I made an image to explain it. The grey area (conceptual, I don't know how big it is), shows wave lengths blocked by the glasses. As you can see those wavelengt

I made an image to explain it. The grey area (conceptual, I don't know how big it is), shows wave lengths blocked by the glasses. As you can see those wavelengths give strong activation of both red and green cones. The remaining wave lengths activate just one or the other. This mean if a light source has both green wavelengths and yellow wavelengths, the filter will remove the yellow ones, making it look green instead of yellow. One form of color blindness arises when the green and red peaks are especially close, making a large span of wavelengths look yellowy. By filtering those out, the person can get color vision. http://i.imgur.com/dMlzKUN.png http://i.imgur.com/dMlzKUN.png