For making injection mould into a part with multicolor graphics molded in without using a secondary operation which eliminates cost. Critical part of this technology is the film quality and the feeder system that positions the film in the exact spot in the plastic injection mould every time. If the film has 25% bad graphics then your finished part scrap rates will be >25% etc. The film has to be 99.999% good and the feeder must put the film in the same position in the tool every time or your scrap rates will be huge.
This slows down the plastic injection moulding operation and may result in to expensive a part. I suggest you look at what your competitors are utilizing on similar products. Then make your decision based on that analysis and your requirements for your lenses appearance. I provided four processes that you will see more often than the injection mould makers option. David has provided his suggestion based on his success and I agree with the sand blasting as an alternative. As he noted - it can be repaired and once again made uniform by the injection moulder as the need arises. You can also use a chemical etch on the cavity side, using standard texturing processes. The amount of etch might in the area of MT11000 or equivalent. Whatever is used, it is highly dependent on the optical path (geometry of the part, specific led, and required amount of diffusion). Long light pipe, or plastic cap for a button, or ... There were times, when we had to add either a diffuse film on the back of the light pipe, or a milkly part. Sometimes; you can also add some TiO to the resin used to make plastic injection mould the light pipe, if it is not very long. There are lots of great EDM finishes to choose from. If you would like a free guide, contact Poco EDM in Decatur, TX, or visit their website. Most common EDM in Charmilles, so request that plaque. You might need to sneak up on it, try a real fine texture first. I did work at HP, and we used EDM and Mould-Tech or compatible texture companies. I have run a few pilot samples of Coca-cola labels onto red PC panels. Locating labels into the injection mould can be challenging if the plastic injection mould was not built for this, but the result if mastered, can be very rewarding and pleasing to your customer. Clear labels with colored text provided a good look. You may have to try a variety of thicknesses. Also, spend the extra capitol dollars for automation, unless the program is low volume.