Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2.5
Situational Awareness
ATC Issue All Types
Flight Crew Landed As Precaution
ATC Equipment / Nav Facility / Buildings
Low ceiling/night time conditions with aircraft reporting breaking out of the clouds at minimums. Landing runway 9L. Runway not visible from the tower. Aircraft X on rollout reported a scary incident that the lights; all the lights; on the runway turned off for 'a couple of seconds.' The aircraft had just broken out when they said they picked up the lights and then they went off and came back on before the decision to abort the approach was made. The aircraft landed and reported the incident at taxiing speed.After discussing with other controllers they have seen lights turn off and then come on almost like the generator has an overlap. Usually it happens and there is little to no overlap especially with aircraft on final in VFR weather. The pilots sounded shaken from the incident and all the aircraft after I'm sure had added workload in the actual fear of not having lights available when they broke out. In my  years [as a controller] this was one of the most serious incidents to safety of an aircraft that I have seen.When switching to and from the generator power (if that is what caused this) then a NOTAM or a request to ATC from tech ops [is recommended] as when to do this. If it was an automatic switch on then there needs to be a zero overlap system put in.
ORD Tower Controller reported a recurring problem with momentary loss of runway lights.