Measured actual electrical on my tank

[Delphinus]

I guess the real question is what are the real watts out of a 400W? It's like the 250W M80 is more like a "real" 400W. Looking at Sanjay's site ( http://www.manhattanreefs.com/lighting ) I note that switching to an electronic ballast for 250W the XM lamps drops to 115.

Assuming an electronic ballast really uses 250W (might be a stretch, I don't know), and we get 115 ppfd, that's like saying 0.46 ppfd per watt. If the HQI uses 405W but nets 182 ppfd, that's also 0.45 ppfd per watt, but we just "get more". So I guess it's not a real question of who's more efficient, but a question of how much PPFD do you want.

Wow, my head is swimming just trying to digest this. I knew that a 175W wasn't really 175 and 250W wasn't really 250 and 400W not 400W but I thought the "real versus rated" differences would be less than this.

Dang maybe T5's really are the way to go in the future.