Water meter reader

I wanted to read the data of my analogue water meter with an arduino. The water meter has a small cog wheel made of some reflecting material. Just have a look at the images. The first idea was to illuminate this wheel with a bright light source and detect the reflected light. After a lot of experimenting I had to drop this idea. The problem was, that the cog wheel did not reflect the light uniformly for each tooth. Some teeth did reflect the light to the sensor while some other teeth did not.
So the next idea was to measure the reflected light intensity of one of the red arrows. The arrow with the 0.001 scale measures 1 litre each turn. A green super bright LED was used to illuminate the water meter display and a photo transistor with a simple amplifier should detect the signal.
It is important to use a green LED because green is the complementary color to red. The red arrow will absorb most of the green light while the white background will reflect most of it.
The first try withou