Two basic circuits of photorelay a

Photoelectric relays use photosensitive elements to convert light energy into electrical energy. Commonly used photosensitive components include photoresistors, photodiodes
, phototransistors, photovoltaic cells and photocoupler devices.
    Photoelectric relays are divided into two circuits: light-on and dark-on. Light switching means that the relay is closed when the photosensitive element is exposed to light; dark switching means that the relay is closed when
the photosensitive element is not illuminated. Two basic circuits
of     photoelectric relays