By Joe Smith, Texas Advanced Optoelectronic Solutions

The ability for a display to sense ambient light could be a powerful tool that can lead to increased power efficiency and customer satisfaction. This application note will discuss some of the benefits of implementing ambient light sensing as well as some considerations to keep in mind during the design.

WHAT IS ALS
Simply stated, ambient light sensing is the ability to measure the brightness of light incident on a surface. It is often useful to utilize this brightness information to control certain aspects of a system, such as the brightness of a display, or the size of an aperture. End products that can benefit from ALS implementation include laptops, monitors, cell phones, televisions, digital signage, cameras and any device with a visual user interface.

WHY ALS
There are two important drivers of ALS. The first is the added power management control that ALS affords a system. Display backlighting typically constitutes a large share of a systems power resources. It is common for a laptop PC display to consume between 30% and 40% of the total power budget. Substantial power savings can be realized when the brightness of a display is effectively controlled by ambient light.

A secondary ALS benefit is the improved visual experience to the user. Regulating system lighting based on ambient conditions in essence allows for the system to anticipate and act upon the needs of the user. This could be achieved by increasing display brightness in a bright setting or enabling system lights in a dark setting.

MEASURING LIGHT
To fully understand how to measure light, it is necessary to first discuss the units of light measurement and how they differ. Light is electromagnetic radiation that the human eye is sensitive to. Electromagnetic radiation can be characterized by its strength and how its energy is spectrally distributed. The human eye responds to energy with wavelengths between about 380 and 780nm, with a peak around 555nm (figure 1). This is called photopic response.

For details, open the attached file.