from SPIRIT RIVER. Spirit River now has the ability to process fly tying materials with both UVF and UVR, just like Mother Nature. UVF is the fluorescent wavelength in bright colors which allows fish to see flies at greater distance in most water conditions. UVR is the reflective UV light that cannot be readily seen with the human eye, but is very visible in the animal and insect world. Bees use it to find flowers, mayflies use it to choose mates, and fish naturally key on it as a safe food choice.