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The Corroboree

PAR meters- a question for the geeks

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Are there any electronics geeks who can tell me why the f*k PAR meters are so expensive?  The standard models don't even have a logging function FFS, and start at around AUD $300


PAR ( Photosynthetically Active Radiation ) meters measure light based on that part of the spectrum which is used for photosynthesis by plants.




Dead handy little buggers those meters. Our human irises open and close to adjust the amount of light they let in, but plants don't have this light-adjusting capacity the same way. So a plant can be getting much less useful light than we realise til we test it.


Plants in tissue culture photosynthesise way less than outdoor plants because they use the sugars ( or other carbon sources ) in the media for energy. It's why we get away with using fluro tubes and get good growth. But fluro tubes lose a large proportion of their photosynthetically useful light after 3 months and need replacing- the light at those wavelengths isn't differentiated by our eyeballs, but the plants notice, believe me.


I've been told that other indoor lights- metal halides for example- also lose some of their PAR strength after a period of time, but I have no experience with this.


And I've seen people swear blind their plants are sick, when after careful checking their plants aren't getting enough light because they're shaded for the parts of the day when there's no-one around. This is more pronounced in winter when the days are shorter and the sun's angle of attack is different


I bought plans to make a unit with an Arduino using LEDs, but it's a world of hurt for me and the tek ( to my n00b eye ) seems to be primitive and possibly inaccurate. It'll have to wait until I have some geek mates in-house for a weekend with soldering irons and whisky and those weekends never turn out the way they're planned anyhow :D


Fuck it, I want a network of the little buggers with temp and PH, two sensors it's easy to build loggers with. Then I can really see what my plants are up to. Plus it could save me some $$ replacing fluros all year. And maybe save some planty lives if there are dodgy tubes in the rack


Anyone know of a cheap chip that's up to the job?

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Bugger, forgotten how to delete topics


Seems there is a bunch more DIY stuff out there than there was last time I checked, despite the commercial units being the same price


I need to do more reading on the DIY stuff and try to evaluate how good the latest teks are for PAR

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HI Darklight, 


  I'm a wanna be Geek.  I have done a fair bit of work with arduino and can understand how the programming and hardware works with a bit of time.   I could take a look at the plans for you if you like?   I'm interested in the PAR  of lights too.  I can't bare throwing things away when they still work    HPS lights etc but I know my plants suffer for it.   I also have an interest in LEDs for use in aquatic plants  which makes knowing PAR important. ( probably not that important  really ;) ) 

  I kind of started a grow room monitor with multiple temps, humidity, Ph, EC etc.  I looked into good light sensors that give useful spectrum readings but there didn't seem to be many available.   there was one system I saw which used astronomical light filters to block specific wave lengths --  it kind of seemed like a clunky work around. 


 we should have a chat and see if there is anything we can do.  for mutual benefit!


 cheers Jim

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How do the commercial units do it ?

Do they split the light with a grate and then use individual photodiodes for each desired wavelength ?

I'd imagine there will be some tricky maths involved to deal with the calculations. Light intensity starts getting very complicated when you vary the sensors from the light source, so maybe it will need an inbuilt lux meter to give a baseline intensity and then maybe lookup tables to compensate for varying distances in test samples. Different tubes emit different frequencies too so even though the final solution could be quite simple establishing a baseline and referencing it might be a bit tricky at first.

Could be talking out of my arse too, I haven't arduino'd anything for quite some time.

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