A light sensor, as its name suggests, is a device that is used to detect light. There are many different types of light sensors, each of which works in a slightly different way. A photocell or photoresistor, for example, is a small sensor that changes its resistance when light shines on it; they are used in many consumer products to determine the intensity of light. A charged coupled device (CCD) transports electrically charged signals, and is used as a light sensor in digital cameras and night-vision devices. Photomultipliers detect light and multiply it.
Devices that include these sensors have many uses in scientific applications, but are also found in items that people encounter each day. A simple light sensor may be part of a security or safety device, such as a burglar alarm or garage door opener. These types of devices often work by shining a beam of light from one sensor to another; if the light is interrupted, an alarm sounds or the garage door won't close.
Many modern electronics, such as computers, wireless phones, and televisions, use ambient light sensors to automatically control the brightness of a screen, especially in low-light or high-light situations. They can detect how much light is in a room and raise or lower the brightness to a more comfortable level for the user. Light sensors also may be used to automatically turn on lights inside or outside a home or business at dark.
Barcode scanners found in most retailer locations work using light sensor technology. The light emitted from the scanner illuminates the barcode, which is read and decoded by a sensor. Quick Response (QR) codes operate in much the same way, though they contain more information and typically can be read using a smartphone if the user has downloaded a code reader.
While some products that use light sensors have been around for a number of years, these sensors continue to become more important, especially through infrared technology. Warm-blooded animals, including humans, emit heat, which can be seen as infrared light. This energy can be detected using infrared light sensors to tell when a person is walking by, as opposed to being activated by another, non-human movement.
Motion-activated light sensors that recognize infrared can be found in grocery stores, for example. When a shopper walks by, the sensor in a display case recognizes that a person is passing, and the lights are turned on. The lights dim when no customer is in front of the case, and the store saves on energy costs. Many retailers and businesses use similar technology to control lights in rooms that are not in constant use, such as conference rooms or restrooms.
Light sensors continue to have many uses in science, from the simplest science fair experiments to the latest breakthroughs in space, medicine, and robotics. Robots, for example, can use light sensors to "see" and navigate around a room, detecting objects by sensing how light bounces off them. Improvements in fiber-optics technology will likely bring even more breakthroughs, as this technology can measure light and send signals in extreme conditions or remote locations where electricity isn't available.