Derek Posted June 21, 2002 Report Share Posted June 21, 2002 Pegasus wrote: Back to the question, There is obviously a formula for watts per depth of tank, per period left on, (W X D X T= ideal condition) Quote Link to comment Share on other sites More sharing options...
Pegasus Posted June 21, 2002 Report Share Posted June 21, 2002 Thanks Derek, great site the Krib.... lotsa useful info. Will add the link to the list. (Tech/Useful Links) Quote Link to comment Share on other sites More sharing options...
Warren Posted July 14, 2002 Report Share Posted July 14, 2002 I'm currently working on a lighting article for the Aquarium World. In it is a formula for roughly calculating the watts required. Interestingly, it is not actually the watts that matter. It is the lumens and colour spectrum. If a lamp has a higher lumen value and the correct colour spectrum peaks, it is more effective. Therefore a less efficient lamp or one with a non ideal colour spectrum will need to have more watts. This however can lead to algae as the excess light in the incorrect colours can promote it. The relationship seems to be fairly closely related to surface area as seen in the link by Derek. However it can be seen that the general trend on the graph is flatter than the lines for watts/surface area. It seems that depth has some small bearing on the lumen requirement as water absorbes certain colours faster than others. So, watts required are approximately equal to lumen requirement/lumen output for the lamp. Lumen requirement is proportional the surface area x a depth adjustment. I will post the article to the fishroom 'articles section' after it is released in the Aquarium World. Quote Link to comment Share on other sites More sharing options...
Derek Posted July 14, 2002 Author Report Share Posted July 14, 2002 Gotta agree with most of what you say Warren, including the fact that depth obviously has a bearing on how much light you need above the tank. Assuming it is not going to impact on your article would you care to comment on the following. There is an old (1973) TFH book (Light in the aquarium by Rolf Kubler, Catalogue Number PS-301) which goes into the relationship between watts, lumans, surface area and depth. Basically the equation is N = (ExS)/(24xd) Where N=answer in Watts E= desired lux at bottom of tank S=surface area in square meters 24 is a constant ( the author does not say how he derived it) d=wastage factor dependent on water depth (d is obtained from a table in the book) i.e. at 20cm d=0.82 at 60cm d=0.55 Of course certain assumptions are made: 1. The water is almost colourless, no peat filtration etc. 2.The cover glass is clean 3.The reflector is of good quality. Although this seems very detailed it still leaves you effectively choosing the watts because you have to guess the correct light intensity (lux) that you want at the bottom of the tank. Any change in this guess, changes the "calculated" watts. As such I have always felt this formula loses its usefulness. It appears to me that some rule of thumb such as X watts/litre is the best we can ever hope for, as much as I would like something better. What am I missing here? Quote Link to comment Share on other sites More sharing options...
Caryl Posted July 14, 2002 Report Share Posted July 14, 2002 Here's a silly question. I know plants need light to grow but do they need the same light at the top of the plant as at the base? My tank is a bit deeper than the norm but the tops of the plants are certainly a lot closer to the lights than the bottoms. It is the tops that grow usually so does it matter if my light is not enough for the depth? My plants are certainly growing and I have Anubias nana and mini vallis growing ok at the lowest levels. The red rotala has been taking off lately and I am trimming it almost weekly. Quote Link to comment Share on other sites More sharing options...
Derek Posted July 14, 2002 Author Report Share Posted July 14, 2002 Good question Caryl. It is not something I have ever thought about before, so my answers are just musings on my part. They may or may not be correct. Plants not only use light for photosynthesis. They also need light to synthesise chlorophyll. Fortunately they use the same wavelengths for both, mainly in the blue and red parts of the spectrum. In the green-yellow part of the spectrum some photosynthesis can occur but very little cholorphyll synthesis takes place. Another requirement for the synthesis of cholorphyll is iron. Iron is one of those nutrients that the plant cannot translocate from a store in one part of the plant to another part. If there is an iron defficiency new leaves look white or translucent due to a total lack of chlorophyll. In contrast magnesium is a nutrient that can be translocated. This is why a sign of magniesium defficiency is yellowing between the veins in OLDER leaves. The plant is moving magnesium from the older leaves to the growing shoots. So I guess the plant itself considers the growing tips more important than older established leaves. The growing shoots must have sufficient light intensity of the correct wavelengths to produce chlorophyll. The lower leaves that are shaded by other plant leaves will receive a greater proportion of their light in the green-yellow part of the spectrum as the leaves above them will have absorbed some of the other colours. However these leaves will still be able to use this light for photosynthesis. Although photosynthesis will not be driven anywhere near its maximium rate under these conditions. So to answer your question I would say that all parts of the plant need sufficient light to maintain good health but it is the top or growing shoots that require the most. Another way to put it would be insufficient light at the base of a plant will not kill the plant but insufficient light at the top of a plant will. Different plants require different amounts of light which is why your rotala is growing well at the top of your tank and not so well at the bottom, while the Anubias and the "mini Val" (which is probably a sagitteria species) are doing OK in less intense light at the bottom. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 17, 2002 Report Share Posted July 17, 2002 Sounds like a good book Derek. Wish I'd known about it earlier. Is it still available? I want to try to get my article as accurate as possible so it does not have to be edited too often. I've just had a reply to my glass thickness article telling me I made a mistake in the formula. Just the typical typo type stuff, - a bracket in the wrong place or an extra '0' sort of error. Its no major, but I will be editing it soon to fix it up. Good that someone picked it up however. I like feedback of this sort, it helps keep you on your toes. The information I've gathered (and worked out) is pretty much along the lines of what you've suggested. The constant 24 will be replaced by a variable in my findings and it will have some bearing on the colour spectrum of the lamp. The d (wastage factor) is what I'm currently stuck on. Trying to correlate the effect of colour loss with depth and the effect it has on the plant. Initial colour spectrum and effect on depth are inter-related however... hmmm. Caryls question is interesting. Does a low light plant do well at the bottom of a deep tank with relatively bright lights, or in a shallow tank with soft lighting. In both cases the plant will receive approximately the same brightness of light, but completely different colour spectrums. Also what is the effect on stem plants in deep tanks. I know in my own tanks, the red plants are redder at the top and more faded at the bottom. Is it related to light intensity or light colour? Hopefully I'll have all the answers in the article. Quote Link to comment Share on other sites More sharing options...
ajbroome Posted July 17, 2002 Report Share Posted July 17, 2002 Warren said... > Sounds like a good book Derek. Wish I'd known about it earlier. > Is it still available? I've got a copy if you want to borrow it. Andrew. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 18, 2002 Report Share Posted July 18, 2002 Thanks anyway Andrew, but I've already got another offer. Cheers, Warren Quote Link to comment Share on other sites More sharing options...
ajbroome Posted July 26, 2002 Report Share Posted July 26, 2002 Warren... > Thanks anyway Andrew, but I've already got another offer. While shifting stuff the other day, I re-found a book called "Artificial Light in Horticulture" by A. E Canham. It was published in 1966 but has some good info... Andrew. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 27, 2002 Report Share Posted July 27, 2002 Hi Andrew, Cool, could I borrow it please? The book Derek sent me is full of goodies. Mostly a lot I'd already learnt, but it reinforces most ideas and introduces a whole bunch of new things I'd not thought of. If your book is even half as good, it will help a lot. Regards Warren. Quote Link to comment Share on other sites More sharing options...
ajbroome Posted July 29, 2002 Report Share Posted July 29, 2002 Warren said... > Cool, could I borrow it please? Sure. Drop me a line ([email protected]) and we'll sort something out. Later, Andrew. Quote Link to comment Share on other sites More sharing options...
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