jewels Posted June 9, 2011 Report Share Posted June 9, 2011 I have been very curious lately about delivering light into aquariums. Specificly - how much light is being supplied in relation to how much ( intensity ) actually reaches the substrate. I have a homebuilt half gallon nano. It is fitted with a DIY LED fixture. This thing is chockablock with naja-grass. Under this gastly canopy I measure 2.0 units, , , Two units of what ? To determine the PAR (Photosynthetically Available Radiation) I measured PPFD (Photosynthetic Photon Flux Density) at the substrate and it turned out to be 2 microMol/m2/sec @ a depth of six inches. I will call this 2 PAR (because its a shorter acronym & I won't associate it with a lifejacket) So, next I wonder just how much light could I put down there if the plants did not obscure the light ? Easy enough to determine - just tug it all out and measure again. With the plants out my reading shot up to a surprising 35 PAR. :shock: Espresso'd as a percentage . %95 of the available light never made it to the compost . Alterantively . The aquarium was 17X brighter without the plants. I did not play with this sensor for very long before I began to realise there are many things we I assume are going on in there that are actually just not happening. The numbers I posted above are the only ones I recall from memory @ the moment. I will post more observations from my data @ home. A few things I have learned so far. Light diminishes exponentialy when diffused/ obstructed. A layer of duckweed can reduce PAR by more than %50 A good reflector can direct 50X more light than without. The human eye is absolutely useless in judging PAR intensity. Quote Link to comment Share on other sites More sharing options...
ubr0ke Posted June 10, 2011 Report Share Posted June 10, 2011 Are you using a lux meter or a par meter? Quote Link to comment Share on other sites More sharing options...
jewels Posted June 10, 2011 Author Report Share Posted June 10, 2011 Apogee SQ-120 sensor Quote Link to comment Share on other sites More sharing options...
jewels Posted June 10, 2011 Author Report Share Posted June 10, 2011 Where'd the cheese go ? These measurements are from a 20 Gallon - twelve inch deep aquarium with a moderate amount of duckweed cover @ 12" 20 PAR@ 6" 40.5 PAR@3.5" 67.5 PAR When I removed all weed I get @ 12" 38 PAR@ 6" 68.5 PAR@3.5" 162 PAR Immediately under the duckweed ( 3.5" from the bottom of reflector) I got only 67.5 PAR. By simply removing the weed the value went up to 162 - HUGE improvement ! Consider there were other factors involved. The tank is "well" planted [30-40 % of the foot print has a canopy within two inches of waterline]; readings @ the compost were still reduced due to shading from other plants. By trimming ( the volume - not overall height) I was able to increase the PAR @ the substrate up to 51 PAR. Original reading @ substrate 20 PAR After removing weed and a little trimming 51 PAR With a little housekeeping I was able to more than double the amount of light delivered to the substrate. With a better reflector I could triple it again. Quote Link to comment Share on other sites More sharing options...
jewels Posted June 10, 2011 Author Report Share Posted June 10, 2011 I have no 'mad graphic skillz' so a little imagination will be required. Imagine , , , a broccoli :chair: sorry best I could do I have a lovely mound of Rotala and for it happens to cast an identical shadow as a crown of broccoli. The top of the crown is less than an inch from the waterline it receives 170 PAR. That is the end of the happy part of the story. underneath the crown - ( where the broccoli stalk would end and the crown begins ) is below six inches of water. If i put the sensor there; up against the "stalk" I get 16 PAR. It gets worse from there. Where the "stalk" enters the substrate the available light has been reduced to 1.2 - 1.5 PAR. Still keeping the sensor on the substrate yet moving it less than four inches from that point the reading returns to the afore mentioned 51 PAR. Regard that these readings were illuminated by a single source. Strange thing about shadows is they dimish as the distance increases between source and subject increases. Perhaps one could push more light down below by simply distrubuting the same intensity over a larger source. Like 2- 13W bulbs rather than 1- 23Watt bulb This is where flouresents shine. Weak intensity - large distrubution Quote Link to comment Share on other sites More sharing options...
jvision Posted June 10, 2011 Report Share Posted June 10, 2011 The reason shadows deminish further away from source is that the light bounces off different things in the tank. The intensity is probably pretty week, but it'll drown out the shadows. Quote Link to comment Share on other sites More sharing options...
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