Theory of clean vs dirty lights depends on the electronic ballast technology used. Grow lights used with baddass ballast, provide clean light & maximum output.
Are you planning to set up your own hydroponic system? Then there are certain crucial factors, which you need to take care of like temperature, humidity, and pH level. pH is probably the most overlooked aspects when it comes to hydroponic systems. However, it is a very important factor ad can deter growth of plants if not set right.