Quote:
Originally Posted by Canadian
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. That's all I am trying to say. I would love to compile 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.