There is actually a variant of this for horses. here http://www.albedo100.co.uk/product/horse_and_pets/hp_reflective_spray.html
The same company makes one for fabrics too. We spray the horse's quarters (with the horse one) and the back of the jacket (with the clothing one) for when my daughter is hunting. On occasion the field is very late back and on the roads at dusk. And of course none wear hi viz. It is just a bit more protection. It does wash out though so no good in persistent or heavy rain. Obviously proper hi viz is better and I don't want to spark a debate on whether hunts should wear hiviz or not - it is just another "tool in the box" so to speak.
You can spray designs on the horse which reflect under show lights.. but we've not done that.
He he I can see me having a glow in the dark horse lol!
On a more serious note do these cyclists not think to wear proper hi viz and reflective at present? I didn't see many wearing anything other than dark clothes so no wonder they dice with death every day!