I want to tell you how to make the perfect backlit that looks just as good during the day as at night when it’s lit up — that will also last years. Yeah, I thought you might be interested.
The key to an effective day/night backlit is using two printed layers. One layer is seen during the day, and at night, the light shines through two layers. Anytime you put light behind a print the inks will look washed out, but if you have two layers of ink, the image will look the same when lit and during the day. For backlits that do not need to be seen unlit (by daylight) you can use the double strike option available with some printers and RIPs. However, I do not recommend this for backlits that must be seen unlit in daytime and lit at night because the print will look too dark during daylight hours.
There’s more than one way to make a backlit, so lets review a couple of different applications so we are clear on what it is we are going to be doing.

First-surface backlit. This method works, but in my opinion, is not ideal. This can be done using translucent Lexan for the sign face and overlaid with a vinyl print. The drawback to first-surface backlits is that they won’t resist the environment as well and will be more susceptible to fading. Also, if you install the vinyl on a translucent piece of Lexan the lights will have a more difficult powering through two white layers (the white Lexan and the white vinyl film).

Second-surface backlit. I recommend this method. It requires a clear piece of sign-grade Lexan (UV coated on one side and is 3/16" thick). For this approach you will be installing the imaged film on the inside of the light box, so the Lexan will be exposed to the elements and the UV-coated side will face the sun. This application will last the longest, wear the best, and look the best. For this article we will be doing a second-surface backlit.

STEPS TO A PERFECT BACKLIT
1) Selecting the vinyl. If this sign is temporary then you need to choose a vinyl that has a removable adhesive. We will be using Avery’s translucent vinyl called MPI 2150 white translucent, and Flexcon’s Clear vinyl, along with 3M 8519 over laminate. Now, I don’t usually mix three different manufactures, but in this case all these vinyl products work together.

2) Ready the image. Backlits work best if the image has a lot of contrast. We have chosen an image from one of the past covers of Digital Graphics magazine featuring last year’s Super Bowl. We are going to print this at 30" x 40" for a 30" x 40" backlit display.

3) Printer and Ink. The printer we have chosen is the HP 9000 solvent inkjet printer. Grand Image in Hudson Mass., was kind enough to help us with the printing. Thank you Eli. The ink quality for backlit displays is the most important because the image gets sun all day and light from behind all night. Both light sources can cause ink to fade. The better the inks are, the longer the image will last — in most cases hot solvent inks will last the longest, mild solvent next and eco-solvent third.

4) Two reverse prints. We must print the vinyl as a mirror image because we will be installing the vinyl from the inside. Print the first mirror image onto the clear vinyl and the second mirror image on the translucent vinyl. If you have never done this before, print two extra copies of each in case of mishaps (I destroyed four in a row the first time I did it).

5) Laminate. Now you need to laminate the translucent vinyl with a good cast UV overlam. For this project I have chosen 3M 8519 vehicle graphics vinyl laminate.

6) Remove liner. Remove the protective liner from the Lexan, but only on side that does not have the UV coating.

7) Wet install. Wet the Lexan and the clear vinyl print and install the clear vinyl print onto the Lexan and allow to dry. (I don’t recommend doing this dry or with a laminator as you may stretch the vinyl which will cause registration problems later).

8) Install second layer. Place the Lexan and clear vinyl print onto a light table and wet the translucent vinyl and the surface of the mounted clear vinyl. With the light shining through the Lexan, line up the translucent print onto the clear print until you get perfect registration between the two prints. Be Very Careful. Misalignment here will result in a fuzzy looking backlit.

9) Install finished print. Allow to dry and then install in your light box.

What we have just created is a day/night backlit sign. During the day the light will penetrate through the Lexan and ink on the clear vinyl, and when the sun hits the translucent layer (white as it looks to you and me when the sun hits it) the sign will look just like a normal sign. But when the sun goes down and the lightbox is lit what you will have now is two layers of ink that the light is powering through and this gives you vibrant color.

(Step-by-step photos)

Here we printed a test image to see how the colors look on the vinyl. For this project we are using an HP9000 solvent-based printer to print onto vinyl. Special thanks to Grand Image
(www.grandimageinc.com), Hudson Mass., for their invaluable help with this project.

I printed two versions of the image onto both the clear and white vinyl, just in case I messed up one of them.

Here we laminated the film that will be next to the bulbs. In this case the translucent vinyl will be the closest to the bulbs, so I put 3M 8519 Luster Cast Lam onto the print.

Both mirror prints are ready to go. Before I start mounting, I put them onto the light table to make sure the prints will line up with each other.

The clear print should always be installed onto the Lexan first. Cut the Lexan to the exact size needed for the light box, then peel back the liner on the clear print.

As you can see, without the white vinyl, the image looks washed out and not very bright. This layer is just for the extra ink needed when the backlit is lit. You don’t need this to be bright as the translucent vinyl will do this for the graphic.

Here I am using application fluid to wet the surfaces before mounting. You should always install these graphics wet to avoid stretching the vinyl and to aid in getting good registration.

When installing digitally printed vinyl you should always use a squeegee that has a some kind of protection on it to prevent scratching the print. In this case we used a bit of Velcro tape.

No, we’re not done yet. I just wanted you to see for yourself that if you use only the clear vinyl, the illuminated image will look washed out. You need both layers. Let the print lay flat for a few hours while it dries before you attempt to install the translucent layer over the clear layer.

I normally use a very nice light table but if you don’t you can rig one this way. This method is not great but it will work in a pinch.

Here is what you see when you are installing the translucent vinyl onto the clear. As you can tell, you really need a good light source under the graphic to get things lined up.

Lining up the two images perfectly is important. If you do not get them dead-on, the image will be look fuzzy and not crisp. This is the most difficult part. When aligning the images, start in the center and work your way out to the edges. If you have an issue with alignment, you can use a torch to help stretch the film to force it to line up. If you keep having alignment issues, then check to make sure your printer is stepping properly.

OK, the alignment is perfect. Here is what you should see when you are done. The text should look crisp, tight and perfectly aligned.

All done. We’ve mounted the print in the light box, and here you see it in daylight. It was a snowy day here when I finished the job, so there was no direct sunlight for the shot. I used lights in my studio to light the front of the box.

Here it is with lights behind it. As you can see, the image looks vibrant and the colors are bright.