You have a short which is tripping the circuit breaker in the light switch. After a few seconds, the breaker will reset itself and flash the lights momentarily if you leave the switch turned on. Check the dimmer switch- - - -it's been a chronic source of short circuits for the 50-something years I've been doing electrical work.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!