Spread the beam.. diffuse it.. expand it.. lots of ways. Lasers are usually adjustable via collimating lens.. or a series of Lab lenses.. I would just use one or a few, with a nice mirror finished shroud to get as even distribution as possible all while being able to automatically adjust light...
This.
Different results from different wavelengths. You also have nearly full spectrum lasers these days so it wouldn't be too much testing. The UV lasers will obviously help destroy some bacterium or other organic parasites and disease.
They use red for certain plants and blue for certain...