Method 1 - Enter the number of light bulbs in marked rows or each row (Answer key for example - 2311222)

Method 2 - Column position of left most bulb in each row (Answer key for example - BABDACB )

Depending on the specific puzzle, both methods can be applied. But, in general, I would prefer method 1 (all rows) for grid sizes up to 10. For higher grid sizes, method 1 (with marked rows) would be better.

Since the idea is to have a standard key, method 2 will be sufficient.
But maybe 123 will be easier than ABC.

Edited by Rohan Rao 2011-07-06 8:33 PM

Method 2 will not be possible as a standard key since you might have to solve the left part of some puzzles only.

I prefer method 1. Whether you have to enter marked rows or all rows does not really change the key.

Yes, the left-side of a grid might be solvable earlier. Maybe you could have entering 1 or 0 for marked row/column instead of every row (like euklid suggested).

Couldn't you mark certain black square with letters and have people enter the clue value for those ones? Generally these puzzle don't have clues in all black squares. This would ensure easier counting and you can choose the right squares by the way the puzzle is designed.
Other possibility would be marking white squares with letters and have them enter which of those letters end up with a bulb. That eliminates counting all together.