If the screen has a hotspot then you put too much wax on it. The reason why older screens are dim is because the grind of the screen is rough. The wax fills in some of the ridges thereby increasing the transparency. If you use too much, you fill in all of the edges that refract the light. If you have a hotspot, you need to thin the wax so use whatever solvent you need to do so. Keep in mind you can take off the marking on the screen with some solvents. Be careful.
The other alternative is to place a fresnel over the screen or of course just replace the screen with something modern. The wax trick works though if you do it right.