Always-on on a Garmin AMOLED: what the 10 % rule actually means
Lower your wrist and the face on an AMOLED Garmin goes almost empty: the time stays, the rest disappears, and often the display shifts by a few pixels. That is not the developer cutting corners but a rule of the platform. A face that ignores it does not get dimmer, it gets switched off.
The three rules
In always-on mode a Connect IQ watch face may update only once a minute, and it may light only a fraction of the display. Garmin's own developer documentation put that fraction at ten per cent of the pixels, and added a second limit for the Venu and Venu Sq series: no single pixel may stay lit for more than three minutes. The three-minute rule is why so many always-on layouts drift slowly across the screen instead of sitting still.
With API level 5.0.0 the first rule changed shape. The check is no longer counted in pixels but in luminance: the screen stays on if the face uses less than ten per cent of the total luminance of the display. The budget stays the same, only the counting changes, and that is a gain: you can light more pixels as long as they are dim, or keep a few bright ones. A hundred per cent of the display at ten per cent brightness and ten per cent of the display at full brightness both sit at the limit.
The part that surprises people is the enforcement. There is no warning dialogue and no review that catches it. If a face breaks the rule while it runs, the watch turns always-on off for that face. Your display goes dark on wrist-down, and the face looks broken rather than over-budget.
What that does to a design
Three things follow from the budget.
The background goes black. Not dark grey, black: on AMOLED an unlit pixel costs nothing, and every pixel you tint eats into the same budget that the numerals need. A gradient that looks rich in the active view is unaffordable when the wrist drops.
Colour goes away. An accent colour is not free; it is lit pixels. In an always-on view it competes with legibility for the same ten per cent, and legibility should win. This is why good always-on views look monochrome, and why a face that keeps its brand colour when dimmed is usually spending budget on decoration.
Size beats weight. A thin, large numeral lights fewer pixels than a small, bold one and reads better at arm's length. The instinct to make dimmed text bold is exactly backwards.
And then there is position. On the devices that carry the three-minute rule, something has to move. Shifting the whole block by a few pixels every couple of minutes satisfies the rule and also spreads wear across the panel, which matters more than the rule does.
How to check a face yourself
You do not need the source to test this. Install the face, set the display to always-on in the watch settings, and leave the watch alone with the wrist down for a few minutes. If the screen goes dark by itself while always-on is switched on, and sleep mode and battery saver are ruled out, the face is over budget on your device. If the numerals stay readable at arm's length without turning your wrist, the developer spent the budget on the time rather than on ornament.
Developers have a sharper test: in the simulator, disable burn-in protection, pick an AMOLED device on the current API level, and switch the display mode to always-on. A face that exceeds the limit is reported instead of silently degrading.
Why the rule exists
Burn-in is not theoretical. There are documented cases of Garmin AMOLED panels showing permanent ghosting after years of always-on use, with static labels still faintly visible when the screen should be showing something else. The ten per cent budget and the three-minute rule are the cheap insurance against that, and they are the reason a well-built always-on view looks almost empty.
How Umbra handles it
In Umbra the always-on view keeps the time and date large, drops everything else, turns the background black and shifts its position every minute; the full layout returns on wrist raise. We measured this in the simulator per resolution class, not over weeks on the wrist, which is why there is no percentage here.