I’m starting to work on another LED piece. As I’m researching materials, I’m trying to figure out what’s best for diffusion. I’ve seen a number of projects here that have diffusion. For my project I’ll likely need something around 30" x 30". It would be great to hear what some of you are using (I’m especially looking at you, @Daniel_Garcia ).
On a related note, when you have a larger project like this, how do you mount the diffusion material without seeing the support structure below?
Have you looked at theatrical gels? Rosco or Lee? cut to size & stretch over a frame…hold down with staples or tape…second frame to hide the staples……
That is an interesting idea. In my younger days, I was involved with technical theater, but I didn’t think about this. I was thinking more along the lines of some thicker / rigid plastic. Keep the ideas coming!
Theatrical gels are a good starting point, but are difficult to keep flat. It is impossible to ‘stretch’ an item to remove the wrinkles when the item has no natural ‘give’ in it, in this case lighting gel.
In order to get a totally flat and equally spaced diffusion surface I would suggest a rigid material like perspex or other polymer sheet. Some are available in whites or frosts, or get clear and frost to the desired level with an orbital sander and different grades of abrasive. Remember to keep the frosted surface inside to simplify cleaning. Oil from finger prints are a right pain!
Unless your diffuser it is totally flat, your patterns will be distorted because the diffusion material is like lots of tiny lenses and the effect is proportional to distance from the light source. With a rigid sheet, you can experiment with spacing very easily before you construct the frame to get the distance just right.
Mounting is an issue. Posts cast shadows, but a frame is probably your only solution. Either channel as you have muted or cut a slot in the frame material to hold your sheet as you put the frame together. Or just screw/glue directly onto the frame. Make the back with the LEDs mounted on the removable panel for servicing.
Have you experimented with different types of diffusion materials and ways to mount the LEDs directly to the diffusion material?
Have you thought about using epoxy (possibly too messy) or silicone encapsulant to mount the LEDs directly to the diffusion material. This might minimize any shadowing.
To get different effects you could mount the leds to an acrylic or polycarbonate rod (round square or triangle) between the led and diffuser and then attach the shape to the diffusion material.
And for even more fun perhaps mount the rod or triangle on a hinge and attach a servo to move the “focus” for the diffuser.
I know a lot of grips who would take offense at that assertion! It’s not the easiest thing to do, but is is doable….there are also versions like Rosco Hilite 3014 that is more rubbery akin to a shower curtain….then there’s also the ‘silk’ material that is often used in big flying rigs, but that will get pricey…then there’s this: http://www.usplastic.com/catalog/item.aspx?itemid=23901&catid=442
Thanks for the ideas everyone! @Adam_Sharp - what you are describing is the direction I was hoping to go. Ideally I would like to go with a non-colored, frosted, rigid plastic of some kind. I have a couple of industrial plastic suppliers nearby so I have easy access to a variety of materials.
The biggest issue I ran into on a previous project was figuring out how to support the center portion of the plastic piece without the support being seen. On my first project I used a frame and that worked okay. I might do that again here. There is one thing you said though that I don’t understand. You said “channel as you have muted”. What do you mean by that?
I used this acrylic to diffuse a LED matrix. Looks black when the LEDs are off. Kinda pricey though. http://www.acrylite-shop.com/US/us/acrylite-textured-i0f0v9eylv4/acrylite-textured-black-white-9h04-sc-juy7atttk90~p.html
I had forgotten about that stuff. I stumbled across it a few weeks ago and it sounded very interesting. A 30" x 30" piece from that site is $50 which isn’t horrible. How far from the LEDs did you mount it?
It’s about 5 cm which is far enough to diffuse pretty well, note that is with diffused led pixels though. For the cost don’t forget about shipping . The site quotes me $25 for ground to New Hampshire 
You can save a few bucks with a commercial address tho.
Yep - shipping is definitely a factor. I think one of the local places has it, although I think they require you to buy an entire sheet. What I found before that I really liked was this:
The black/white stuff sounds cool too though!
@Dave_Morgan in this context (and actually it was not you, but Michael), I was combining two comments of the acrylic sheet and the aluminium channel from the top of the comments. ‘Muted’ means not expressed openly or strongly.
So I was combining all the information and forming a unspoken conclusion. Sorry, muted is not a very common term these days.
For a cheap diffused option I have used Humbrol Glass Etch which comes in a spray can. I had to do several coats but I was pleased with the effect. Another option I have just ordered is Frosted Window Film which is commonly available on Ebay. It seems to come as either a cling film type which is easily removable or a more permanent adhesive version like car window tints. I have just ordered some of the adhesive type to try it out. They also seem to do types with “ice” type patterns in the frosting.
Good to know you are making progress and discovering new materials.