Users may reduce the backlight brightness to 0% using the brightness-down (F6) key this may be desirable to conserve battery power while streaming music. The screen is turned back on in response to user activity (which is interpreted broadly: keyboard or touchpad activity, power source change, external display being connected or disconnected, etc.). When the user is inactive for an extended period of time, the screen is dimmed to 10% of its maximum level (computed linearly) and then turned off. We decided that always booting with a reasonable default brightness was preferable to sometimes restoring a blindingly-high brightness when booting in a dark room or restoring an extremely-dim brightness when booting in a bright room. A given device is frequently used in many different environments: dark rooms, well-lit rooms with lots of ambient light, etc. In the past, the previous user-configured level was restored at boot, but this was deliberately removed. The brightness popup that appears when a button is pressed actually contains a draggable slider that can be used to select a brightness percentage that doesn't match one of the pre-defined steps. each button press moves the brightness by 100 / 16 = 6.25%).
#Brightness control on chromebook full#
(Prior to M36, separate user-configured levels were maintained for AC and battery power - see issue 360042.) There are 16 user-selectable brightness steps, divided evenly between the full non-linear percentage-based range (i.e. issue 826968Ī single user-configured brightness is tracked for both AC and battery power once the user has adjusted the brightness via the brightness keys, the brightness remains at that level until the next time the system boots. With the better ambient light sensor in Pixelbook, auto-brightness levels are more finely-tuned and consist of 7 levels as follows: SituationĪlso, as of M66 Pixelbook performs simple exponential smoothing to raw values read from the ambient light sensor as a low-pass filter to remove noise from the data to avoid adjusting the brightness too frequently in some lighting conditions such as an overhead source of warm white LED lighting. When the user presses the brightness-up or brightness-down keys, powerd animates to the requested level and stops making further ambient-light-triggered or power-source-triggered automated adjustments until the system is rebooted.
#Brightness control on chromebook update#
Before the user has touched a brightness key, the brightness will update automatically between when AC power is connected or disconnected. When the power source or ambient light level changes, powerd transitions to the new brightness level. We decided to switch to just two levels: one that would work well in most indoor environments, and a very-bright level for outdoor environments. Due to the coarse readings within this range, the automatically-chosen brightness levels were frequently undesirable. This was distracting to users and also generally ineffective: the majority of indoor environments occupy the bottom end of the range reported by our ambient light sensors. In the past, powerd made continuous adjustments to the screen brightness based on the ambient light level. Note that these levels may be set differently for different devices. The automatically-chosen levels are as follows: Power sourceĭevices that lack ambient light sensors just use the “normal ambient light” levels listed above. Level = min_visible_level + fraction² * (max_level - min_visible_level)
Given a hardware-specific minimum-visible level and maximum level, the mapping from a percentage to a hardware level is defined as: fraction = (percent - 6.25) / (100 - 6.25) Note that the brightness percentages appearing in powerd's log are not computed linearly (see policy::InternalBacklightController::PercentToLevel() for the implementation). direct sunlight, or something dimmer than that). This happens before the boot splash animation is displayed by frecon.Īfter powerd starts, it chooses an initial backlight brightness based on the power source (either AC or battery) and the ambient light level (either very bright, i.e.
Please update any links:Īt boot, the panel backlight's brightness is set to 40% (computed linearly) of its maximum level by the boot-splash Upstart job. Warning: This document is old & has moved.
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