With more than ever electronic products available today and accessible by consumers, Ambient Light Sensors have become an indispensable component for a variety of design needs. Poor environmental lighting or changing lighting conditions while viewing television, continuous working on laptops or PCs, playing around with headsets or driving an automobile can bring significant eye strain. Designers address this problem by utilising the good human eye spectral matching property of ambient light sensor, which means that they can be used to detect light or brightness in a similar way as the human eye. This makes ambient light sensors inevitable in display dimming or adjusting LCD and OLED backlight intensity in a variety of portable devices. Not only it brings optimum viewing comfort to the user in changing environmental lighting but also helps to reduce power consumption and extend battery life.
To design a control system based on ambient light sensors, it’s fairly important to know how this sensor works. With one or multiple photodiodes or phototransistors, an ALS detects the amount of light available or the intensity of light by converting light energy into an electrical signal. Next it signals a processor so that it can determine the amount of backlight or illumination needed in an application. The processor can then dim or control a lighting control system using a PWM signal, whose duty cycle determines the resultant brightness.
Today, ambient light sensing is heading in a digital direction. Analog ALSs are still good fits for some designs, for instance, some low-end designs where price is a dominating feature. Newer digital ALSs integrate ADCs to convert the photocurrent to a digital signal for the processor. Commonly, both analog and digital versions of ALSs have a shutdown or sleep mode during which the sensor operates at very low currents to allow battery-operation in portable devices such as smartphones. Newer versions pack other interesting features such as detection as close as possible to what a human eye would detect. A wide-range ALS is capable to perform accurate measurements in lighting environments ranging from low-light to bright sunlights in many applications.
Mentioned below are reference design utilizing “Ambient Light sensors” for brightness control of displays along with complete documentation:-
- Backlight and Smart Lighting Control by ALS and Proximity sensor: This design based on ALS and proximity sensor is intended to measure and react to changes in the lighting environment to conserve power and extend backlight life using an ambient light sensor. The optical light sensor OPT3001 comes with good human eye spectral matching to dynamically adjust the backlight brightness and produce an optimal viewing experience for the user. This is done by implementing a simple relationship between backlight brightness and ambient light in software. Proximity wake up by a capacitive sensor is enabled by a capacitive-to-digital converter FDC1004 from TI to save even more power. This feature can detect if a human is close and wakes up the system. The design includes hardware files, firmware, demo, and Getting Started Guide. More on this Reference Design
- Compact IO-Link Light Sensor Design: This reference design discusses the world’s smallest IO-Link light sensor with a range of applications spanning process control, automatic display brightness, industrial automation, and more. Many sensors are integrated on-board: ambient light (clear), red, green, blue, infrared, and temperature all on a tiny printed circuit board (PCB) that is 6.5mm x 25mm. The design consists of an industry standard Maxim Integrated IO-Link device transceiver (MAX14821), a Renesas ultra-low-power, 16-bit microcontroller (RL78) utilizing TMG TE’s IO-Link device stack and a Maxim Integrated light sensor (MAX44008). The design is able to communicate with IO-link, a serial communication protocol used for communicating with sensors and actuators. More on this Reference Design
- Ambient Light Sensor Opto-mechanical Design: This design provides valuable optical/mechanical guidelines for the ambient light sensor from Intersil used for applications such as mobile consumer products with back-lit flat displays. Insights for best performance for Intersil’s Ambient Light Sensor ISL29023 using its opto-mechanical reference model are discussed. The model consists of the ISL29023 IC package mounted to a PC board (typically, a Flex-PCB) spaced 3.0mm below a 0.7mm – thick glass Window. More on this Reference Design
- NFC Temperature and Light Sensor Design: This reference design provides a platform to perform thermistor and photo transistor measurements, and communicate them to an NFC enabled smart phone or other NFC/RFID Reader device. Based on the RF430FRL152H NFC sensor interface transponder, this reference design can be operated with a battery for data logging into FRAM or without a battery utilizing energy harvested from the RF field. Boosterpack headers are available to interface additional sensors or MCU. This design has been tested and includes an application report, schematic/PCB design files and software. More on this Reference Design