Lighting question

[PeeperKeeper]

I have a 75g, currently a FOWLR, lit with one pair of 96W PC's. I want to upgrade the lights and go with more reef. I want to have the option of SPS, but it won't really be an SPS tank most likely.

I thought I had decided on 4 - 6 54W T5's (as seen here: http://www.reefgeek.com/products/categories/lighting/104069.html or here http://coralreefbazaar.com/product_info.php?products_id=68 ) but it was recently suggested that I look at a set of VHO (as seen here: http://www.hellolights.com/4654lamvhore.html ).

Before anyone suggests MH, I like the shimmer effect of MH, like everyone else, but I'm concerned about heat and my hood not being tall enough, and I already have a ton of evaporation with just the single fan on my tank (and my chiller is sold, lol) so I don't want to do MH.

I've heard T5's have low heat production, but is it lower than with VHO, or with my current PC's? I think the answer is yes compared to PC's because my PC's get pretty hot, and when I was looking at some T5's on a tank in a LFS, you could hold your hand on them when they'd been on for hours. So what about heat with VHO's?

And what's all this I hear about PAR? Does that refer to having more of the "type" of light corals need, and does that have to do with the wavelength or water penetration (I know WL and pen. are related) or intensity or something else?

Oh, if anyone wants to suggest a specific good deal on lighting, I'm finding one of my major limiting factors is that the inside of my hood is exactly 47 1/8" wide and most of the 48" retrofit kits are slightly longer than that. I am most definitely open to any offers of used lights which fulfill my needs!

[hobogato]

send a pm to don-in-sa, or seamonkey2, they both have really nice tanks on T5 lighting and would be able to give you some good advice.

[GaryP]

PAR is "photosynthetically available radiation." In other words the amount of light a bulb produces that a plant is able to use for photosynthesis. Basically, the lower the K value, the highter the PAR. A 6.5K bulb has about 1.5-2 times as much PAR as a 10K and 3-4 times as much as a 20K bulb. The bad news is the lower the K value the less "pretty" the colors look to the human eye. So that means you have to use more bulbs and more electricity to get the same PAR if you are using a high K value bulbs. Most fluorescent bulbs are usually used as a combo with daylight and actinic bulbs to get some sort of combination. These are often sold as 50/50 type bulbs. Most folks that are using MH will combine them with an actinic fluorescent to achieve the same thing.

On top of all this, if that wasn't complicated enough, you have the issue of actinic vs. "true actinic." lights. Some bulbs that are sold as actinic are actually blue and peak at around 460 nm. True actinic is purple and at 420 nm. 420 nm is thought to result in increased pigment production in some corals. Since its close to UV, they produce these colored pigments as a protection from the UV, just like we produce melanin and tan as a result of exposure to UV. 420 nm basically fools the corals into thinking they are getting sunburned without exposing them and the fish to the negative effects of UV. That's the theory anyway. :)

[PeeperKeeper]

Thanks for the explanation of PAR, Gary. Let me make sure I understand the difference between what lower K lights do and what actinic does. The K stands for Kelvin, and that is a temperature scale, right? And the "color temperature" refers to when you heat up a metal and it glows with heat, it starts out in the red range and goes up through white and blue (or does it just get whiter, not blue?). Anyway, so when you say 10K, you actually mean 10,000 K, because that is a higher color temp and therefore whiter than 6500K, right?

You said photosynthesis happens better in lower/redder color ranges, but you also said corals produce better pigment in bluer color ranges. Okay, as I typed it I realized we're talking about two different things, photosynthesis in the symbiotes vs pigment of the coral, not production of symbiotic organisms to produce the color. Got it.

Now I understand the PAR you get and "prettiness" of the light depends more on the color bulbs you choose and the wattage than whether it's VHO or T5. I'm still wondering about VHO's vs T5's as far as amount of light and heat produced per bulb.

[GaryP]

I think temp is more dependent on total watts then the type of bulbs. As I understand it, the chief advantage to T5 is the effectiveness of the reflectors you are able to use on them because of the small size of the bulb. This allows you to get more light for less watts, thus less heat. VHO have an internal reflector in the bulb itself that is not highly effective. OK, that said, I have never seen a tank using any type of fluorescent bulbs that had a serious heat management problem. I have 440 watts of VHO on my 75 gal. and use one small cooling fan with no major problems. It isn't until you get up to MH, and especially 400 watt MH that you really need to jump through hoops for heat management. The chief disadvantage to T5's is that I am only aware of 1 brand of T5 that makes a true actinic bulb, and as I understand it they are pretty pricey. I'm sure one of the T5 users will jump in here with info on that. T5's are still a relatively new technology and has still not shaken out. They have only been on the market for a couple of years and only had a major impact for a little over a year. I've been using VHO for over 10 years and tend to stick with what I am comfortable with.

Another note. The other big factor impacting PAR is the age of the bulb. All fluorescents have to be replaced regularly. 6 months is probably the average useage time. MH are good for a year, although their output starts to begin decreasing in output within a month after they are installed. Its simply a mature of balancing cost vs. performance. A car doesn't perform as well as it does when its brand new, but we don't replace them every year either.
T5s made a big splash when they were first introduced because the manufacturers claimed they could be used for 2 years. How a bulb that is basically the same technology as other fluorescents was capable of that was beyond me. I don't hear anyone making those sort of claims anymore. I have heard that a lot of the "early acceptors" that made a change to T5 for SPS tanks are making the move back to VHO now. In those tanks, MH will always be dominant and fluorescents are only used as supplemental actinic bulbs.

The tank I am working on now is going to 6 X 160 watts of VHO actinic.

[alton]

I had a temporary set up of 2 - 54w T5HO Actinic and 2 - 10 K 54w T5HO. Each lamp had it's own reflector and it compared to the brightness of 4 - 65w Compact Fluorescents. If your wanting to go with T5 HO's I would go with 6. The brighter the light the more heat it will produce.