chimera Posted July 26, 2006 Report Share Posted July 26, 2006 All the discussion on lighting lately has intrigued me, so much so that i bought a lux meter. A lux meter measures the illumination of light (where 1 lux = 1 lumen/square metre and 1 lumen = the amount of light intensity eminated from 1 candle at 1 foot away or 0.093 foot-candles). As a rough indication, the amount of lux on the surface of seawater on a typical reef at noon is about 110,000 - 120,000 lux. While the preferred method to evaluate the intensity of light entering the aquarium is PAR (photosynthetically available radiation) or PPFD (Photosynthetic Photon Flux Density), PAR meters are exceptionally expensive ($1,000+ supposedly) (PAR/PPFD units are measured as μmol/sec/m2). Supposedly these do a better job of accounting for colour temperature in their measurements as well. You cannot "algebraically" convert from lux to PAR or visa versa, as there are different variables involved such as the light source and kelvin rating. However there have been studies done in the past (by Dana Riddle) where he produced a table showing conversion factors based on different bulbs. This is what I intend to use to get approximate PAR ratings (I say "approximate" as the studies only provided conversion factors for radium and iwasaki bulbs from what i could see, I run narvas) The first thing I have to do is dismantle and water-proof the lux meter sensor. The next thing I plan on doing is taking lux readings from different depths in the tank (fingers crossed it doesnt leak ) The initial test I did was quite interesting. I took a comparison between two of the 400W narva bulbs I have (both were brand new and added at the same time, the third was added a month later). I have always thought the centre bulb was somewhat dimmer than the right hand bulb, but had always attributed this to the centre glass brace being the cause. My gut instincts proved me right, the bulb intensity is different. The reflectors as most of you know are lumen arcs. Here are some readings I took at the water surface. The bulb is 7" away from the water surface, the bottom edge of the reflector is 5" away: Centre bulb: centre of reflector: 140,000 lux corners of reflector: 30,000 lux centre of edges of reflector: 25,000 - 45,000 lux Right bulb: centre of reflector: 170,000 lux corners of reflector: 40,000 lux centre of edges of reflector: 30,000 - 50,000 lux The difference in lux at the centre/edges of the reflector were higher where the edge followed the length of the bulb and lower where it was the ends of the bulb. I am going to raise the whole hood up 3" and see how much difference it makes. According to this study (which I posted on fnzas a while ago) http://www.advancedaquarist.com/issues/ ... eature.htm it shows that 9" and even 12" from the water surface with lumen arc reflectors still provides good coverage without losing a great deal of intensity. Especially considering the lux at the centre of mine is 50,000 more than sunlight on a typical reef! From there, bulb selection is key on getting the right amount of useable (colour) light to the corals. Quote Link to comment Share on other sites More sharing options...
chimera Posted July 26, 2006 Author Report Share Posted July 26, 2006 Very interesting - I just lifted my lights up by 3". Other than it looking one hell of alot better (before it was aesthetically "too" bright) the lux are alot more even across the water surface, just as the study in the link above suggests. The bulbs are now approx 10" from the water surface, bottom edge of the reflectors at 8" away. The centre of the left and right bulbs is now 100,000 lux, centre of the centre bulb is 80,000 lux (again, probably a slightly more crap bulb from factory) Interestingly lux at the corners and edges of the reflectors have not varied much at all presumably because light emitted from the bulb/reflector next to the one I'm measuring is helping "add" to it. Much happier with the lighting on the tank now however it will be interesting to see how the corals respond (better, worse or the same?) Worth the $50 for the lux meter I think as I'm sure I'll continue to use it. Will post up some results once I get around to waterproofing it. Quote Link to comment Share on other sites More sharing options...
JoeBlog Posted July 26, 2006 Report Share Posted July 26, 2006 Awesome Chimera! A buddy and I were talking about doing the same thing, but MD doesn't carry their submersible Lux meter for another 6 months. Looking forward to seeing your readings under water. Cheers, Steve Quote Link to comment Share on other sites More sharing options...
Ira Posted July 26, 2006 Report Share Posted July 26, 2006 I'd just throw the meter into a sandwich bag and drop it into the tank. Quicker and easier than disassembling it and somehow waterproofing it. Quote Link to comment Share on other sites More sharing options...
chimera Posted July 26, 2006 Author Report Share Posted July 26, 2006 that would be difficult considering the sensor and lcd unit are separate! easier to waterproof i think Quote Link to comment Share on other sites More sharing options...
JDM Posted July 26, 2006 Report Share Posted July 26, 2006 very interesting, where did you get the lux meter? Quote Link to comment Share on other sites More sharing options...
chimera Posted July 26, 2006 Author Report Share Posted July 26, 2006 trademe. lux meter only has good accuracy at low range (0-50,000) seems to be able to do up to 200,000 but accuracy is not as good. so take the figures above with a grain of salt (i rounded them up/down to the nearest thousand anyway) i just wanted to get an approximate reading so i could see how high i should be putting the lights plus see how much there intensity drops over time (relative to when they are new of course) Quote Link to comment Share on other sites More sharing options...
WEKA Posted July 26, 2006 Report Share Posted July 26, 2006 Put the sensor in one of those screw top jam jars with a cable gland mounted thru the lid for the LCD assuming it has a round cable Quote Link to comment Share on other sites More sharing options...
TM Posted July 26, 2006 Report Share Posted July 26, 2006 very interesting. By the way does anyone have the link to Sanjays page that has all diff types of bulbs listed and there par rating? i have the main page but can't seem to find the one with all the par ratings http://www.reeflightinginfo.arvixe.com/ This is also good for articles about ballasts, bulbs and reflectors. http://www.personal.psu.edu/faculty/s/b ... arium.html Quote Link to comment Share on other sites More sharing options...
puttputt Posted July 26, 2006 Report Share Posted July 26, 2006 and you thought I was mad having my lights so high haha Quote Link to comment Share on other sites More sharing options...
chimera Posted July 26, 2006 Author Report Share Posted July 26, 2006 and you always double click when you hit submit Quote Link to comment Share on other sites More sharing options...
puttputt Posted July 26, 2006 Report Share Posted July 26, 2006 not always Quote Link to comment Share on other sites More sharing options...
cracker Posted July 26, 2006 Report Share Posted July 26, 2006 I put my one 250mm above water level to start and its still bloody intense! Quote Link to comment Share on other sites More sharing options...
jetskisteve Posted July 26, 2006 Report Share Posted July 26, 2006 http://www.advancedaquarist.com/issues/ ... eature.htm Quote Link to comment Share on other sites More sharing options...
chimera Posted July 26, 2006 Author Report Share Posted July 26, 2006 gee steve, that looks exceptionally similar to the link I posted at the top of this page Quote Link to comment Share on other sites More sharing options...
puttputt Posted July 26, 2006 Report Share Posted July 26, 2006 Quote Link to comment Share on other sites More sharing options...
jetskisteve Posted July 26, 2006 Report Share Posted July 26, 2006 doh :oops: Quote Link to comment Share on other sites More sharing options...
trinity Posted July 27, 2006 Report Share Posted July 27, 2006 :lol: :lol: :lol: Quote Link to comment Share on other sites More sharing options...
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