As I expected, it needs additional optics to be useful. Consider a sheet of fluorescent film you put on your eyeball. If there's an omnidirectional point source

As I expected, it needs additional optics to be useful. Consider a sheet of fluorescent film you put on your eyeball. If there's an omnidirectional point source of light, it would excite the whole film virtually uniformly. Hence the upconversion contact lens needs to lie on some sort of a focal plane to be useful.