The older Aristo cold lite heads had a V4500 tube in them and needed a CC40 yellow filter to enhance the light out for use with the full VC filter set on variable contrast paper! I don't know what tube is in that cold lite head!But most variable contrast papers have two emulsions in them, one sees only blue and is high contrast and relatively fast and the other sees only green and is low contrast and is relatively slow! The older cold light tubes were high blue output, that's why they needed a CC40 yellow filter.