Almost nobody knows. Yet light is the strongest external signal for the body clock: it shapes when you fall asleep, how alert you are in the morning, and how steady your schedule stays. The app shows your daily light picture and suggests only what research actually supports.
These targets come from an international consensus of circadian researchers (Brown TM et al., PLOS Biology, 2022) and are expressed in the units of the CIE S 026 standard. Ordinary lux describes the effect of light on the body clock poorly — so we measure differently.
Measured by a sensor, estimated by the camera, read from an instrument, entered by you, or calculated — always visible. A camera estimate is shown as a range, never as an exact figure, because a phone is not a measuring instrument.
Every recommendation carries a study, a level of evidence, and its stated limitations. Where the evidence is thin, the app says so.
If we do not know what the light was doing, the interval is painted neither bright nor dark. A fragment of data is not enough to show a score — and the app tells you that.
It does not diagnose or detect disease. It does not treat insomnia, depression or seasonal disorders. It promises no rejuvenation and does not "boost your metabolism". It does not replace a doctor and is not a medical device. A phone screen is not a light therapy device: it delivers hundreds of times less light than a circadian shift requires, so "light therapy from the screen" is not here and never will be.