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Direct factory export catalog supporting fine particle dispersion, precision ceramic milling, and optoelectronic structural components.
An in-depth analysis of photon absorption, bandgap carrier generation, and photo-resistive characteristics in modern passive light sensors.
A Light Dependent Resistor (LDR), colloquially known as a photoresistor or photocell, is a light-sensitive passive electronic component whose resistance decreases non-linearly as ambient light intensity increases. The operational foundation of an LDR rests upon the phenomenon of intrinsic photo-conductivity within semiconductor materials, primarily Cadmium Sulfide (CdS) and Cadmium Selenide (CdSe).
In dark conditions, a CdS semiconductor crystal possesses a high electrical resistivity ($\rho \ge 10^8 \ \Omega\cdot\text{cm}$) because electrons in the material are bound within the valence band. The bandgap energy ($E_g$) of pure Cadmium Sulfide is approximately 2.42 eV at 300 K. When incident photons possessing energy equal to or greater than the bandgap ($h\nu \ge E_g$) strike the ceramic-mounted CdS film, bound electrons absorb photon energy and jump across the forbidden gap into the conduction band.
This optical excitation creates free electron-hole pairs. The electrical conductivity ($\sigma$) of the semiconductor film rises proportionally to the free carrier density according to the fundamental transport equation:
where e is the elementary charge, n and p represent electron and hole concentrations, and μe, μh represent carrier mobilities. Under intense illumination (e.g., 100 Lux daylight), carrier concentration surges exponentially, dropping the terminal resistance from megaohms down to several hundred ohms.
One of the primary engineering advantages of CdS photoresistors over silicon photodiodes is their natural spectral response alignment with the human eye visual luminosity curve, $V(\lambda)$. The peak spectral response of an industrial CdS LDR ranges between 510 nm and 560 nm, matching the green-yellow region of the visible light spectrum. This makes LDRs ideal for dusk-to-dawn lighting control systems without requiring expensive optical IR/UV blocking filters.
| LDR Model Series | Sensor Diameter | Max Voltage (VDC) | Max Power (mW) | Spectral Peak (nm) | Light Resistance (10 Lux) | Dark Resistance (10s Min) | Gamma (γ) Value (10-100 Lux) |
|---|---|---|---|---|---|---|---|
| LDR-5506 | 5 mm Epoxy Encapsulated | 150 VDC | 100 mW | 540 nm | 2.0 – 6.0 kΩ | 0.5 MΩ | 0.60 ± 0.05 |
| LDR-5516 | 5 mm Epoxy Encapsulated | 150 VDC | 100 mW | 540 nm | 5.0 – 10.0 kΩ | 1.0 MΩ | 0.70 ± 0.05 |
| LDR-5528 | 5 mm Epoxy Encapsulated | 150 VDC | 100 mW | 540 nm | 10.0 – 20.0 kΩ | 2.0 MΩ | 0.75 ± 0.05 |
| LDR-5537 | 5 mm Epoxy Encapsulated | 150 VDC | 100 mW | 540 nm | 20.0 – 50.0 kΩ | 5.0 MΩ | 0.80 ± 0.05 |
| LDR-12537 | 12 mm Industrial Grade | 250 VDC | 250 mW | 560 nm | 8.0 – 20.0 kΩ | 5.0 MΩ | 0.85 ± 0.05 |
| LDR-20539 | 20 mm High-Power Glass/Metal | 500 VDC | 500 mW | 560 nm | 5.0 – 15.0 kΩ | 10.0 MΩ | 0.90 ± 0.05 |
Why Tier-1 buyers and OEM system integrators partner with our specialized semiconductor manufacturing facilities.
Our automated chemical vapor deposition and ceramic sintering achieve ultra-tight gamma tolerances (±0.05), ensuring identical sensitivity curves across millions of mass-produced sensors.
We supply moisture-proof anti-UV epoxy dip formulations and glass-to-metal hermetic TO-cans rated to IP67, enabling decades of reliable outdoor deployment without drift.
Capable of direct AC load switching through solid-state relays or triacs. Heavy-duty 12mm and 20mm series handle up to 500mW power dissipation safely at elevated ambient temperatures.
How localized raw material refining, automated dipping lines, and cluster synergies drive unmatchable price-to-performance metrics for international markets.
The global optoelectronic landscape relies heavily on China’s mature industrial clusters located across Jiangxi, Zhejiang, and Guangdong provinces. As a premier wholesale manufacturer and exporter, our production ecosystem integrates raw material purifying (cadmium and sulfur synthesis to 99.999% purity), ceramic substrate slicing, micro-screen printing, and automated testing under a single quality control standard.
Traditional photoresistor manufacturing suffered from batch variation due to manual dipping processes. Our state-of-the-art facilities utilize fully automated robotic dipping lines that control epoxy film thickness down to ±0.02 mm. Sintering takes place in computer-controlled atmosphere furnaces with multi-zone thermal profiling, ensuring standard chemical stoichiometry across every single CdS chip.
Every single LDR component passing through our assembly lines undergoes 100% automated 10-Lux flash testing. High-speed spectrophotometers and digital ohmmeters categorize photocells into precise resistance bins within milliseconds. This eliminates out-of-spec parts before packaging, enabling global OEMs to incorporate our components directly into automated SMT and lead-insertion production lines without incoming inspection failures.
From smart city lighting controls to industrial combustion safety, discover where our light-dependent resistors deliver mission-critical reliability.
Integrated into ANSI C136.10 NEMA twist-lock receptacles and Zhaga Book 18 photocontrol sockets for automatic dusk-to-dawn municipal luminaire switching.
High-voltage 20mm glass-encapsulated LDRs detect yellow oil flames in commercial boilers and gas burners, triggering instant fuel shutoff in case of flameout.
Arranged in differential quadrant pairs, precise gamma-matched LDR sensors align solar PV panels toward maximum solar irradiance throughout the day.
Navigating international hazardous material regulations, custom packaging options, and logistics support for global importers.
Because Cadmium (Cd) is listed under EU Directive 2011/65/EU (RoHS 2) as a restricted heavy metal, B2B procurement teams must verify compliance paths. Photoresistors for analog optocouplers and professional safety applications utilize RoHS Exemption 8(b) (“Cadmium in photoresistors for analog optocouplers applied in professional audio equipment and safety applications”).
For markets requiring completely lead-free and cadmium-free solutions, our engineering division manufactures drop-in alternative Ambient Light Sensor (ALS) Phototransistors housed in standard T-1¾ (5mm) epoxy packages that replicate the logarithmic output curve of CdS photocells without heavy metal usage.
Our manufacturing complex operates strictly under ISO 9001:2015 quality management system and ISO 14001:2015 environmental standards. For global B2B buyers, we offer flexible tape-and-reel (Ammo Pack) packaging optimized for automatic insertion equipment, as well as bulk anti-static vacuum-sealed bags with desiccants for extended shelf life.
Clear, direct answers regarding photoresistor selection, circuit design, custom specifications, and international export logistics.
γ = [log(R10) - log(R100)] / [log(100) - log(10)] = log(R10 / R100)
Explore our complete export line of Silicon Nitride (Si3N4) bearing balls, ceramic column packing, and high-purity microcrystalline media.
