I'm not sure this will work in your case but there is a function to change the length of time the light will stay on. Press and hold the light button on your wall control for 10 seconds. This toggles the various lengths of time. You may have a stuck relay on the logic board causing your problem.

Found out the logic board is bad. Even under 2 year warrenty, cannot get replacement part without paying for service call. Part is $95 thru Sears, service call with labor is 132, and their cost for part is $130. This opener is made by chamberlain and web price is about $75 including shipping for replacement board. Was able to renew 1 year service contract for another yr since within 3 months expiration for $39. Therefore if you can use a screw driver and disconnect plugs you can do it yourself for $200 or so less than thru sears service technician!