Some kind of plastic needed

[martin54]

If you know where you can get lots of vinyl off cuts then ask them if they have any translucent off cuts or even frosted you can try. Translucent is what is used for lightboxes so allows more light through & frosted is available in different colours & will also allow more light through. Both have a matt finish which will help with the glare.
Don't know if these get moved about a lot but if you go down the sheet material route then polycarbonate might be a better option than acrylic, acrylic tends to be a bit brittle but make sure it is an exterior grade. Exterior grade is UV stabalised which stops it yellowing over time.

Another option if you are still experimenting & still have units to manufacture is to change the colour of the LEDs so they show up better during daylight hours.