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A light-dependent resistor (LDR), also called a photoresistor or photoconductive cell, is a passive semiconductor component whose electrical resistance changes with the amount of light it receives. In the usual LDR behavior, more light means lower resistance; less light means higher resistance. This makes an LDR useful for detecting a change from light to dark, though a basic LDR circuit is not automatically a precise light meter.
How does a light-dependent resistor work?
An LDR is photoconductive: when light is absorbed by its photosensitive semiconductor, charge carriers become available to conduct electricity. The material conducts more readily, so the component’s resistance falls as illumination rises. The exact characteristics depend on the specific part.
CdS, or cadmium sulfide, photoresistors are one documented type, not a material that should be assumed for every LDR. Token Components describes a CdS photoresistor with an active semiconductor layer on an insulating substrate. Check the chosen component’s datasheet for its material, spectral response, resistance range and electrical limits: Token Components: Photoresistor, CdS, Light Dependent Resistor LDR.
What does an LDR do in a circuit?
An LDR converts a change in light into a change in resistance. A common way to turn that resistance change into a measurable voltage is to pair the LDR with a fixed resistor in a voltage divider. The voltage at the divider’s midpoint depends on the two resistance values and their placement, so its direction of change is not fixed: putting the LDR on the supply side gives a different result from putting it on the ground side. Analog Devices discusses this circuit approach and the importance of the physical setup for ambient-light applications: Simple Ambient Light Sensor Circuit.
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- 100pcs 5528 Light Dependent Resistor
With suitable circuit logic, the changing voltage can be used to respond to bright or dark conditions. For instance, a circuit can be arranged to switch a light on when illumination drops below a chosen level. The LDR itself does not make that decision; the surrounding circuit determines how its resistance change is used.
How is an LDR different from other light sensors?
“Light sensor” is a broad category, not another name for an LDR. Photoresistors, photodiodes, phototransistors and photovoltaic cells differ in how they respond to light and what they provide to a circuit. Analog Devices distinguishes these sensor types and their operating mechanisms in its Light Sensor overview.
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- Quantity: 30 x photoresistor, 5 mm GM5539 resistor
- Maximum voltage: 150 Volt DC
- Maximum wattage: 100 mW; Spectral peak: 540 nm
- Light resistance (10 Lux): 50-100 Kohm; Operating temperature: - 30 ~ + 70 degree Celsius
- Enough photo light sensitive resistors are handy for your DIY and hand working projects
- LDR or photoresistor: Light changes the component’s resistance through photoconductivity.
- Photodiode: Uses a light-sensitive semiconductor junction to produce a current response.
- Phototransistor: Uses light to control transistor-like current.
- Photovoltaic cell: Produces voltage and current through the photovoltaic effect.
These are different mechanisms, not interchangeable labels. The right choice depends on the application’s required response, spectral sensitivity, output or resistance range, and circuit interface.
Can an LDR measure light precisely?
Do not assume that an unspecified LDR provides accurate lux readings. Parts can vary, and a resistance change alone is not a calibrated measurement of illuminance. For a particular component, consult its datasheet and calibrate the complete setup under the lighting conditions in which it will be used. Analog Devices notes that the physical setup and calibration can matter in an ambient-light circuit; Adafruit also discusses photocell variability and limitations for precise light measurement in its Photocells overview.
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- Maximum Voltage: 150 VDC
- Maximum Wattage: 100 mW
- Operating Temperature: - 30 ~ + 70 ℃
- Spectral Peak: 540 nm
- Light resistance (10 Lux): 50-100 KΩ
When selecting a component, compare its spectral response, usable resistance range and electrical limits with the circuit’s needs. Also consider how quickly it must respond and whether the application needs a simple light-versus-dark trigger or a calibrated light measurement. A model’s specifications should not be generalized to all LDRs.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When should you use an LDR?
An LDR is a straightforward option when a circuit needs to react to changing ambient light, such as distinguishing brighter from darker conditions. If the project instead needs a defined measurement range, a particular spectral response or a repeatable lux reading, evaluate the candidate sensor and its datasheet against those requirements rather than choosing by the LDR label alone.
Quick Recap
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- ☀ [What You Get]: What you will get is a 210pcs photoresistor kit. It includes 5mm photo light sensitive resistor GM5506 5516 5528 5537 5537-2 5539 5549, each for 30pcs. They are placed in a clean transparent box, and each type of photoresistor is placed separately and labeled to help you distinguish.
- ☀ [High Sensitivity]: The resistance value of the photoresistor decreases as the intensity of the incident light increases. Light-dependent resistors are made of cadmium sulfide have extremely high light sensitivity, and the response time of all models is less than or equal to 30ms.
- ☀ [Easy to Use]: The width of the photo light sensitive is 5mm, which is very small and can be installed in almost any related project. They can be used with Arduino to facilitate your measurement.
- ☀ [Good Reliability]: The resistor is coated with epoxy, which has good reliability and can serve you for a long time. It can work normally in an environment of -30 to 70 Celsius (-22 to 158 degree). It should be noted that please try to avoid direct sunlight.
- ☀ [Widely Application]: These resistors can be used for photoelectric control, camera automatic metering, children's electronic toys and circuit experiments. Many users use it as a substitute for solar lights, which can save you a lot of money.
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- High Sensitivity: The 5528 Light Dependent Resistor (LDR) features a high sensitivity to light, allowing it to accurately detect even the slightest changes in light intensity.
- Wide Range of Applications: This photoresistor is widely used in various electronic projects, such as light detection, automatic control, and light-sensitive alarms. It is compatible with Arduino and other microcontrollers, making it easy to integrate into your projects.
- Durable and Reliable: Made with high-quality materials, this LDR has a maximum voltage of 150 VDC and can withstand operating temperatures ranging from -30°C to +70°C. It also has a response time of 20ms (rise) and 30ms (down), ensuring quick and accurate light detection.
- Versatile Resistance Range: With a light resistance of 10-20 Kohm at 10 Lux and a dark resistance of 1 Mohm, this photoresistor offers a wide range of resistance values, allowing for precise control and measurement of light intensity.
- Explosive 5MM Photoresistor: This pack includes 100pcs of the 5528 Light Dependent Resistor, providing you with ample supply for your various projects. Whether you are a hobbyist or a professional, this bulk pack ensures that you always have enough photoresistors on hand.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
