Re: [RFC 0/4] iio: light: add driver for Broadcom APDS9999

["Jose A. Perez de Azpillaga" <azpijr@gmail.com>]

On Mon, May 11, 2026 at 04:53:10PM +0100, Jonathan Cameron wrote:
> On Mon, 11 May 2026 17:19:54 +0200
> "Jose A. Perez de Azpillaga" <azpijr@gmail.com> wrote:
>
> > On Mon, May 11, 2026 at 01:21:12PM +0100, Jonathan Cameron wrote:
> > > On Mon, 11 May 2026 12:14:42 +0200
> > > "Jose A. Perez de Azpillaga" <azpijr@gmail.com> wrote:
> > >
> > > > This series adds support for the Broadcom APDS9999 ambient light
> > > > sensor. The APDS9999 is a digital proximity and RGB sensor with
> > > > ALS capability, featuring I2C interface, programmable gain and
> > > > integration time.
> > > >
> > > > This chip is considered by Broadcom to be the 'successor' to the
> > > > APDS-9960 which has technically been discontinued.
> > > >
> > > > The initial driver implements the ALS/Lux functionality using the
> > > > green channel, which approximates the human eye spectral response.
> > >
> > > That's not normally a good approximation unless it is also has
> > > very bad colour curves for green!  Better than any other channel
> > > on it's own but still not good. If we had calibrated sRGB it would be:
> > >
> > >  Something like: 0.2126R+0.7152G+0.0722B
> > > for example.
> > >
> > > The lux vs white light and lux vs incandecent light are fairly linear
> > > so 'maybe' it's good enough but it's a bit of a stretch to describe it
> > > as an illuminance measure which is what we'd need for it to be measured
> > > in lux.
> >
> > the datasheet states: "Approximates human eye response with green
> > channel" and "Uses optical coating technology to emulate human eye
> > spectral response."
> Hehe. Marketing. They provide the light curves that show it approximates
> very well the green part of human eye spectral response and very badly the
> rest of it! :)

haha. fair enough.

v2 will keep thr IIO_LIGHT channel and add IIO_INTENSITY for all four
channels so userspace can do its own weighted lux.

--
jose a. p-a