Dayjillymo said:OK - I'm gong to show off my ignorance here. . . but how does a light box help with seed sorting?? Maybe I'm working way too hard! 
Backlighting only works with certain seeds. The method is actually a learned process, and although the theory is simple, it's not always as intuitive as one might hope.
---- The basic part is that a backlight allows one to see through (some) seeds, so you can see if "anything" is inside.
---- The hard part can be the interpreting of what you are seeing (or not seeing). But the goal is to be able to more easily remove chaff from real seed and determine if seeds are viable or not.
Seeds of the
Lilium genus are probably the most commonly candled seeds. ("Candling" is the name of this process that determines viability through the use of backlighting.)
Without backlighting, they look like, well, just seeds. One assumes they are all good, but you really don't know for sure.
But put a back light to them (or have a candle behind them), and you can see the parts of the seed, including an embryo (if it is present).
