(Quoted from Sign & Digital Graphics. Full Article here)
In general, backlit images are meant to be viewed only when a light source is behind the image. Occasionally, however you may need to create a backlit image that can be viewed when face-lit with natural light in the daytime, and also at night when the image is illuminated from behind. The problem is that a print that looks good when backlit needs to be have a heavy ink load. It needs to be dark and dense to compensate for strong backlighting. But that same print will look terrible in a front-lit application. Here are some tips to get around the problem:
Click here to read the full article from SIgn & Digital Graphics