There was a simple way to get ambilight data …
This is not a supported technique. The general rule for I/O Kit is that infrastructure prefixed with IO is intended to be API while infrastructure with other prefixes, and that specifically includes Apple, is not. Calling undocumented methods on undocumented I/O Kit user clients is not the path to long-term binary compatibility, and it seems that the Touch Bar Macs are helping to illustrate that fact.
As far as I know there is no supported API to get ambient light values on macOS.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
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