PUR vs PAR in LED's

[seabass1]

I got rid of all my LED fixtures because I wasn't sold on the effects of LED lighting on my livestock. I bought a nice T5 6-bulb fixture & everything is doing very nice again.

I've also noticed so many members getting rid.....I mean, selling their fixtures. So, ever since, I've been trying to get to the bottom of the LED craze.

If PAR is the amount of light given off in a certain wavelength & PUR (Photosynthetically Usable Radiation) is the total usable available light, isn't it misleading to measure in PAR rather than PUR?

I found only 3 or 4 reputable LED companies building fixtures that are worth a darn! Anyone else looked into this????????????

[seabass1]

Nobody.........Anybody?????????

[laffingcrow]

If everything is doing OK now with T-5s... what bulbs are you using?
I've noticed that many reefers use a pink/purple T-5 with the usual actinic blue with very good results.

If PAR is the amount of light given off in a certain wavelength & PUR (Photosynthetically Usable Radiation) is the total usable available light, isn't it misleading to measure in PAR rather than PUR?

Great question but the answer is in the details... The short answer in NO, PAR is not misleading; it's just that there is just so much more to know and when did a company trying to sell a product tell you all the facts? If you were marketing a product you too would highlight what you have not what you don't?

PAR is necessary to know how bright your light is, as so many LED fixtures are way too under powered for what some want them to do.
So PAR is extremely important to the health of corals and one simply cannot tell by eye how bright your fixture is.

How to determine PUR?
Even the so common China fixture using white and royal blue can sustain a lot of corals by having enough PAR but not ALL corals because they fail at having enough Photosynthetic Usable wavelengths available for the individual components of chlorophyll? Coloration will fade in time and or the coral will melt away.
I believe many have experienced this with older two color LED fixtures and are shifting away from them.

PUR starts to get more specific to the needs of individual corals and since discreet wavelength lighting (LEDs) are so new it's hard to find data to support that inquiry but much of the industry is now turning to fuller spectrum fixtures.
There is much controversy regarding whether to use red in the full spectrum fixture
as too many only have white LEDs and Royal Blue LEDs with a trend now toward neutral whites instead of cool whites to pick up a little more red wavelength available in that color.

There is less controversy over more wavelengths from 400nm - 500nm
Most manufacturers are putting in as many different wavelengths as possible in this range since this is the range that benefits coral growth the most.

So my question is what species of Zooxanthellae live in what species of coral and what wavelengths does one need to approximate the needs of each coral regarding photosynthesis? (I've got links to graphs and charts if that would help?)
Until one can answer those questions scientifically it will be a shotgun approach with a lot of hearsay backed by trial and error? In the mean time I think the market is there to drive innovation and I hope the era of off the shelf manufacturing of reef LEDs is nearing it's end.
My belief is the future in reef lighting is going to be more like the full spectrum dream chip with all the discreet wavelengths (customizable) in one tight cluster to give sun like shimmer similar to a single halide.

I can imagine different size units that can scale up from nano to large reefs with all the units linkable and controllable.
I'd like to know what others have found or experienced?
Brian

[MustangBill]

You bring up a lot of good points, I had a 12 bulb T5 system that I was happy with and all of my corals were doing to great, I switched to the 50/50 blue white LED's with out much noticeable difference, it has since been a year with those LED's I think now my corals that are closer to the bottom do not look as good while the corals closer to the top are doing ok, not as good as they were under the T-5s. Which I think is where the PAR factor comes in for depth penetration. I recently installed a full spectrum cannon on one side of my tank about a month ago and I can already see a difference in those corals on that side as far color, light penetration and shimmer. As laffingcrow said the shift seems to be more toward full spectrum. Only time and research will tell but so far I'm liking it.
I think the biggest reason most people switched to LEDs to begin with is that the blue was so strong it made your coral colors pop but took away (unknowingly) the PUR part of the equation which in my case seemed to be a little bit detrimental.