 

(Clear acrylic that size is cheaper but is flammability class 3 or 4 which is nasty. Acrylic's relatively fragile as well.)

 

Foam board cannot be structural this size. It has no stiffness, you'll need to support it at close intervals

 

As already said, if it cannot be frontlit then it needs to be backlit. There's a reason big TVs are "LED" backlit!

 

An array of cheap LED strip will work fine as backlight - you will need a lot though, and be sure to buy plenty of spare because some will fail.

Just remember that the shallower the lightbox the closer the LEDs must be.

- Test with a small section of the diffuser material to find the depth you need to avoid blotches.

[ImagineerTom]

A piece of Polycarb 2.5 x 2m is going to have a fair bit of wobble in it - supported only around the edges (as diagram suggests) won't have any real effect unless there's some sort of substantial frame hidden behind the map that's actually providing some real structural re-enforcement and even then the sheet wouldn't be especially stable - it would either need some sort of extra support in the middle or be thicker (my instinct is saying 18mm)

 

So a large sheet of polycarb, the hidden subframe, the map itself, the extra artwork, the rear lightbox structure, a LOT of led tape, a heavy-duty power supply for all that light, a good few days assembling it and some manpower (and vehicles) as this is going to be weighing 150kg quite easily and you're hurtling towards £10k without too much effort

 

 

 

[Tom]

Thank you for all your concerns about the structure and it's enormous cost.

 

I'm really only asking for advice about the lighting element though as I'm perfectly qualified to deal with the other issues. I don't feel the need to burden you with all the parameters involved which you would need to know in order to realistically advise, comment or quote on the other elements of the project.

 

I don't think it's a realistic possibility but could somebody talk me through the

An array of cheap LED strip will work fine as backlight

concept please.

 

Change the foam board for something translucent - white polycarbonate (with all it's structural issues)?

What sort of spacing are we talking between the LED strips and between the then and the backing material?

 

The LED's I'm looking at quote a 120 degree spread.

 

 

Going momentarily back to the side light idea (and expecting to be shot down)

Um, sorry if I am stating the obvious but if you light from around the edge, the middle will be dark.

The LED tape will be very glaring as well which will make the map look even darker.

 

How about I build a lip around the edge for the LED to sit behind to reduce the direct glare issue - as when they are used architecturally?

 

Obviously it will be darker in the centre, but I wonder how awful this will be, compared to a not lit at all option. I'm now only talking about a 1m "throw". This seems to be the sort of application I see them used in often, or am I misunderstanding. This project does not have to be perfect.

 

What I should really do is get hold of a strip and have a play / show the artists involved. Anybody in North LOndon got a spare bit of tape and a power supply I could borrow for a day? Or even just the power supply and I can invest in a meter of tape.

 

Thanks for your help.

 

T

[ImagineerTom]

The LED's I'm looking at quote a 120 degree spread

 

Well from this information alone (and assuming you have GCSE maths or equivalent) you can work out PRECISELY how raised up from the surface of the map your LED strip would need to be to stand any hope of casting light across the whole surface, or PRECISELY how deep your light box would need to be with different quantities/spacing of the LED tape and give a consistent and relatively even light spread.

 

Maplin sell LED tape by the inch and you can power it from a battery - however it's pointless doing any research with anything other than the ACTUAL tape you're planning to use as there is a massive variety of brightness's, angles and LED spacings so just because it works with a sample piece doesn't mean it will work with anything else.

 

 

(oh and ignoring light decay and reflection/refraction caused by the adjacent surfaces, your "side light" would need to be around 58cm proud of the map surface to give an even spread - though that could be reduced by around half if you could somehow angle the strip so that it was more like front lighting - and for the rear lightbox idea assuming the LED units are 1" apart on the tape then your rear lightbox could be as little as 9mm deep if you arranged the tape so that you ended up with a "grid" of LED's with 1" spacing between them.)

[timsabre]

If you light from the side, the brightness falls off very rapidly as the angle between the surface and the light source becomes flatter and flatter. You will get a strip of about 2" lit, the rest will be dark.

 

Never mind testing with LED strip, just use the LED on your phone, you will see straight away.

 

 

For backlighting you will need a light box depth about equal to the LED spacing, to avoid blobs of light. Basically you cover the whole back of the thing with LED tape.

[Brian]

Tom, I don't know if your budget goes as far as buying something to take apart to see how it's done but I just spotted this in a Rapid mailshot...

 

[musht]

There are several different ways of getting edge lit plastics to forward emit, if your reading this on a flat screen your looking at one.

 

For slim light boxes , sign industry is place to start looking, first page off of google

 

http://www.w-co.co.uk/light_boxes.php

 

Guessing by drawing though that coloured parts on spaced layer above map are part of artists concept and circles straight onto map may not be acceptable?

 

Means the heavy sheet of polycarb or acrylic in front,as well, polycarb is more impact resistant but scratches easy, can also have a bit of a blue tint in thick sheets.

 

5050, three die per LED , tape is a lot brighter than 3528, one dice per LED, tape.

 

High power LEDs with letterbox, elliptical optics might give a more even coverage but show up any wrinkle or bump in the map.

[alistermorton]

I thought this flat screen monitor had an electroluminescent panel behind it - I'm not at all sure that is edge lighting.

[timsabre]

Most modern monitors (last 5 years) have edge-lit LED backlight, but getting an even light from edge lighting is very hard. They used to do it with a parabolic-shaped back panel which curved up towards the screen surface, gradually reflecting more and more of the light as it got further away from the LED. But now they tend to use clever engraving to gradually diffuse the light.