How Photocells Work
The magic of a photocell lies in a tiny component called a photoresistor, which changes its electrical resistance based on the amount of ambient light it detects.
- At Dusk: As the sun sets and the natural light level falls below a certain threshold, the sensor’s resistance increases. This change triggers an internal switch, closing the electrical circuit and turning the connected lights ON.
- At Dawn: When the sun rises in the morning, the sensor is exposed to light again. Its resistance drops significantly, which causes the switch to open the circuit, turning the lights OFF.
This automated cycle ensures lights only run when needed, dramatically reducing energy consumption and extending the lifespan of your bulbs.
Types of Photocells
Photocells are available in a variety of shapes and mounting styles to suit any fixture or application.
- Button Photocells: Small, discreet, and among the most common types. Designed to mount directly onto an outdoor light fixture or junction box through a small drilled hole for a clean, integrated look.
- Swivel Mount Photocells: Featuring an adjustable arm, these sensors can be aimed with precision toward open sky, avoiding interference from artificial lights that could cause premature shutoff.
- In-Wall Switch Photocells: Combines a photocell with a standard wall switch, replacing a regular switch indoors to control an entire circuit of outdoor lights — often with a manual override for convenience.
- Plug-In Photocells: The easiest option for temporary or decorative lighting. This portable adapter plugs into any outdoor outlet for instant dusk-to-dawn automation of string lights or holiday displays.
Advanced Control: Dimming and Daylight Harvesting
Beyond simple on/off functionality, advanced photocells are used in commercial and energy-efficient buildings for a strategy called “daylight harvesting.”
- Dimming Control Photocells: Rather than acting as a switch, a dimming photocell acts as a throttle — providing a variable 0-10V signal to a dimmable LED driver or ballast. More daylight results in a lower signal and dimmer lights; less daylight results in a higher signal and brighter lights.
- Daylight Harvesting: The practical application of dimming photocells, maintaining a consistent optimal light level by supplementing natural light with precisely the amount of artificial light needed. This can reduce a building’s lighting energy consumption by 20–60%.
Common Applications
Photocells are the standard for automated control across a wide range of outdoor lighting scenarios.
- Security & Area Lighting: For floodlights, wall packs, and barn lights around residential or commercial buildings.
- Landscape & Accent Lighting: To automatically illuminate pathways, gardens, and architectural features.
- Entryway Lighting: Perfect for porch lights, post lanterns, and garage sconces.
- Commercial & Municipal Lighting: The primary control method for streetlights, parking lot lights, and building exteriors.
Shop Photocell Sensors at Bees Lighting
A photocell sensor is a cost-effective and dependable way to ensure your property stays safe, secure, and welcoming after dark — with no manual switching or complex programming required. Browse the full range of dusk-to-dawn and daylight harvesting photocell sensors at Bees Lighting, or explore the complete lighting controls collection including timer switches and motion sensor light switches.
