The **ALR-131-R** is a specific electronic component typically categorized as a **Photocontrol** (or NEMA-style locking-type photocell) manufactured by **TE Connectivity / ALR (Advanced Lighting Controls)**. It is designed to automatically control outdoor lighting based on ambient light levels. Below is a breakdown of its electronic composition, operation, and technical specifications. --- ### 1. Core Electronic Components The device functions through a series of integrated components designed to sense light and switch a high-voltage load. | Component | Function | | :--- | :--- | | **Cadmium Sulfide (CdS) Cell** | A light-sensitive resistor that changes resistance based on the intensity of light hitting the sensor. | | **Bimetal Thermal Switch** | A physical strip of two different metals that bends when heated by an internal resistor, opening or closing the electrical contacts. | | **Heater Resistor** | Converts electrical energy into heat when the CdS cell allows current to flow, triggering the bimetal switch. | | **MOV (Metal Oxide Varistor)** | Protects the internal circuit and the connected lamp from voltage surges and lightning strikes. | | **3-Prong NEMA Plug** | The standard physical interface (Locking Type) for electrical connection to the light fixture. | --- ### 2. Technical Specifications The "R" suffix in the part number often denotes specific ratings or regional compliance (often related to residential or standard utility use). * **Operating Voltage:** 105-130 VAC (Standard 120V North American). * **Frequency:** 50/60 Hz. * **Load Rating (Tungsten):** Typically 1000 Watts. * **Load Rating (Ballast):** Typically 1800 VA. * **Turn-on Level:** 1.5 Foot-candles (fc). * **Turn-off Ratio:** 1:4 (Turns off when light is significantly brighter than the turn-on threshold to prevent flickering). --- ### 3. How the Electronics Work The ALR-131-R utilizes a **Thermal Switching Mechanism** rather than a purely digital solid-state circuit. 1. **Daytime:** High light intensity hits the CdS cell, lowering its resistance. This allows current to flow through the internal **heater**. The heater warms the **bimetal strip**, which bends and keeps the main power contacts **open** (Light is OFF). 2. **Nighttime:** As light fades, the CdS cell resistance increases, cutting off current to the heater. The bimetal strip cools down, returns to its original shape, and snaps the contacts **closed** (Light is ON). 3. **Time Delay:** Because the bimetal must heat up or cool down, the device has a built-in time delay (usually 30–60 seconds). This prevents the light from flashing on and off due to car headlights or lightning. --- ### 4. Physical Features * **Housing:** UV-stabilized polypropylene cover to protect internal electronics from sunlight and rain. * **Connection:** Twist-lock (ANSI C136.10 compliant). * **Fail-Safe:** Most units are designed to fail in the "ON" position so that if the sensor breaks, the area remains lit for safety. ---