Dr. Sanjay Yoshi used to have a site that you could compare all this in. I can no longer find it on the web. I played with de vs. mogul in the 250w range for a long time. Ballast that drove the de bulbs was the biggest pitfall i came across. Both de and mogul bulbs in an appropriate wattage will light any area with enough par, color on the other hand is where most cannot make a decision on which to choose. Icecap electronic ballasts and comparable ballasts do not give de bulbs the color that a true hqi ballast does in my opinion. I had icecaps and instead of buying new ballasts and bulbs i changed back to mogul, but in 400 watt. I am very happy with that choice and will stay with moguls, although phoenix 14k de bulbs on a true hqi ballast are beautiful. So lighting in regards to par will probably not be a problem, at least in 250w. In 150w i cannot say it is enough as i have never gone that small in wattage. A borrowed par meter can answer that question, and if it is enough par for you and you like the color it gives your tank then your quest is over. Good luck!