Welp, after much deliberation and help from members around here, I pulled the trigger on the Marineland Aquatic Plant LED 24-36" with timer
. (I got mine for $211.99 from amazon in March 2013).
First, the actual unit measures 22 3/4" - but you'd have to allow for 24" of width for the power cord coming out of the side. You can use the wire brackets on either end (that extend to 36" wide) to sit on the side of the tank, or they work just as well as stands to sit on a glass canopy. The wire stands also pull completely out if you like. The width left a few inches on either side on my 30" wide 29gal - but I think the light coverage to the sides of the tank is pretty good.
The unit does get pretty warm... I can't hold it for too long before I have to sit it down when I'm taking it off my tank for something. The whole unit is built like a heat sink.
I love, love, love the timer! It comes set from the factory;
9am: blue lights
10am: all lights (white & RGB)
8pm: blue only
10pm: all off
All you have to do is set the time of day. And it's surprisingly simple to change any of the timing settings, even though there's only 2 buttons. If you turn on the blue or white lights and override the timer, you won't effect the timer's cycle - it'll keep on trucking.
The Red/Green/Blue LEDs (middle row, every other light) have diffuser lenses on them, and that is pretty effective at spreading the light from those LEDs around the tank. The RGB lights make a real difference in bringing out the colors in the fish and plants - things look more interesting! The rest of the regular white LEDs are relatively focused, which gives that awesome shimmer effect that's impossible to capture in a picture.
I was wondering how the brightness and color was going to compare to what I had. For those with the same question, I put my old light back on the tank and took shots with the same camera settings. It makes the "before" shot too dark for a proper photo, but makes for a good comparison:
With Ecolux Plant & Aquarium F20T12-PL/AQ-ECO Wide Spectrum 20w fluorescent bulb:
With Marineland Aquatic Plant LED 24-36":
And finally the moonlight. I dig it. I'm surprised by reviews that say the moonlight on this fixture is much brighter than the moonlight on even the double-brights. I wouldn't want it any dimmer at all - wouldn't be able to see anything!
Though since the "blue" light is also on with the white lights (as part of the RGB LEDs) I wonder if they will go first. But it's nice that this light is rated at 50,000 hours (unlike the Marineland single and double-brights that are only 17,000 hours). That's the same rating as Marineland gives their 10,000k Reef-capable lighting, but this one is at the more appropriate 6500k for freshwater
I know I sound like a little Marineland fanboy, because that's all I've talked about here... I did consider Finnex for a time but the fewer LEDs on this Marineland (instead of more, smaller LEDs on the Finnex) gives a better shimmer effect, which I like a lot. That + the built-in timer = I'm very happy.