Depends on the voltage source 120 volt or low voltage. Low voltage lights have a transformer that might be breaking down. A 120 volt source may be arcing at a connection somewhere until it finally "makes". If you have a junction box near the light you may be able to monitor the voltage there. Fluctuations may not occur if the power source does not have a load on it. Some LED lights have internal power supplies. This may be going bad. Maybe the switch is arcing.