Aquarium Plants - Barr Report - Articles http://www.barrreport.com/ Articles, Public Archives, and DIY Projects en Wed, 19 Jun 2013 14:32:48 GMT vBulletin 60 http://www.barrreport.com/images/misc/rss.png Aquarium Plants - Barr Report - Articles http://www.barrreport.com/ Converting a Lux Meter to a PAR Meter http://www.barrreport.com/showthread.php/12536-Converting-a-Lux-Meter-to-a-PAR-Meter?goto=newpost Tue, 11 Jun 2013 03:14:30 GMT About a year ago I discovered that we can buy a lux meter, made in China, for about $13-$25 on Ebay and Amazon. This aroused my interest in trying... About a year ago I discovered that we can buy a lux meter, made in China, for about $13-$25 on Ebay and Amazon. This aroused my interest in trying to find a way to convert one into a PAR meter, and at that price experimenting isn't very costly. So, I bought a few of them and started a long, long project! The model number of the lux meter I used is LX1010B, which seems to be available from more than one Chinese manufacturer

Initially I took the easy way out, and simply put the sensor, which is separate from the readout meter, in a waterproof housing. This gave me a lux meter that would work under water, but holding it down against the buoyancy proved to be more than I wanted to work with. Next, I cut up the sensor, and put just the minimum part of it in a water proof housing. It was still too buoyant, but this also let me experiment with filtering the light to try to approximate the PAR spectral range. Unfortunately, the photodiode sensor in these has a built in, one piece filter that eliminates the IR and UV portion of the spectra, and adjusts the visible spectral sensitivity so it reads little more than the green light.

I then found that we can get a free sample book of Roscolux gel filters from any retail dealer for those filters, and there was a local dealer near me. I picked up a book of samples, each of which is shown in their website, http://www.rosco.com/filters/roscolux.cfm with a graph of the spectral response for that filter, plus a tabulation of the response for every 20 nm portion of the spectrum. This enabled me to spend many hours with a spreadsheet trying to find a filter or combination of filters that would magically transform the lux sensor to a PAR sensor. (It can't be done!)

Fortunately, a poster on The Planted Tank was working on building a PAR meter from scratch, and he found a readily available photodiode that has a much better spectral response. So, I chopped off the sensor from my lux meter and started designing a sensor from scratch, using Roscolux filters. This is the last version, which has worked very well:

ImprovedPARSensor_zpsf553d120.jpg

To be continued:
Attached Images
]]> Articles VaughnH http://www.barrreport.com/showthread.php/12536-Converting-a-Lux-Meter-to-a-PAR-Meter