You state “I think you can rest assured that everyone in this thread knows what you have posted already... you pretty much just walked into the car dealership and told the salesmen what kinds of cars they sell with that last post.” With no malice intended, I guess it would be useful to provide some information for the car salesman. Sorry, JUST couldn’t avoid saying that. It is truly with positive intent that I suggest the following.
You state “As you will see from that last article, your suggestion of a CIE chromaticity (not CCT) of .31x.31 isn’t on the market. And CCT is something different, not given by coordinates like you gave.” Dominant wavelength is derived from the CIE 1931 Chromaticity diagram and represents the perceived color. CIE1931 was the panel that established standards in the year 1931, and CIE ratings are based on CCT coordinates. Attached is a manufacturer’s chart for CCT for LEDs. The bin number is to be able to order the product item you want. Note that particular CCT coordinates indicate different Kelvin. Consider what the coordinates are for a 20,000 Kelvin light source.
I have to attach the file to a separate post since the size of the file is to big!
You state “Lumens are used to give the total output of a bulb, its not used to describe light across a surface... that would be Lux or Foot candles.” Well… a foot candle is the same as a lumen – 3 foot candles is equal to 3 lumen. I stated “The real question is whether the coral is getting enough light - lumen. At sea level, the sun provides about 2650 lumen per square foot.” I am not suggesting anywhere that 2650 lumen be used at water level in a tank. If you search my other posts, you will find I suggest lower lumen levels for a tank. I simply provided 2650 lumen as a reference point of what the sun does.
You state “So we stick with PAR, or PPFD. 2650 lumen per square foot isn’t really a guideline we can use, neither is 1800 MicroMol/m2/s.” My point was “You have to be careful about lights that achieve high PAR by boosting the violet/blue spectrum at the expense of the rest. A balanced spectrum is needed.” For clarification I mean that high PAR can be achieved but by loading on violet/blue light and not paying sufficient attention to the rest of the spectrum. You have to look at PAR combined with light brightness (Lumen) to create a better aquatic environment. I am sure you have seen high PAR ratings which produce very dim lights. The light output does not provide enough spectrum or lumen to other corals that live higher in the water column.
Your statement of PAR drop-off is correct since there is an inversely proportional relationship between light and distance. You raised this question and I do not know what or how I should respond, but I will it a try based on what I believe you are trying to point out. I repeat – I do not suggest 1800 MicroMol/m2/s at water level unless you have Elkhorn coral or similar ones that live right at the surface. The amount of PAR you get at different levels within your tank is dependent on the output and distance of the specific bulb from the water. Please direct me to the peer reviewed research that specifies “max of 700 for some yellow porites”. The amount of PAR needed at any depth of a tank is dependent on the needs of the coral in that particular tank. John H. Ryther from the Woods Hole Oceanographic Institute did academic research on plankton. Given that plankton have the same kinds of algae (Cholorphyta and zooxanthelle) as corals, he found that "Saturation intensity of Cholorphyta and diatoms for photosynthetic purposes was reached at 500 to 700 foot candles (foot-candle = lumen/square foot) and for dinoflagellates at 2500 to 3000 foot candles. Photosynthetic activity for dinoflagellates (zooxanthelle - algae also) was reduced by 20 to 30% at intensities 1000 foot candle higher". Ryther however, did not specify depths at which photosynthetic inhibition occurred. I believe this data came from laboratory research.
You state “Many tanks have PAR levels of over 2000 near the bulbs if halide (very concentrated light output), or 900 if a tube (T5s). These levels drop off to less than 1000 at the water surface usually, unless you have a very tall tank and need very intense halides (400s) to penetrate to the bottom. Under the surface, light levels usually are 500-600 at most in the first few inches under the water, and often 200 or less at the sand. So where are you getting this '1800' from?” The PAR level of 1000 at water level is accurate in my survey of light output. MHs are raised to avoid heat transfer and so the PAR and lumen output drop significantly. As an aquarist, that should really matter because the advertised PAR or lumen is not what you are getting at the water level. A quantum meter costing $US200 to measure PAR costs would help identify exactly what PAR you are getting and I strongly endorse it as a useful instrument. As to where I am getting the 1800 MicroMol/m2/s, it comes from taking the “perfect” conditions (2000 MicroMol/m2/s) that you refer to at sea level and account for haze and cloud cover:
http://www.wsws.org/articles/1999/jun1999/pollj30.shtml) and (
http://earthobservatory.nasa.gov/Study/ArabianSea) to arrive at 1800 MicroMol/m2/s. It really is more like 1700 MicroMol/m2/s, but I found many lens use to protect the bulb reduce output, so I propose 1800 MicroMol/m2/s to be safe.
Please feel free to raise any other questions regarding my posts as I do enjoy talking about lighting.
Regards,