The first thing to keep in mind when asking this question is that the v4 blades' primary purpose is dueling. They are thick walled, and high quality blades that won't break or shatter when being used. That being said, there are other blades on the market that may illuminate a touch more fully (Vader's Vault has some good options... for display-only blades) than a v4. But.... Personally, I find the illumination on the v4 to be perfectly satisfactory; I've never had a complaint about dull spots or anything of the sort through the blade, and find their tip illumination among the best of the blade types I've personally owned.
As you can see from this picture, the light does tend to flare out at the base of the saber, but I don't think it really tapers off, either. Personally I really like this, it tends to add what I feel is a realistic flare to a blade.