Endless thoughts....
1. with electronic ballast you will actually be using the rated wattage or very close to it. With magnetic / hqi ballasts the actual watts used vary a lot from the ratings, ie a lot of DE bulbs run on magnetic HQI ballasts use closer to 350W. Standard magnetic ballasts also vary a lot in actual watts used, but the HQI's pretty much universally push more juice into the bulbs. Point being not all 250w set ups are really 250watts.
2. DE lamps appear to be more efficient in design, in that the smaller bulbs allow more efficient reflectors - DE lamps generally give a very focused light distribution, SE lamps tend to spred the light out more which is not necessarily ideal for putting the light into the tank (though they do a good bit better with "diamond lumanarc" reflectors compared to other SE reflectors). Also, I think that because the DE bulbs are a lot smaller, the bulb itself doesn't block it's own reflected light from getting into the tank.
3. I have been told (there are many takes on this) that the electronic ballasts "underdrive" DE bulbs - some say that this shortens blub life, others say it prolongs bulb life??? Either way the lumen output IS less with electronic ballasts, and generally the color of the same bulb will be different on electronic vs magnetic ballasts.
4. DE lamps are clearly more popular these days. The consensus is that a 250W DE lamp is just about equal to a 400W SE lamp. (keep in mind that that's comparing a DE lamp using up to 350W to a SE lamp that may be using right around 400W ???
5. IME, looking at a 250 DE HQI compared to a 250W SE on a standard ballast, well there's no comparison, the HQI puts out a lot more.
6. Up until reccently you couldn't really get a good DE HQI retro/DIY set up. This used to mean a major cost difference in set up. Now there are nice (I think, haven't seen one in person) DIY DE/HQI parts readily available - hence far less initial cost difference.
I would suggest DE lamps, but also suggest really looking at the performance #'s on HQI magnetic vs electronic ballasts (Par, watts used exct.. for different bulbs AND ballasts). Electronics run cooler, and use less juice, but they also put out less light and May or Maynot negatively affect bulb life and color.
The options are truely mindnumbing IMO. I suggest taking about 5 asprin and spending a long time studying sanjays testing (Google "sanjay reef lighting", his link will be the first hit)
Hope this helps, surely others will elaborate and or add more.
jk
