Illuminance click carries an ambiance light sensor, similar to something you would find in your smartphone to automatically regulate the brightness of your screen.
Now if smartphone screens were designed for certain species of snakes to stare at, a simpler light sensor would do. But those are overly sensitive to infrared by the standards of a human eye.
So the makers of the TSL2561 light-to-digital converter that’s aboard Illuminance click came up with a workaround: Put two photodiodes inside the sensor. One sensitive to the full-spectrum of light, the other sensitive just to infrared. Then use a formula to derive the amount of visible light from those two — basically you get a sensor reading that approximates the way the human eye perceives light.
If you’re a super-human coder (like Neo from the Matrix) maybe it’s easier for you to perceive light in binary values. Illuminance click uses MikroBUS™ I2C lines to communicate with the target microcontroller so you’ll have a way to see those too.
The ideal application of Illuminance click is for auto-brightness regulators on OLED or LCD displays (which saves a lot of power on the backlight). Or just for any other sort of automatic ambient light regulation.