My son got an eeg where they put probes on his head while he slept for 30min. do the probes have lights on them and flash when something happens?

No: The probes sense electrical activity, impulses, from the brain.

Normal stimulation: Bright lights flashing at different frequencies are used as a standard part of the eeg. Referred to as "photic stimulation, " the flashes cause discharges in the visual region of the brain. In some patients, the evoked responses are asymmetric or excessively large, which can indicate an abnormality.