Hi Daniel, Ambient light sensor is trying to match the brightness sensitivity of human visual system. Please see the following links: http://en.wikipedia.org/wiki/Color_vision#mediaviewer/File:Eyesensitivity.svg http://en.wikipedia.org/wiki/Color_vision
You can compare the spectrum with the datasheet. The green channel is matched with ALS spectrum. Kevin Tsai 03/02/15 -----Original Message----- From: daniel.bal...@gmail.com [mailto:daniel.bal...@gmail.com] On Behalf Of Daniel Baluta Sent: Monday, March 02, 2015 1:57 AM To: Daniel Baluta Cc: Jonathan Cameron; Kevin Tsai; Hartmut Knaack; Lars-Peter Clausen; Peter Meerwald; linux-...@vger.kernel.org; Linux Kernel Mailing List Subject: Re: [PATCH] iio: light: Add support for Capella CM3323 color/light sensor On Sun, Jan 25, 2015 at 12:50 PM, Daniel Baluta <daniel.bal...@intel.com> wrote: > On Sun, Jan 25, 2015 at 12:27 PM, Jonathan Cameron <ji...@kernel.org> wrote: >> On 22/01/15 10:10, Daniel Baluta wrote: >>> Minimal implementation providing raw light intensity and illuminance >>> readings. For illuminance user can compute lux values using raw >>> readings and scale. >>> >>> This driver also supports CM3323E sensor chip. >>> >>> Cc: Kevin Tsai <kt...@capellamicro.com> >>> Signed-off-by: Daniel Baluta <daniel.bal...@intel.com> >> >> Hi Daniel, >> >> My only real question on this one is whether using the 'green' >> channel and pretending it is a measure of illuminance is a good idea >> or whether we are better leaving that decision to userspace... >> >> I'm guessing the reason it is green rather than clear is that the >> clear is letting infrared through and we don't have an additional >> infrared sensor available to allow that component to be removed? > > Hi Jonathan, > > <snip> >>> +#define CM3323_COLOR_CHANNEL(_color, _addr) {\ >>> + .type = IIO_INTENSITY, \ >>> + .modified = 1, \ >>> + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \ >>> + .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_INT_TIME), \ >>> + .channel2 = IIO_MOD_LIGHT_##_color, \ >>> + .address = _addr, \ >>> +} >>> + >>> +/* >>> + * CM3323's GREEN channel is used for reading illuminance >> That's impressively random and unlikely to be anywhere near correct >> pretty much all the time! >> >> I'd personally prefer just not providing an illuminance channel and >> leaving it up to userspace to make the decision on whether the green >> channel is good enough... > > Datasheet says that the GREEN channel should be used for getting > illuminance readings. I'm not sure if this is totally random. > > I understand your worries, perhaps Kevin could 'enlighten' us here. > > I would prefer to have the illuminance channel exported from IIO > because there are already userspace applications/frameworks written > and tested for ALS that use IIO illuminance channel. > We want to use this driver without modifying user space. > > Of course, one option for the moment would be to only export the > INTENSITY channels as per your recommendation and to decide later what > to do for the LIGHT channel. Hi Kevin, Could you tell us how reliable is using the GREEN channel for getting illuminance readings? If no objection, I will resend this driver exposing only INTENSITY channels for the moment. thanks, Daniel. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
