Did you look at this thread, a few posts behind ?
I want to expand on KMT’s answer here:
There is no Public API that allows that access.
He’s absolutely right. There is no supported way to read the ambient light sensor on any of Apple’s platforms. You may see various posts about techniques for doing this, but:
These techniques are unsupported. They all depend on private APIs, or infrastructure that’s considered private.
Using private APIs is likely to cause problems with App Review.
Even if you product doesn’t go through App Review, you may run into compatibility problems down the line. This may be the result of the sandbox getting better at restricting access to private APIs, or it may just be accidental breakage caused by architectural changes. For an example of the latter, read this thread.
DevForums is not the right place to discuss unsupported techniques.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"