Apple Wins a Patent for Luminescence Shock Avoidance in iOS Displays

The convenience of today's handheld portable devices combined with their ever-increasing multi-media functionality has made such devices seemingly ubiquitous, with users carrying them everywhere, in purses or clipped to belts. To a dedicated user, these personal devices could be as indispensable as a wallet. To that end, users may place these personal devices within arms-reach wherever they go, including vehicles, movie theaters, and the like.

Because personal devices tend to have small batteries, power savings is critical. A large display illuminated to full brightness will exhaust a battery in no time, and thus power saving functions such as sleep modes are common in personal devices.

For example, the display of a mobile telephone may be dimmed or go dark altogether until a call is received, or the screen of a PDA may go blank until the user activates a function or a communication such as an e-mail or text message is received. However, if one of these personal devices is in a sleep mode in a dark environment and the display is suddenly illuminated due to a received call or other communication, a nearby user who happens to be looking at the device or is instinctively drawn to looking at the display when it illuminates could suffer temporary vision impairment. Because the user's pupils have opened up in the dark environment, the sudden flash of light could cause short-term blindness or at least impaired vision. This temporary impaired vision could range from a mere annoyance to a life-threatening situation if the user is driving a motor vehicle.

Apple's Solution

Apple's invention focuses on a luminescence shock avoidance algorithm. According to Apple, a luminescence shock avoidance algorithm could be employed to selectively limit the brightness level of a display device when the display device is activated in a dark environment to prevent the temporary vision impairment that could occur when a display device is activated in a dark environment.

The algorithm receives the state of the display (e.g. on or in standby mode), and could optionally receive an ambient lighting value from an ambient light sensor and a user-selectable manual brightness adjustment setting to determine whether luminescence shock avoidance should even be triggered, and if it is triggered, how much should the brightness level of the display be limited.

When a display device is in a standby, sleep or powered-down mode to save battery power, the display is at a zero brightness level. When the display is automatically activated, such as when a telephone call is received, the display could turn on to a brightness level determined by the ambient light level detected by the ambient light sensor.

If the device is in a car being driven at night, for example, then when a call or other triggering activity is detected, the display brightness level may instantly jump from zero to some predetermined level. Because the user's eyes are likely to be already adjusted to the darkness of the car, the sudden change in display brightness level from could cause luminescence shock and temporary vision impairment, which can be dangerous to the operator of the car, especially if the driver takes a glance at the newly illuminated display.

To avoid luminescence shock, if the display device is off and a call or other triggering activity is detected, the ambient light sensor will turn on and detect a certain ambient light level. In one embodiment, if the detected ambient light level is greater than or equal to a threshold value, then the display device will turn on at a brightness level according to the current display brightness setting. In other words, if the ambient light level is greater than or equal to threshold value, the display will turn on from a zero brightness level to the level defined by the appropriate brightness function as determined by the current display brightness setting. Because the threshold value is chosen such that no luminescence shock is expected for ambient light levels above the threshold value, no adjustment is made to the display brightness level when the display turns on.

However, if the detected ambient light level is below the threshold value, luminescence shock may occur, so the display device will turn on from a zero brightness level to an initially reduced brightness level as compared to what would normally be expected if the brightness function appropriate for the current display brightness level was followed. In other words, the display will initially turn on to a brightness level less than the appropriate brightness function as determined by the current display brightness setting; This dimmer than usual brightness level is intended to avoid luminescence shock. After some short time period has passed, giving the user's eyes time to adjust, the brightness level could be gradually or instantly increased to the level determined by the appropriate brightness function, which should be closer to ideal for sufficient visibility at the current ambient light level.

Apple's Patent FIG. 1 illustrates an exemplary computing system including a display device operable in accordance with a luminescence shock avoidance algorithm; Patent FIG. 2a illustrates exemplary brightness functions of ambient light (in lux (one lumen per square meter)) vs. display device brightness or luminance (in nits (one candela per square meter)) for an exemplary display device according to one embodiment of this invention.

Apple's patent FIG. 4 is a more detailed view of the host processor, ambient light sensor and display device shown in FIG. 1; Patent FIG. 3 is a plot of wavelength vs. pupil sensitivity, showing that the pupils are more sensitive to blue/green light as compared to red light to illustrate the purpose of gamma-shifting according to one embodiment of this invention.

Apple credits Kai Achim Pantfoerder as the sole inventor of this patent which was originally filed in Q2 2007, prior to the iPhone's official launch.

Notice: Patently Apple presents only a brief summary of granted patents with associated graphics for journalistic news purposes as each Granted Patent is revealed by the U.S. Patent & Trademark Office. Readers are cautioned that the full text of any Granted Patent should be read in its entirety for full details. About Comments: Patently Apple reserves the right to post, dismiss or edit comments.