Here is one of personnel experience, Around 2003 I set up a 158 and after a year I changed lighting from CFL’s to MH DE 250w’s. Added SPS and everything was doing great, except a little hair algae. Then after about eight months my SPS started to RTN and die. I checked water quality and everything seemed normal. So I checked my lighting with my meter, something I had not done since I had set it up because typically MH lamps last a year? To my surprise my lamps had lost 50% in 8 months! And trust me you can not tell with your eyes, because to me everything looked the same both color and brightness.
I am guessing the lamps I received where from a bad batch because I have never heard of anyone else having the issue of bad lamps in eight months, but if it can happen once it can happen again.