day light length

I just read in Aquarium Pflanzen, that Echinodorus sp. can be induced to 
flower by providing them with either a long day or a short day. Some species
are day length neutral and flower all the time.

Nowhere, however, can I find the definition of "day". Is a short day,
a period with less than 12 hours of illumination - and then total black-out?
Or does the night light in the corner put out enough photons to make the plant
"think" it still lit?  What about the car lights that strike the window
blinds, opposite from the tank? Does the mometary bright flash have an effect?  
If no, how long is too long?
Also, over what period do the plants need a short day before the flower?
One night? One week? Several weeks?
Sorry for all these questions, but I would really like to see my swords to
flower again and I think this is an area that hasn't received a lot of
press. :-)