A single glass filter is mounted in the optical path of the camera, outside the waterproof view window. The filter keeps the camera from seeing UV light. This highlights weak visible fluorescence when it is present. The filter can be removed and changed to filter out the UV at different wavelengths. The overall effect of the filter is to greatly increase the contrast between the fluorescence and the background.
Live roots are light blue against a black background.
Bends in the roots fluoresce more than the straight sections. Some brown roots fluoresce more than white roots, which reverses the natural bias we might have to count the high contrast white roots we see under white light. Also, some roots show up that don't appear at all under white lighting. Further study of the fluorescence might correlate age or chemical status to the differences in fluorescence now clearly shown between roots on the screen. The blue fluorescing image against a black background may be digitized and measured with a computerized image processor.