[sangnoir]

LED brightness is controlled by pulse-width modulation: at low frequencies, the camera LED would appear dimly lit. A more sophisticated approach might be to combine gaze detection to ramp-down frequency if someone is looking towards the camera/LED.

[kickopotomus]

PWM reduces average power. If the LED is on the same circuit as the camera, I don't know how successful you will be at powering the camera while trying to dim the LED.

[kevin_thibedeau]

A momentary flicker would not be perceptible in a lit room.

[ljm]

A momentary click on a phone line was also imperceptible... until it wasn’t.

You might not even see the flicker but if you catch it in your peripheral vision often enough, or you found out someone else was caught by it or it hit the news big time, you’d suddenly become more suspicious about that momentary flash. Maybe even paranoid.