Counter to darkness spell?

[Ewierl]

B0rsuk said:
Yyyes, all we need are 'Whoracle casts Darkness' 'Burunduk casts Light' 'Whoracle casts Darkness' 'Burunduk casts Light' 'Whoracle casts Darkness' style deadlocks.
Fun.

A better solution would be to have the counter be a 'Grant Darkvision' spell. If it only affects a small number of troops at a time, or only grants partial darkvision, it seems properly balanced to counter a darkness strategy without entirely eliminating its value.