I think Steve pretty much summed it up. Just to add to it, my PAR reading on the T5 were with the old bulbs so yes, the reading would have been higher with newer bulbs. Couldn't do that as I just recently borrowed a PAR meter for this testing and had no way to test when my bulbs were new. And I wasn't about to spend $250+ on new bulbs at this point :) I would love to see others posting PAR numbers from their fixtures so we can do comparisons.

And for the record, I wasn't making any claims as to comparisons with 250w or 400W MH as I haven't done any PAR readings from those but a guess as to where my light output would end up. If anybody else has let's see the numbers as it would be interesting to compare.

But what I do know is that with the LEDs lower down, at about 7 to 8 inches above the water I was seeing just over 500 PAR in the upper part of the tank and 300 just above the sand bed of the tank about 18 inches down. That's pretty good from my understanding. I didn't test with the fixture even closer to the water but if I lowered it to where I had the T5s then I suspect Steve is correct and PAR would be 600 to 700 in the upper part of the tank. Maybe I'll try it tomorrow and see. The reason I raised the fixture for now is that I would burn all my corals switching them from say 300 PAR to 500+ PAR. They need to be acclimated and I plan to slowly lower the fixture every few days to acclimate them to the higher light.

Give this article a read:

http://www.advancedaquarist.com/2010/2/aafeature2

It shows comparisons in air, not water but it's a start. Also you have to note that the LED fixtures used in the article are not the best. One is a PFO Solaris which used older LEDs that do not have the same output as the newer generations of emitters and the other is the Eco-Lamps one that under drives their LEDS at just over 1 watt instead of 3 watts. Even so they compared well to a high end T5 (about equal performance) and a 250W MH (a little less but not by much; about 15 to 16% less output). I guarantee you my fixture will outperform both the Solaris and the Eco-Lamps as I used very good Cree emitters driven at a full 3W and 1000mA for the whites and about 900mA for the blues.

Even so Dr. Joshi states that most Acropora and light loving corals will thrive at PAR levels of 300 to 400 which this fixture can provide throughout my tank if I wish. That's good enough for me. In a 30" deep tank for example you could keep high light SPS in the top 2/3 of the tank. I don't have a deeper tank to test on but I suspect PAR would still be close to 200 by 30" down. That's pretty good performance in my book.

For comparison purposes Eugene at Oceanic Corals tested their 400W MH fixture (in their LED spotlight thread) and says that PAR was 500 at 12" below the water. I had 400 PAR at about that depth with the fixture say 7.5 inches above the water. I'll try to test with the fixture closer to the water at 12" depth and see what I come up with.

But I think my 400PAR as tested so far shows pretty well against the MH.

Oh, and just to Spam my own thread a bit testing by the LED leaders at nano-reef.com shows that the drop off in PAR vs. depth is less with LEDs vs. MH. That makes sense as with the optics virtually all the output of the LEDS is focussed down into the tank. T5s and MH, even with good reflectors, probably have less cohesive light with more scatter from the reflectors as they emit in all directions and then rely on the reflectors to focus the light down if that makes sense.

Steve,

You'll have to read Ron's post after yours. The PAR measured with the low quality T5 fixture was on more than 1 year old T5 lamps and therefore a very poor comparator - forget about the height of the fixture comparison. Additionally, I'm less concerned about the comparison to T5s than I am to MH (the only reason I commented on T5s was because the comparison was hugely favorable to the LEDs based on the manner in which it was performed). Various qualities of LEDs make them favorable to T5s IMO. With that said, comparisons are being made all over the place to MH by retailers, manufacturers, and hobbyists. When you were standing on your soap box about MH a few months ago you pounded your chest about getting over 1000 PAR at the surface and 500 on the bottom of the tank. Clearly, the numbers being reported here don't fall in line with what you've purported constitutes adequate PAR for your SPS tanks.

And as far as the theory behind intensity drop in LEDs goes - it's just that: a nice theoretical expectation based on presumed qualities. Until there is some long term data for PAR the theoretical musings can carry on but with a healthy dose of skepticism.

First I think you are being overly critical of my light fixture. I would not call it low quality but about a middle of the road one. Sunlight Supply makes good fixtures and these were not much different then the first generation Tek fixtures in terms of lighting output. Slightly better reflectors and active cooling would improve it somewhat but how much do you think that would be? 10%? 20%? Secondly, while the bulbs were old, the only references I could fine say that T5s lose about 10% output over 2 years. The problem for reef tanks is the shift in colour which can lead to undesirable algae etc. But let's say that the degradation was 20% for the sake of argument. So my 300 PAR with the T5s could mean 375 PAR with new bulbs. Still much less than 500 PAR with the LEDs higher above the tank then the T5s were. Argue all you want but however you set up my test, new bulbs or not etc. my LEDs handily outperform my T5s. That's all I am claiming. I would love to test different lighting setups for comparison but I don't have easy access at the moment. Maybe we can do that and arrange to test various people's lights with the same meter which will give some idea. it's not as good as a side by side comparison under the same conditions in the same tank but it would be a start.

I would also take manufacturers claims with a grain of salt as they are in the business of marketing their products and most likely set up tests to skew results in favour of their products. However, independent test are being done like Sanjay Joshi's comparison I linked in my last post. That clearly showed the "lower quality" LED fixtures performing as well at or slightly better then a high end T5 fixture and only 15 to 16% lower output then a good 250W MH setup. Dr. Joshi is an engineer and has been testing all sorts of lights, especially MH, for a long time so I would consider him a good independent reviewer. Here's also a more recent review of a top of the line LED fixture, the AquaIllumination:

http://www.advancedaquarist.com/2007...searchterm=PAR

This one clearly shoes the AI unit outperforming a 250W MH unit. Granted, the MH ballast used may not be top of the line but is probably typical of one used by many people.

With respect to who has the biggest PAR; really, who cares. Stoney corals appear to photosaturate between 400 and 500 PAR so having 700 or 1000 PAR is probably pointless other than for bragging rights. I doubt it will do the corals much good.

As for longevity and degradation of LEDS, that is fairly well established. While high powered LEDs are fairly new to our hobby they have been around for a decade and are well tested. Low power LEDs have been around far longer then that so the degradation of LEDs is well understood.

You have done a great job, look amazing! Still debating myself whether i should buy myself at 4 foot MH fixture or be adventorous and build an LED setup myself.

Thanks. I say go LEDs. You won't regret it. Lots of people are having great success with DIY LED setups.

And just to throw more fuel on the fire I should add that that last review I linked to was a test of the first generation AI fixture. The second generation should perform even better as it uses the latest Cree XP-G LEDs that have higher output than the SSC ones used in the first gen fixtures.

Played around lowering the fixture and found that the colour blending and overlap of the emitters wasn't great in the upper portions of the tank with the lights 3 inches above the water. PAR was between 550 and 600 in the upper part but stayed at 500 in the middle of the tank and was close to 400 at the bottom. I think that to get optimal blending of the light from the emitters and good overlap 6 to 7 inches above the tank is about as low as I will want to run them.

What are you planning for livestock? SPS, LPS, clams, zoa, softs... etc?

yup, I did, and I have no doubt that if Ron put 40 degree optics on his fixture, at 3" he would blow away my MH. and just to add to it my MH were unusaualy high output which was a combanation of the right ballast, my own design for the reflector and good bulbs. in the 25 MH setups I tested the only one that came close was a 400 watt sona agro ballast running iwasaki 6500K bulbs and it was still only slightly over 800.

so I can safly say that a good LED set up such as Ron's will blow any T5 out of the watter, most 150 watt setups, and some of the 250 watt setups. if he would have gone a little tighter spacing which allowed for 40 degree optics with out spotlighting I can say you would be hard to find a MH system that would be a higher output, and it would be pointless to try as at that output level would it realy matter?

Is this because you spent to much on your T5 set up and are haveing buyers regrets Andrew? :mrgreen: don't worry I spent close to 10K on lighting in 2 years befor I found something I was happy with myself. now I did recover some of that selling reflectors and reflector material, but still spent way to much on lighting.. thats why the new tank is going to have LED lighting, as it will give me the ability to change color K value on a whim, and also talyor the intensity to what I have in the tank at the moment. if I get a bunch of new frags, I can dial it down and have it increase slowly over a week or two to prevent bleaching. I can have a gradualy sunrise/sunset instead of a two stage on/off. plus the most fun is building the stuff now keeping the tank going.. maybe I should just build systems for people who want a tank but dont want to build it :mrgreen: then I could just keep on doing the fun stuff .

Steve