Hi Vicki et al
One rule of thumb for the thousands of bulb species in cultivation would be too wonderful but our germination results improved dramatically since we started leaving the seed of "difficult" species uncovered for a variable period. Now this is the routine procedure for perennials, bulbs, climbers, vegetables, you name it, for us.
Darkness as such is not very common for a germinating seed in Nature except as shelter (or competition) from neighboring vegetation.
Regards
Alberto