Light Activated Silicon Controlled Rectifier (LASCR) are light activated thyristors (SCR), Light Activated SCRs also known as Light Triggered Thyristor
(LTT). Once the light falling on the rectifier exceeds a certain threshold, the LASCR allows the current
topass in one direction.brightness of the incident light falls below a threshold value, the LASCR blocks the flow of current. LASCRs have the highest sensitivity when the gate is open. In addition, LASCRs can be triggered with a pulse on the gate and then operate comparable to conventional thyristors (SCR). LASCRs are used in light-controlled devices and twilight switches.