PAR value and lighting source 10/12/04
Can you please tell me what PAR value is when it comes to lighting? How does it change with Kelvin and how does it change when comparing PC to Metal Halide??? Thanks Jeret
<Wow!  Not such a simple question.  PAR is Photosynthetically Active Radiation.  The chlorophyll in zooxanthellae can only use certain wavelengths of light.  While measurements like Lux or lumens measures total light output, PAR measures only that part of the spectrum that is useable for photosynthesis.
Since PAR depends on both total intensity and spectrum, it is very difficult to generalize about different light sources and unfortunately, manufacturers don't tell us what the PAR is for their lamps.  Authors like Sanjay Joshi and Dana Riddle have done excellent work to report the PAR values of different lamps and light sources.  Google searches on their names will lead you to their work.
Some generalities can be made...  Watt for watt, cooler (bluer) lamps tend to have less PAR than warmer (yellow/red) lamps.  This is because so much of their energy output is concentrated in a narrow band, while warmer lamps tend to have output over a wider part of the spectrum.
It is hard to compare between Fluorescent and MH since the spectra can be quite different, but both technologies produce a similar amount of light intensity per watt.  In other words, 400 watts of fluorescent produces about the same total light as 400w of MH, it is just more spread out.
Many aquarists forget that they can use much less light if they use it more efficiently.  Using carbon or ozone to maintain water clarity, using highly efficient reflectors and keeping them clean and running lights as close as is safely possible to the water all will dramatically improve the amount of light that reaches corals.  Following these practices would allow many aquarists to use significantly less light to achieve the same PAR reaching their corals.  FWIW, PC lamps have an inherent inefficiency since they are constructed of two adjacent tubes.  A lot of the light from each tube shines into the adjacent tube instead of being reflected into the tank.  Best Regards!  AdamC.>

Light Meters 3/30/2004 
Anthony: I am interested in a light meter to measure the various areas in my tank. I have a few goals in mind: 
1) measure values over time to document life and approximate replacement needs of MH bulbs; 
2) get a better idea on dirty lenses, yellowing water, etc. and their influence; 
3) approximately judge the values that my inhabitants do best at when it comes to compensation, saturation, etc. 
<it will help you to do all of these things and more> 
Do you think I should get a PAR meter, or would a LUX meter do? 
<the PAR meter is a slightly better measure for us> 
I don't think I mind the extra cost for a PAR if it is truly the best way to measure for these purposes. 
<yes> 
I have seen PAR meters for $300 and up, and LUX for around $75. Any guidance is appreciated. 
<good things are seldom cheap and cheap things are seldom good ;) Have you looked at the PAR meters from Apogee? Very nice units and popular with aquarists> 
Thanks, Rich 
<best regards, Anthony> <<Or borrow one from a club or retailer... RMF>>

Lighting/Lux meter 2/8/04
I would like to comment on a practice that has worked for me and am wondering why it is not more widely used. Most of the problem with lighting today I feel has to do with intensity, or lack thereof, than with the quality of light spectrum. Many bulbs today have excellent spectrums and you can educate your self on this point fairly easily. Its getting the right intensity on the different unique organisms that is tricky. I have found using a light meter to be extremely useful in this regard. The naked eye is a horrific judge of exactly how light or dark an area of a tank actually is. A method I have found works well for me is when I go to the local fish store I bring my light meter and a gray card with me. I simply place the gray card next to the coral I am interested in and take a light measurement. This gives me a general idea of how much light acclimation will be involved from there tank to mine. If the coral seems to be flourishing in there tank will probably put it in a similar metered area in my tank. Also, when replacing bulbs you can take a measurement before and after the bulbs have been changed to see how greatly your light has fluctuated. Generally when acclimating I always start with one f stop below what ever light they were under before and work up just to be safe. It is also frustrating when you talk to someone who has many species in their tank and all they can tell you is how many watts are in there overhead lights, this gives you no real picture of how much light is getting to the coral because the intensity of light can fluctuate greatly throughout a tank depending on its design. Also, you naked eye is a very poor judge on exactly how light or dark your shaded areas are( they can be vary deceiving). I know corals are able to adapted to many lighting schemes but I think as a whole we could be more accurate as a hobby in keeping light level parameters that are more accurate than the ones presently used. You can get a good light meter for $100 dollars or less and given the expense of the animals and other equipment in the hobby I don't know why they aren't used more. You can take reflective measurements through the glass or you can put you meter in a heavy duty Ziploc bag and take ambient light readings. I have lamented that mail order houses can't give you a light meter reading on the amount of light hitting the coral you will purchase in there tanks. Also, its so much more accurate than bright, somewhat bright, somewhat shady, or what ever those vague terms mean. Hobbyists could pool there readings and set up parameters for corals that where quite a bit more accurate in my opinion. Thank You Greg Kirton
<thanks you very kindly for sharing your thoughts/experiences, Greg. They will be duly posted and shared for all. Best regards, Anthony>

PAR Index or Table?
Mr. Fenner and the WWM Crew,
<cheers>
For as long as I've been reading your articles about lighting captive reef environments I've noticed the same response in many threads:  "...if you only had a PAR meter..."
<they are quite handy... observing trends in coral health, color and vigor... influences of water clarity... aging of lamps, etc>
I've invested in a PAR meter (from Apogee Instruments, $300 with sensor, apogee-inst.com)
<yes... very fine>
and have been startled at the remarkably low readings I was getting on the 2 x 250W MH setup I was running on my main tank.  
<do consider/realize how severely water clarity and lamp cleanliness (dust/salt spray, etc) significantly impact light delivery. Unless you are using ozone or changing carbon weekly... plus cleaning lamps and canopies weekly... you can expect to lose a measurable portion of your light>
In fact, the distance between surface PAR in the wild (2000) and what I was getting just a few inches below the surface in my tank (500) was shocking enough to push me into 400W lights (now getting 1500 at 6"...)
<Hmmm... if you are keeping shallow water species only... perhaps the 400 watters are warranted. For most aquarists, they are not>
My question is this:  while in most cases (excepting aposymbiotic corals of some species, and deep-reef Corallimorphs) "more is better" in the case of light,
<Yikes! You won't catch me agreeing with that startling admonition. It's not even close to correct. More is not better at all... under-lit corals can be supported with feeding... but over-lit corals can/will suffer photo-inhibition and shut down in time. It's best to offer enough light to satisfy the maximum tolerance of your lowest common denominator and feed all other species to compensate>
are you aware of any good references to the range of PAR various animals require to survive-thrive?  
<much field data in the academic archives... Alf Nilsen has published some in the hobby literature (Aquarium Frontiers for one as I recall... hmmm... Acroporas by species in Winter 1994 part 2 peeping at my bookshelf here)>
In other words, while a Montipora capricornis may get "moderate" lighting in guides about it's care, does that mean a PAR value of 100, or 1000???  Is a shallow water species of Acropora meant for a PAR of 750, or 1750? I appreciate your input on this vexing subject.
Thanks, Sean MacKirdy
<like RedOx... PAR values are guidelines not rules... there are many other considerations in captive coral culture. Track an study... do enjoy... but don't get too obsessive about it, mate. Kind regards, Anthony>

Science or Hobby? Marine Lighting - 8/14/03
Great website, lots of great information.  I've read the Marine Lighting primer, other articles and threads, but I can't seem to find any comments on a situation similar to mine).  I know others are looking for this info so I will gladly pass it along!
<a great attitude my friend>
I have a 18 gallon tall with an eclipse 1 hood.  I've retrofitted it with A SmartLite (32W) from Custom Sea Life.
I have a deep sand bed (about 4 inches) and 30 lbs of live rock.
Is there a way to quantitatively describe the lighting at various depths? e.g.) SmartLite 32W - X PAR, Lumens, or Watts at depth Y
<as a useful measure to aquarists, yes... PAR.>
Or better yet an expression for intensity as a function of depth (e.g. I(d) = Io * e^-kd  when d=depth ?
<regular readers of the daily FAQs will know that I have little interest, if not outright disdain, for overtly anal exercises in mental masturbation that far surpass a sound academic or scientific curiosity. I will tell you, Jeff, with a mixture of humor and sincerity that any such discussion regarding the measure of usable light at depth for corals is staggeringly moot in an 18 gallon aquarium. Arguably, it is just as moot in our 24 and 36" deep aquariums when the subjects/objects of our study and admiration (symbiotic reef organisms at large) found over a much wider range in the sea (many species commonly occurring in niches separated by 40 or more feet.>
Can we then relate this to species requirements (compensation and saturation points)?
<it can be done, but cannot be fairly extrapolated by species for the above reason. We do not know where on a reef a given specimen was collected: Acropora formosa in 3 feet of water... or A. formosa from 60 feet of water? Doh! The best we can do with such data is on a specimen by specimen basis IMO... or, with further study to know the range of tolerance and adaptability for a given species. Now that would be useful!>
Is there any published data?
<field data yes... do pillage the academic archives. In aquaristic terms, however... little is available. I do recall Eric B chatting about it. Dana Riddle and Sanjay Yoshi are also very interested in such issues>
In the final analysis, given those parameters, what corals can I realistically expect to grow?  
<ahhh... in an 18 gallon aquarium? Well... there are many many adaptable cnidarians that will grow well in such shallow water. Finessing light is not your problem, Jeff... controlling growth will be your reality! Dude... do consider installing a beer meister next to your reef tank. Either that, or convert a Kalkwasser doser into a heroin drip. Just a suggestion. Best of luck! Anthony>

How much light is enough?
Ok, second question today/tonight.  I very much appreciate the service that you are doing for your fellow (and usually less experienced) aquarists.  It says a lot about a person to put up with, and answer so many questions from strangers regarding tanks you have nothing to do with!
<Our pleasure!>
Anyway, to my setup and question. . . I am building a 70 (18" tall I believe) gallon reef tank.  I will be using an EV-120 skimmer, and supplementing/buffering as needed (how is undecided yet).   The tank will be home to leathers, polyps, and mushrooms, and some hard corals including a hammer, and open brains.  I believe that the toughest thing I would like to incorporate is a maxima clam.  After reading over your lighting FAQ's, I am confused on how to size my compact fluorescents for the tank.  My main goal is NOT maximal growth, it is good health of the animals, and enjoyment by me!  
<Yes...not mutually exclusive, in fact, one in the same. Maximum health equals maximum growth.  Any less is less.>
I  was planning on going with a CSL 4x96w fixture.  Should I go with the original plan, or would a 4x65w fixture be better if my goal is not maximal growth?  
<No, with a maxima clam you need the intensity of the higher wattage.  A clam will still need to be placed at or near the surface of the water.>
Also, I definitely want to run the front right and left bulbs actinic, and the rear right and left 8800K or 10000K.  Does this combination of bulbs play any role in the decision?
<No. I would recommend as even a mixing of bulbs as possible for even light coverage.  50% 10000 and 50% actinic blue provides a good balance and pleasant appearance.>
Thanks once again, Your confused friend, Scott
<Hope this clears your head my friend!  Craig>

Lux Meter
Hi, I have a question about Lux meters. If I purchased one, I could get Lux information for different levels in my tank.
How could I put this information to good use? Is there something that tells me, you need "x" amount of Lux for coral "a", and "x" amount of Lux for coral "b"? Most information I read says, certain corals prefer low, medium, or high amounts of light. Are these meters very useful?
<Ahh, not much use for the average person. There aren't really any books or references with Lux recommendations. It's easier to understand what is meant by low, medium, and high and their relation to water depth, penetration and intensity. It's also best to find the best general optimal conditions for the inhabitant in question and acclimate up to that level slowly.> 
Cheers, Craig
Thanks, Angelo

Is Lux the same as lumens (for light parameters)?
<Nope. Please see here: http://whatis.techtarget.com/definition/0,,sid9_gci542011,00.html
Bob Fenner>
Thank you,
Luke

Lighting a 120 Reef
Hi Bob,
This lighting thing has got to be the most confusing aspect of a reef set up.
<It's one of the principal ones...>
Anyway as most people I'd prefer to buy equipment once and would want to be able to keep many different types of coral/inverts. I've read on some web sites that fluorescent light produces as much heat as metal halides do.
<No... not per watt of energy consumed, per light produced... MH much more heat by its method of photonic production...>
They just produce it in larger area and not so concentrated like the halides. In pricing CF and VHO vs. metal halides it appears that watt for watt the halides work out cheaper to set up but not necessarily operate.
<Well-stated>
Also lumens seem very important to coral life and not watts although high lumens means high watts.
<Yes sort of to the former... many stinging-celled life forms need, can use intense lighting... but no to the latter... you can spend a bunch on power (consumed) and not end up with much useful illumination>
Anyway I'm not sure whether heat would be a problem on any of the choices since I plan on putting a 100gal sump in the basement which is about 67 degrees or year round.
<Hmm, perhaps an expensive proposition... you want above all to be able to simply, consistently, inexpensively control temperature... not "pay" to heat up the water in one place, lose the thermal content elsewhere...>
I would think that this might help in a stable temp for the display tank. Which set up would you use ? 2 175 10k & 2 VHO 110 03, 2 250 10k & 2 VHO 110 03 or 4 96CF 10K & 2 VHO 110 03
<For what sorts of livestock? And what purpose? Are you going to culture, sell fragged Acroporids for instance? I would go with the last choice if it were up to me... but many people I know would mix the MH with the VHO actinics... for looks, production...>
or what about the HQI ? Possibly 2 150 10k and 2 VHO 110. I've read at another board that the 150HQI puts out as many lumens as a 250 MH and roughly equiv. to a 300 watt bulb.
<But not useful (PAR) energy at a constant-age rate... don't get involved here>
Sorry to keep bothering you but with endless opinions on set ups its hard to know which road to go. It seems everyone swears by whatever lighting they are using usually switching from another an say I'll never go back to VHO, CF or MH. Thanks Mike
<Many sayings come to mind: "many roads", "to each their own", "if your brother jumped off a bridge...." All these light fixturing possibilities will work... with different up front, continuing costs, looks, heat inputs, biological effects (per your chosen livestock, desires with same), maintenance issues... Make a chart of all the factors you consider important, rank/differentiate them (give them oh so many points each to consider), score the choices per those factors... add up the points per type/choice/mix of lighting. Voila! Go with the highest scored arrangement... then get on to the terror of considering what sorts of filtration you might have... Bob Fenner>
Thanks for your reply. My thinking on the types of livestock would be a healthy balanced mixture from each category of corals (soft, LPS, SPS)/inverts/fish.
<Sounds good... but do investigate these by species... as there is a huge range in light use/tolerance within these groups. Many soft and hard corals are even non-photosynthetic... and other invertebrates, fishes have low light needs. Bob Fenner>

Question?? (re marine lighting "rules")
"Dear Bob": Is there a "rule of thumb" as far as the intensity of light for marine aquariums?? 
<There are a few... with many stipulations... for shape of the system, types of livestock, desires of the keeper...>
<><>From different sources I've learned that between 4-6 watts / gallon depending of invertebrates<><><><>Watts or Lumens????
<Mmm, lumens are a better measure...>
not the same, a 4 watt incandescent than a 4 watt metal halide therefore different intensity, different lumens
<Not different lumens... different amount/quantity per watt consumed... do read over the WWM site, the Net re light quantification>
Please advice on this topic thanks a bunch, and keep them beautiful pix coming please!!!!
<Keep studying my friend. Bob Fenner>