What is a light sensor? Six indicators of light sensors

A light sensor is a device that converts an optical signal into an electrical signal and is a type of sensor. The most commonly used light sensor should be a light-controlled switch. The core component is a photoresistor, which changes the resistance value due to the change of light intensity, which causes the current to change, so that the optical signal is converted into an electrical signal.

When choosing a light sensor, the most important point is to understand which specification parameters are the most critical. In general, when selecting a light sensor, the important factors to be considered include spectral response/IR suppression, maximum lux count, photosensitivity, integrated signal conditioning, power consumption, and package size. The specific description of these six specifications is as follows:

1. Spectral Response / IR Suppression: The ambient light sensor should only be sensitive to the range of the 400 nm to 700 nm spectrum.

2, the maximum number of lux: most applications are 10,000 lux.

3. Photosensitivity: According to the lens category of the light sensor, after the light passes through the lens, the light attenuation can be between 25[[%]]-50[[%]]. Low sensitivity is critical (5 lux) and you must choose a light sensor that can operate within this range.

4. Integrated signal conditioning functions (ie amplifiers and ADCs): Some sensors may provide a very small package, but require an external amplifier or passive component to obtain the desired output signal. Optical sensors with higher integration eliminate the need for external components (ADCs, amplifiers, resistors, capacitors, etc.) and have additional advantages.

5, power consumption: For optical sensors to withstand high lux ("10,000 lux", it is best to use non-linear analog output or digital output. 6, package size: For most applications, the package is as small as possible. The smaller package sizes available today are approximately 2.0mm & TImes; 2.1mm. The 4-pin package measures 1.3mm & TImes; 1.5mm is the next generation package. Applications of light sensors in automobiles range from portable consumer markets (smart phones, PDAs, desktops, portable music players, etc.) to consumer TV markets (TFT-LCD, plasma, tail projection, CRT, etc.) In the medical, industrial and automotive markets, light sensors are ubiquitous displacement sensors.

In the automotive environment, the main applications are as follows: car entertainment / navigation / DVD system backlight control, in order to display the ideal backlight brightness under all ambient light conditions; rear seat entertainment display backlight control; instrument group backlight control ( Speedometer / tachometer); automatic mirror brightness control (usually requires two sensors, one is forward, one is backward); automatic headlights and rain sensing control (dedicated, change according to demand); Rear view camera control (dedicated, changing as needed) load cell.

Light sensors have become one of the most effective solutions for providing more comfortable display quality. They have characteristics similar to those of the human eye, which is critical for automotive applications because they require all ambient light conditions. Can achieve a full backlight effect. For example, during the day, the user needs maximum brightness to achieve optimal visibility, but this brightness is too bright for nighttime conditions, so a light sensor with good spectral response (good IR attenuation), appropriate The dynamic range and overall good output signal conditioning make it easy to automate these applications. Now the end user can set several threshold levels (such as low, medium, and bright), or be able to dynamically change the backlight brightness of the sensor. Pressure sensor is also suitable for car rearview brightness control when the mirror is darkened and/or changed. Intelligent brightness management is required when lighting, and the angle sensor can be done with an ambient light sensor. The latest trend in the optical sensor market is that the light sensors in small packages are versatile and affordable. Passive devices have been active in the market for decades, and as photoresistors, photodiodes, and phototransistors become more common and cheaper, they are widely used in many consumer products ranging from nighttime lights to digital cameras. The soon-to-be integrated device integrates a phototransistor or photodiode with a current amplifier for on-chip calibration, filtering, and higher resolution. When the resolution is high, functions such as low light power and power supply suppression are exerted, and such devices are expanding the application range and effectiveness of the ambient light sensor.

The simplest light sensor is a photoresistor that can be identified by a channel between two terminals. The low-end version is made using CdS (cadmium sulfide), while the more expensive type is made using GaAs. GaAs has a small band gap that allows it to absorb low-energy photons in infrared light, allowing electrons to transition to the conduction band. The reference component data shows that the illumination range is from 1 to 100 lux, but with various resistance values.

ISL29001 can achieve 15bit resolution.

The application of light sensors is very common. Some applications use optically detected reflected light to sense position, including bar code readers, laser printers, and autofocus microscopes. Applications such as portable electronic products such as digital cameras, mobile phones, and notebook computers use light sensors to measure ambient light. We will discuss further the second type of application above.

An ambient light sensor in a laptop that adjusts the backlight of the screen to the level of comfort. The comfort range of the backlight depends on the light of the room. It is conceivable that the brightness of the screen needs to increase with the brightness of the ambient light. In the case of weak light, the screen brightness needs to be lowered in order to look comfortable and extend the battery life. .

In notebook design, the ambient light sensor is usually next to the speaker, not on it, and the machine has an opening in the speaker position where light can enter the interior. These audio ports are usually covered with a mesh to protect the speakers. Due to this protection, the light is blocked, which reduces the amount of measurable light, so a solution with good dark precision is required. In order to achieve the accuracy required in low light conditions, it is best to choose an integrated photodiode with an ADC. At the same time, high-pass filters can be used to minimize power supply noise and prevent it from coupling into backlighting. Another common application is ambient light sensing in mobile phones. In this application, each saving of one milliamp means an increase in battery life and an increase in customer satisfaction. Using a light sensor to adjust backlighting, battery life is extended by at least 6 times (assuming the backlight remains at full power without photosensor feedback).