LED uniform light spread
I think you are talking about "frosted glass" or a diffuser. You can reflect the LED light off of a white, matte surface in order achieve diffusion. You can use holographic diffusers (efficient, generally) or ground glass or use hydrofluoric acid to "frost" the glass surface. I've even used waxed paper in a pinch (needed a quick diffuser for a fiber optic connection.)

It's impossible to say what the appropriate technique in your case is, though. Not without a lot more information from you. And even then?

But there are some of the techniques.

(You want the opposite of specular reflection, instead looking for a perfect Lambertian distribution of reflected light where the surface brightness looks about the same from any angle.)



I don't understand how 'uniformly' you have to get, but to take one LED output and to spread it out uniformly over an area will require some kind of a diffuser. One of the problems with diffusers is that they tend to disperse the light everywhere (by definition) and the intensity in some specific target area will integrate to a smaller value than before. But that is something that comes with the territory. (Holographic diffusers help here.)

Some LEDs come with a milky epoxy to help out. And you could consider modifying the LED itself, by sanding it or otherwise attempting to make it disperse the light differently.

What have you tried already and why is a diffuser out of the question?