    **********************
    ambLight_pi.py    *
    **********************
    reads a photoCell
    **********************
    A photo-cell can be used to measaure the analog value of ambient light, but it can
    also be used as a binary (digital) value of light/dark.  Total darkness occurs when
    the photo-cell is covered (e.g. by a finger).  This light/dark situation is similar to a push-button
    which is what digLight returns as a binary value.  Because the Raspberry Pi cannot read
    analog values,  an external ADC device is necessary (e.g. WeatherHap Pro, Pico, Seeed PN
    03030279  that uses a ti ADS1115.)   The related digital routine digLight can be used
    to measure light/dark as a binary value without need for an ADC.
    Also for Seeed ADS1115 Raspberry Pi board (AIN0,AIN1,AIN2,AIN3).
    /Note.html