An ambient light sensor is a little chip that you’ve certainly got in your tablet, most probably in your phone and you might even have one in your laptop if you’re lucky. Ambient light sensors let us change the panel brightness so that you can still see your screen when it’s sunny outside, but we can dim it when the ambient room light level is lower to save power.

Not many laptops have ambient light sensors; of the ones that do the driver support is really bad and they often return garbage values. As hardware support is so bad, we’ve not got any software that actually uses the ALS hardware effectively.

I've spent a bit of time over the last few months designing a small OpenHardware USB device that acts as a ambient light sensor. It’s basically an uncalibrated ColorHug1 design with a less powerful processor, but speaking a subset of same protocol so all the firmware update and test tools just work out of the box. The device sleeps between readings, so only consumes a tiny amount of power. With hardware that we know works out of the box, we can work on the software integration.

The sensor itself is a very small (12x22mm) printed circuit board that inserts directly into a spare USB socket. It only sticks out about 9mm from the edge of the laptop as most of the PCB actually gets pushed into the USB slot.

ColorHugALS can currently control the backlight when running the colorhug-backlight utility. The Up/Down header buttons do the same as the hardware BrightnessUp and BrightnessDown keys. You can still set the absolute backlight so you're in control of the absolute level right now, the ALS modifying the level either side of what you just set in the coming minutes. The brightness is modified using a exponential moving average, which makes the brightness changes smooth and unnoticeable on hardware with enough brightness levels.

We also use the brightness value at start to be what you consider "normal" so the algorithm tries to stay out of the way. When we've got some defaults that work well and has been tested the aim is to push this into gnome-control-center and gnome-settings-daemon for GNOME 3.18 so that no additional software is required. The ColorHugALS device CANNOT be used to calibrate your screen and so is only suitable for ambient light measurements.

Get your own ColorHugALS for £20

This includes free worldwide shipping. Please only order this product if:

  • You agree Hughski Ltd. can't be held responsible if your computer is damaged or stops working after using the ColorHugALS.
  • You will have to pay any applicable customs charges or import taxes when we send the ColorHugALS to any country which is outside of Europe. The label will state the value of the object is £20 and is described as color calibration hardware.
  • You understand there are no Microsoft Windows or Apple OS X native drivers included with this product and you need to have colord >= 1.2.9 and colorhug-client >= 0.2.6 installed. Only GNOME >= 3.14 is supported at the moment.

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