Definition
A semiconductor switching device, similar to a silicon controlled rectifier (SCR), that is turned on by light striking its sensitive junction rather than by an electrical signal applied to a gate terminal. Once triggered by light of sufficient intensity, it conducts current in one direction and continues conducting until the current through it is interrupted or drops below a holding value.
Plain English
A small electronic part that acts like a one-way switch. It stays off until light shines on it, then it turns on and lets electricity flow. It keeps flowing until the electricity is cut off.
Context Anchor
Seen in aircraft electrical and electronic system discussions, especially in circuits where a light signal is used to turn something on while keeping the control signal electrically separate.
Derivation
The name describes the part directly: 'light-activated' (turned on by light), 'silicon' (the semiconductor material), 'controlled' (it can be switched), and 'rectifier' (a device that allows current to flow in only one direction). Rectifier comes from the Latin rectus, meaning 'straight' -- it 'straightens' alternating current into one-way current.
Why Pilots Care
Pilots do not normally operate this part directly, but understanding the term helps when reading about aircraft electrical systems, maintenance descriptions, or fault reports involving electronic switching.
Intuition Check
Do not read “light-activated” as meaning the device simply detects light and reports it. Here, the light actually triggers the device to switch on and carry current.
Example Sentence 1
The technician replaced a faulty light-activated silicon controlled rectifier in the optical isolator circuit during avionics troubleshooting.
Example Sentence 2
During the night preflight, the circuit containing the light-activated silicon controlled rectifier responded to the position light and completed the warning path.