[StirCrazy]

Originally Posted by Canadian

But I have to comment on the PAR. Your old T5 fixture is not a very good comparator for a moderately good T5 fixture. Your PAR values with the T5 fixture are abysmal and not reflective of typical high quality T5 fixtures with 54W lamps (presumably your reported T5 PAR values are with new lamps as well given you're comparing this to brand new LEDs). Secondly, the PAR values with your DIY LED fixture are still quite low. Every time a discussion about LEDs comes up the comparison to 250W and 400W MH is made. These numbers clearly show they aren't even close in the manner in which you've designed this fixture. I've maintained that until real numbers for PAR are measured and reported the propaganda of "equal to a 400W MH" is absurd. So far the data I've seen do not support the marketing BS. In all honesty, did you expect the PAR values to be that low?

And as far as lifespan goes: again there is no long term data for PAR as far as I know (unless you have info I haven't seen yet). T5 lamps have a reasonable lifetime but their effective PAR drops much faster. At this point we don't have any good data to support the numbers being batted around about 50,000 hours lifespan. Sure, the emitter may continue to emit light for 50,000 hours but at what PAR?

Andrew, you have to go do some reading in this thread, he is getting higher par at 5 times the distance. T5 was at 3.5" and he is still getting higher PAR at 17" above the tank, which he did becasue he didn't have his dimming setup done yet. At 8" he was over 500 PAR where at 3.5 with the T5 he was at 300 PAR, Also this is with 60 and 80 degree optics, no one ever said thoes optics will give you 250 - 400 MH levels, it is 40 degree optics you need to get that, the best you will get with 60's is around a 150 watt MH which he is pretty close to as a 150watt mh isn't much higher than a good T5 set up. if you want a good comparason maybe Ron will take a PAR reading at 3.5" with the LEDs then you can see how much more punch he is realy getting, I am going to guess that he will be around 700 at the surface and probably close to or over 400 at the bottom, but thats a guess.

now as for the PAR output, you are thinking along the lines of a gas filled cathode tube. you can't think that way with LED as there is no gas to break down and change the spectrum. it has been showen there is absolutly no shift in spectrum in a LED over its life, only a 15% decrease in intensity, so there is no reason to think other than a 15% decrees in PAR as there will be no spectrum shift to compound the drop as it does in MH, PC, CF, ect. so if we look at that the average MH has a 20% drop by the time it is changed, and most of that drop occures int he first 6 months, floressents have a even steaper drop off, so going with LEDs after 5000 days (10 hours per day) you will have 15% less intensity with no spectral shift so you should not get nusence algae ect..

Steve