It may not be necessary to change MH bulbs yearly

Cheech said:

Check out this article...

http://reefkeeping.com/issues/2007-04/ac/index.php






I'm nearing the 1 year make of my MHs... I'm pretty broke right now, so I think I'll hold out another 6 months or so before spending the extra 200$ on new bulbs.


What do you guys think?

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The scope of that article is too limited to make much of a decision. It is food for thought, though. If you have a PPFD meter, you can plot this for yourself with your own bulb/ballast combo and you can assess whether or not you need to change sooner or later. If you don't or have no means of doing so, it is a good idea to change them out on a regular schedule to potentially compensate for what you can't measure.

fsn77 said:

I'm not convinced one way or the other, to be honest, although I've never taken PAR measurements over time to confirm anything.

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This is what drives me crazy when people use PAR like that.. not attacking you personally, just the line of thinking "PAR reduction means time to replace bulb". PAR is one small piece of the puzzle and is actually a terrible way to measure bulb life. You need a Spectrometer to measure bulb life, not a PAR/PPFD meter. The PPFD meter is going to tell you pretty much the same thing for any bulb.. 18 months before the PAR readings start to decline past 30%.. well.. in those 18 months your entire 400-500nm range has burned up and you are now thowing a bunch of yellow/orange/red light at your corals and no blues.. but your PAR reading, since those colors fall within the PAR scale, will still come out looking good even though the QUALITY of light coming off the bulb is no longer good, and hasn't been for the last 9 months.

Since I overdrive my MH bulbs, depending on the bulbs, I honestly get 30-90 DAYS before the bulb is what I personally consider "going bad" due to spectral shift. PAR readings are within 5% of a new bulb, so the bulb is still good for lighting up your backyard at night, but the spectrum shift has made it not so good for corals IMO.

Cool, I was hoping just because I quoted you that you didn't think I was directing anything towards you.

Shortest way to say it I guess is PAR measurement = Intensity of all combined light within the PAR scale (around 400-700nm wavelength). That is all PAR measurements should really be used for, learning the intensity of your lighting at different areas of your tank so you know where to best place corals.

If more people would get together and take measurements of certain corals and PAR readings and input those into an online database somewhere that would be a huge benefit for everyone. Some corals may have a large range in which they do well (200-1200PAR), others have a narrow range (700-900PAR), by getting a large database from as many people as possible we can learn things like "best coral placement according to lighting". Flow would be a different database.

People just put too much into PAR values.. think there is a magic number they have to reach, or that number is telling you more than it really is. PAR readings are completely different in every tank and they differ greatly just from location in the tank and even how much surface movement you have, so it is a very inaccurate measurement to start with. I feel PAR has become todays "WPG Rule".. people finally learned WPG isn't a good way to measure lighting anymore and somehow PAR became the next big thing to replace that. While it is certainly a more accurate method of measuring the intensity of light than the WPG rule, it leaves a gaping hole when it comes to the question about the quality of the light, it is only telling you the quantity. People then start to sacrifice quality for quantity in the attempt to get the highest PAR reading, which can't be good.

Ace25 said:

Cool, I was hoping just because I quoted you that you didn't think I was directing anything towards you.

Shortest way to say it I guess is PAR measurement = Intensity of all combined light within the PAR scale (around 400-700nm wavelength). That is all PAR measurements should really be used for, learning the intensity of your lighting at different areas of your tank so you know where to best place corals.

If more people would get together and take measurements of certain corals and PAR readings and input those into an online database somewhere that would be a huge benefit for everyone. Some corals may have a large range in which they do well (200-1200PAR), others have a narrow range (700-900PAR), by getting a large database from as many people as possible we can learn things like "best coral placement according to lighting". Flow would be a different database.

People just put too much into PAR values.. think there is a magic number they have to reach, or that number is telling you more than it really is. PAR readings are completely different in every tank and they differ greatly just from location in the tank and even how much surface movement you have, so it is a very inaccurate measurement to start with. I feel PAR has become todays "WPG Rule".. people finally learned WPG isn't a good way to measure lighting anymore and somehow PAR became the next big thing to replace that. While it is certainly a more accurate method of measuring the intensity of light than the WPG rule, it leaves a gaping hole when it comes to the question about the quality of the light, it is only telling you the quantity. People then start to sacrifice quality for quantity in the attempt to get the highest PAR reading, which can't be good.

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Using PAR at face value is close to meaningless. What I meant and recommend is if you look at it in terms of percentages of reduction of intensity. This is in addition to noting whether or not the resulting intensity is sufficient for corals. If used that way, the measure is far more meaningful in terms of useful lamp life. You'd need to plot what bulbs you use and find out when the decrease narrows and eventually stops. That is what we used to to when I worked for a LFS. We had been doing it for a while and it is similar to what was later written in that article. The article is too narrow in terms of scope, however.

I am confused about "quality," however. PAR measurements are what are used in the field and are what biologists largely draw data from--not just for corals, but plants as well. Could you explain what you mean by that? Unless you are referring to the very slight skew of efficiency of utilization of light in the bluer spectra.

Yes, the slight skew, ie, in general terms corals can absorb and utilize 95% of the blue spectrum but only 75% of the red spectrum, so as the elements in the bulb burn with time, the blue will burn out much faster than the red, meaning the more useful of part of the PAR spectrum for corals will deplete faster. In terrestrial plants, from the limited research I have done, don't follow exactly the same absorption levels as corals do. I can only guess on why, that corals being underwater adapted over eons to utilize the blue spectrum more efficiently than the red spectrum due to the lack of reds as depths in the ocean. I understand this is a slight difference here, and those numbers are no where near exact or could be used to generalize every coral, but I feel the blue spectrum does play an important role in coral health.

Also, since PAR readings are only a spot measurement, ie, count all the photons within a range of light and add them up to to give you a number, it can't tell you how many red photons vs blue photons hit at that time of measurement, only the total of all the light in the PAR range. Since Red photons move much faster than blue photons, at a rate of close to 3:1 I believe, that means the PAR reading off the bat is going to give you a skewed reading that leans to the red side already, since 3 red hit the sensor for every blue even though blue is utilized more efficiently. So when the halides that make blue light burns out on the MH bulb after 9 months, even though that isn't much in regards to what the meter will tell you, that is a lot of quality light spectrum you have lost in the bulb.

Say you have a reading of 1000PAR on a new bulb, after 9 months you get a reading of 800PAR, that is a 20% reduction in intensity, but out of that 200PAR loss 150PAR of that came from the blue side of the spectrum. These are just random numbers to give an example. I don't know the exact numbers but I do know what I have noticed on my own tank as my lights get "whiter" with age and corals start to look faded and growth slows down after just a couple months on a new bulb. I have to think the lack of blue spectrum is playing a part in that... Again to stress the point, I overdrive my bulbs to the max so my bulb life is severely cut down compared to normal ballast/bulb combos. I still think 9 months is a good average to recommend to people running electronic ballasts.

Edit: One way to show this with a PAR meter is to take a reading at the surface and at the bottom of the tank when you have a new bulb and then later on. Since the red spectrum will get filtered out with depth the lower part of your tank is more of the blue light then the red light, so in your later PAR measurements the lower readings will have a greater difference between new and old readings vs the surface reading showing you that more of the blue spectrum has left the bulb as the halides are used up.

Okay, but how does that extra efficiency translate into actual usage? Is it appreciable? Is it necessary to go through the trouble? I'm just not convinced, as most of the articles I have read on the subject fall woefully short of a real or even a good conclusion. Yes, corals have a very slight skew toward efficiency with the blue ranges. But why do corals do miserably when there is almost all blue light (the converse is also true), like actinics? Part of the issue is that there aren't enough blue photons available to give a huge advantage to bluer spectral absorption. It takes more energy to output bluer photons than it does other photons, despite the fact that all photons have the same energy (how much of that energy is used is what relates to the efficiency). You can provide more energy in the other spectra due to the fact that these other spectra require less energy to create. That doesn't mean that blue can be omitted outright, as the greatest efficiency peaks will result with application of broad spectra. You get some blue, along with a higher peak in reds, making up for the deficiency in blues . I'd love to see some analysis that looks at the greatest amounts of productivity in corals with different spectra. I have the feeling that broad spectra will beat out both bluer and redder lamps in terms of overall productivity. You can look at any absorbance charts and see that the likelihood is high for this. This, coincidentally, is more similar to sunlight in shallow water, which is what these animals evolved to utilize.

That being said, I think a good number of aquarists are reaching the point that there is almost too much light provided. This is happening a lot more than it used to and it is reasonable, assuming the advances in reflectors, maximizing intensity, etc. This would also explain, much more plausibly than a small edge in efficiency of utilization, that bluer lamps or a shift into bluer spectra, in general, are having profound effects. Basically, the overall reduction in intensity is more likely to blame for the increased growth rates, etc. that many experience now.

In any case, PAR is all light that is available in the most common photosynthetic ranges for chlorophyll. Pretty much all photosynthetic organisms will be able to use at least some of the spectra within the ranges of PAR--corals and plants are no exception. Yes, some of the absorbances will be slightly different (mainly due to accessory pigments, etc.), even between closely-related species, but the overall range is pretty standard across the board, which is what makes it such a useful measure.

Edit: In all, while I always support further research into anything, I think that aquarists overthinking the findings and applying them outside of their contexts. Not purposely, mind you, but I think it is fueling a good deal of misconceptions (and the consequent head-banging, hair-pulling quandaries that often pop up). I think we've arrived at a point where lighting is as efficient and efficacious as it needs to be in terms of providing the maximum intensity necessary (and then some), honestly. Sure, new ways of providing that will pop up, but I don't see any huge advances in terms of providing actual light making that much of a difference. I think there are more areas that could be of even greater benefit to the knowledge pool for coral husbandry (deeper understanding of individual species' actual lighting needs, nutritional requirements, foods, etc. seem a likely candidates). JMHO.