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[APD] light variabilty
" The amount changes
over time with any scaling or etching that occurs, and the
bulb degrades over time too. You can run the bulbs a little
longer to compensate, assuming you're running them for only
about 10 hours or so per day to begin with. Or you can
start out with a little bit more light than you might
otherwise figure -- or you can start out with a lot more
light but keep some bits of Ceratopteris cornuta (water
sprite) floating around the surface to act as a light
buffer -- the amount of T. cornuta is easily adjusted ;-)
with pruning -- or you can just accept the amount of light
you get with the set up. If the plants aren't asking for
more light, I wouldn't let the math override their
contented silence ;-)
This is the point in the variability using watt/Par rules, the light declines with time due to such things that Scott listed below and given all the user variation (see just a few below). Even if you came up with a better rule theoretically, these variations will not change and are more significant than the rule itself.
It is therefore prudent use another method that accounts for light variation over time.
Thus good CO2/nutrients that account for any light level above the minimum.
Doing so allows for light to be used at max efficiency at any practical light level.
The results of this approach to all lighting levels above the LCP has shown to be highly effective.
This circumvents the need for a more accurate rule than w/gal.
If you use the old car analogy for lighting, the faster you go(the more light), the higher the gas use(more nutrients/CO2, $ for electric) and wear and tear on the car. You also run a higher risk if you crash or something goes wrong at higher light intensity. As long as you are moving forward, then you can go at any speed (which is a good assumption to incorporate if you use a rule or wish to test lighting). If you can drive 150mph, you can easily drive 25mph. 25mph is safer, better milage, but some find it boring to go so slow.
The data already exist for w/lumens efficiencies for a variety of lamps. You can use a generalized ratio to compare PC (take the average of several brands etc), MH's (again take the average of several types) T5's, VHO's and compare them to NO averages.
The difference can be used to add a ratio factor.
Say 2w/gal is ideal for a 55, with PC lights, you can use 1.5 w/gal since they are more efficient (use a .75 fudge factor for the NO when using a more efficient bulb light PC's etc).
A simple table of average differences from the bulbs types can be used.
Quartz MR16 DC 12v have a lumen rating of 17lumens per watt, so compared to NO FL's, you'd look at about 4.1, so you'd need 450 or so watts for a 55 gal tank to get the same lumens.
Most new folks will not need to do this, but the more advanced user can do this and look this data up easily and come up with a fairly good estimation that Jerry was sugegsting.
See the link:
Seems like plenty of empirical evidence and something that requires far less WORK for the same result goal. It's things like this that can show you do not need to run off and do lots of testing and work all in the name of knowledge when you can use the knowledge you already have but..............consider what your goal is and the what you hope to achieve in doing the work. Often there are ways that will answer the question without the huge work load nor do they need to be direct measurements.
I suppose I can run around with my light meter and test my tanks, and other folk's and log in every bulb type, water depth, lighting time, staggering routines, sunlight influx vs artifical light infux, reflection from the glass/acrylic, bulb age, whether they have low lying plants, plant species, glass lids or not, do they keep the bulbs clean and free of lime/marl, do they maintain non limiting CO2/nutrients, where and what angel is the measurement taken(you will need to take several over the area in question and at various depths) etc.
But..........I'd rather not..........just to improve the w/gal rule. any one of these things might be overlooked, and they may be much greater than the difference between watts/gal and PAR/gal.
I do not see a significant gain from this. If you do, have at it, but you need to address at least the issues I just listed. Simply making sure the nutrients/CO2 are non limiting will be a significant challenge.
I can do this experiment and know how to do this, but unless I'm getting paid or the issue is really a burning question it's not going to happen........but I'm not suggesting that someone else not do this, personally I'd rather go Mt climbing.
I've seen *many folks* propose all sorts of in depth light studies etc over the years, when I say do it yourself if you feel it's significant, suddenly we no longer hear back from them and they ignore the issue. Seems they want other folks to do the work.
Arm chair aquarist talk a lot, but do little if any research.
My advice: if you feel strongly about something, do the work yourself and see what things you might be overlooking before going about it. Nothing is worse than spending 2 years, $$, effort and then spacing out a major significant confounding factor/assumption.
Those are the things you will want to look into before proceding.
I gave folks a simple way to better hone the w/gal rule to account for many bulb types, Daniel has provided the list and has also done the work along with others.
This improves the w/gal rule for the more advanced folks which was the goal of Jerry's but without scraping the PAR. This allows the rule to use for new folks and slightly modified for the more advanced user pushing the limits more. It does use Jerry's original idea of PAR.
The best of both worlds.
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