A brightness acuity game. See copious comments in-line. Runs on the BBC micro:bit.

acuity.py

# Light acuity game. A pixel will change on either the
# left or the right. Click the appropriate button within
# an ever decreasing amount of time to increase your score.
# The game is over when you get it wrong or don't answer
# in time.
# Based on an idea by Dave Gibbs.
# By Nicholas Tollervey, Feb. 2016. Released to the public domain.
from microbit import *
import random


def change_pixel():
    # Randomly selects a pixel on the left or the right and changes
    # its intensity. Returns the x coordinate.
    x = random.choice([0,1,3,4]) # Don't select the middle column
    y = random.randint(0, 4) # Y row can be any row within range 0, 4
    # These lines ensure there's always a change of intensity from
    # the current value.
    current_intensity = display.get_pixel(x, y)
    valid_intensity = list(range(0, 10))
    valid_intensity.remove(current_intensity)
    # Remove the intensity values either side of the current one so
    # that there's enough of a difference in contrast.
    if current_intensity < 9:
        valid_intensity.remove(current_intensity + 1)
    if current_intensity > 0:
        valid_intensity.remove(current_intensity - 1)
    # Select a new intensity and update the display.
    new_intensity = random.choice(valid_intensity)
    display.set_pixel(x, y, new_intensity)
    # Return x so the game can judge which button to detect.
    return x
    

def play():
    start_image = Image("99999:" * 5) # all pixels at full intensity
    wait = 2000 # you have 2 seconds to get it right (at the start)
    score = 0
    # play the game!
    display.show(start_image)
    sleep(wait)
    # Game loop
    while True:
        wait -= 100 # Speed up the wait time.
        x = change_pixel() # Make a change.
        sleep(wait) # Wait a while...
        if x < 2 and button_a.was_pressed():
            # Button A was pressed and change was on left.
            score += 1 # Correct!
        elif x > 2 and button_b.was_pressed():
            # Button B was pressed and change was on right.
            score += 1 # Correct!
        else:
            # All other cases = end of game.
            break
    display.scroll("Score = {}".format(score))

play()