# PAR vs PUR - Latest Opinions in Planted Tanks



## JohnC (28 Nov 2012)

Hi,

I'm in a discussion with a well know budget bulb supplier (i won't mention the name out of politeness) about some T5's i got the other day. They were noticeably dimmer to the naked eye so I decided to get my PAR meter out and do a little testing....

They are coming out 15% less PAR then my year old Arcadia Juwel type plant bulbs. 

Since I was already thinking my Glosso is on the verge of wanting a bit more light in places and putting the reflectors on, the new bulbs were meant to keep it in the "happy range". Now i'm thinking the opposite. Light reduction and will need the reflectors. 

So being slightly miffed I sent a polite email to said supplier and his reply with this -



> "Hi John,
> 
> Thanks for your email. I’m sure you already know that the PAR of a tube isn’t necessarily the most important measurement to take, here at ******* when we develop a tube we look much further than PAR. A high PAR reading doesn’t necessarily mean a better bulb, we try to use PUR (Photosynthetic usable radiation) as our base line as  this is the part of PAR that is usable by plants and corals for photosynthesis. If I can give you the example of a standard household fluorescent, it has an incredibly high PAR reading as it is designed to be “bright” to the human eye, out of that PAR there is very little PUR.
> 
> ...



Now obviously there is a mix of cut and paste stuff in there and fuzzy definitions of stuff as well as slipping into Lux chat in the second paragraph.

But this PUR thing got me researching before answering back. (the bulbs are cheap and even show a 10% difference in output between them).

The planted tank forum has some good discussions between Tom and others.... The gist of which is that there hasn't really been any/much work done into different PUR needed for the 300 - 400 species of aquatic plant. Where in the Marine world there has been work done on this front. 

http://www.plantedtank.net/forums/showthread.php?t=78632

http://www.plantedtank.net/forums/showthread.php?t=136341

So my question is -

I'm aware PUR is being pushed by the LED manufacturers and marine world but is it just "fuzzy science" currently?

Has there been enough new research into PUR in tropical plants since Tom Barr made these posts for a cheap bulb seller to feed me these lines? or am I just being fobbed off with some science chat like I feel i'm being?

Oddly I do have the perfect test to see since my glosso was on the edge of not enough light in my opinion. If it grows up now I will know.

Opinions specifically on new information not covered in the planted tank thread please. The discussion there is already quite in depth (thanks to Tom and the  other contributors a few years ago).

Best Regards,
John


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## Ian Holdich (28 Nov 2012)

That is very interesting John, thanks for posting.


Ps ime, glosso doesn't need a lot of light, it needs plenty of flow and decent amounts of c02. Upping the light will only lead to more probs.


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## JohnC (28 Nov 2012)

Ian Holdich said:
			
		

> That is very interesting John, thanks for posting.
> 
> 
> Ps ime, glosso doesn't need a lot of light, it needs plenty of flow and decent amounts of c02. Upping the light will only lead to more probs.




Oh indeed. It was sitting happily on bout 45 PAR to 35 PAR in places.... now 35 to lower which I think will be creeping into too low..... I took the reflectors off about 6 months ago as I was over 55 PAR and it was not needed.


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## hinch (28 Nov 2012)

from my basic understanding its all bullshit.

since light is a particle stream (photons) by increasing the brightness you increase either the quantity of photons or the energy value carried by the photons.  increasing either value would lead to an increase in usable radiation. the actual used amount though is dependant not on the bulb but the target of the radiation and how efficiently it can convert the incoming light to energy to be used and what kind of surface area it has available for ps.

rule of thumb brighter = more energy available.   this leads to an increased demand for ferts and co2 to allow the plant to use the amount of light its being bombarded with as the plant will always want to use all the light its receiving. too much light and not enough co2 or ferts leads to problems as we all know and its finding the balance between incoming energy vs raw building materials so you don't end up with an excess of either.

hope that makes sense it does in my head (someone correct me if i'm wrong though as this is just very basic comprehension of the physics)


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## JohnC (28 Nov 2012)

hinch said:
			
		

> from my basic understanding its all bullshit.
> 
> since light is a particle stream (photons) by increasing the brightness you increase either the quantity of photons or the energy value carried by the photons.  increasing either value would lead to an increase in usable radiation. the actual used amount though is dependant not on the bulb but the target of the radiation and how efficiently it can convert the incoming light to energy to be used and what kind of surface area it has available for ps.
> 
> ...






the gist of the explanations of PAR vs PUR have actually been done very well by Tom et al in this thread....

http://www.plantedtank.net/forums/showt ... hp?t=78632

it's not that i'm asking about specifically now. it's more an enquiry that since these threads were over a few years old if research into PUR response in aquatic plants has come on enough that PUR output can be used by bulb manufacturers as anything more then "the science bit" in trying to justify why their bulbs "seem" weaker using available standard, universally adopted, measuring devices like a PAR meter (and in this case my own eye). 

Best Regards,
John


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## hinch (28 Nov 2012)

well thats the point if they are weaker then they are weaker end of story his explaination of developing "useful" bulbs vs "total radiation" is bullshit.


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## Ian Holdich (28 Nov 2012)

Just for clarification Hinch, you mean brightness in watts, not just brighter to look at?


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## hinch (28 Nov 2012)

well the wattage is just the amount of energy given (or could be measured in amount used ie 24w bulb gives out 18w usable etc but  thats kinda pointless again as increase in wattage would still result in a brighter output)

The brightness when looked at by us depends on colour ranges a dark blue/purple bulb may not seem very "bright" but it may still give off a large amount of energy via radiation (uv good example here) which is usable by the plant however a bright white in a lower wattage may appear brighter but give off less overall energy.  This is where the PAR/LUX/whatever measurements come in they're supposed to be fixed numercial equivilance of the available energy.  I say supposed as they're always skewed to whatever the manufacturer wants you to believe or they invent stupid new "standards" such as PUR.


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## Ian Holdich (28 Nov 2012)

I was just clarifying your post as you say if it 'look's' brighter it is brighter, which isn't true, however you clarified it so it doesn't really matter lol!


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## hinch (28 Nov 2012)

i was assuming a standard "white" bulb not considering different spectra bulbs actually forgot completely how that can effect our perception of brightness


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## hinch (28 Nov 2012)

just actually read tom's thread linked earlier and it basically says exactly the same as me just more technically/better worded  glad to know I was in the right general area. he says PUR is a useless measurement too \o/


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## Ian Holdich (28 Nov 2012)

That's the thing, people will often say they notice a drop in brightness with there own eyes...again this isn't humanly possible when it comes to energy emitted from the bulb. I wish it was possible as it would save a lot of these discussions to whether lumens and k ratings make plants grow better.


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## Tim Harrison (28 Nov 2012)

It sounds like the usual hokum that seems to wend its way in to aquarium folklore via the plain stupid, ignorant, and vested interests.

I think the shopkeeper is trying to blind you with pseudoscience in an attempt to fob you off with substandard wares. PUR isn't easy to quantify, even under laboratory conditions, for all the reasons already mentioned. Therefore, the shopkeepers comment is subjective and meaningless.

But equally, considering PUR is a factor of PAR, it's fairly safe to assume that a drop in PAR equals a drop in PUR, especially if the bulbs in question are full spectrum. Further, in broad terms since PAR corresponds more or less with the range of light visible to the human eye a perceived decrease in light intensity could conceivably equate to an actual decrease in PUR. 

But at the end of the day all this is academic. The bottom line is if you are not happy with the product you are perfectly within your rights to send it back for a refund, particularly under distance selling regulations.


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## plantbrain (28 Nov 2012)

Ian Holdich said:
			
		

> That is very interesting John, thanks for posting.
> 
> 
> Ps ime, glosso doesn't need a lot of light, it needs plenty of flow and decent amounts of c02. Upping the light will only lead to more probs.



I have seen some very nice Gloss with very low old school T8 bulbs from the 1990's.
Very low tech stuff with DIY CO2.

T5's:
This is my more recent Nature style approach using 1.2 W/gal at well over 1 meter away from the plants.
I do have the option of using 2x as much light, 2.4 w/gal, but it is much more difficult to manage:











There is an old fall back that Light makers and others who simply do NOT know.....but like to speculate......that PUR plays some important role. They sell you the bulb, make the claim, but do not bother to do the research with radiospectrometer to verify whether or not this actually influences plant growth rates, color, aesthetics etc. 
It is *a lot more work to do that *versus say just doing some PAR measurements and curves. 

Now we use PAR mostly because it's a good trade off for the work to use the meter, labor and comparative value vs PUR. PUR is more informative but the trade off has a steep cost and labor price. The skill needed to do the research also is greater and needs more controls. Aquatic plants are highly adaptable, corals, not so much.

To the lighting makers, you cannot use this argument and then also not provide research to support in aquariums.
You can speculate, but that needs to be clear. I buy that the work has been done, mostly by Reef aquarist in that hobby, but the plant hobby is NOT likely going to do that for you. You cannot have your cake and eat it too.

There is some observations that would lend itself to some differences in PUR vs PAR m my own experiences, as most other issues were ruled out, but this is indirect evidence. To test it, would require a lot of work for virtually no gain for myself.

It is less work to swap and switch bulbs till I get a nice result. I'm not trying to squeeze every last possible bit of PUR out of my lighting system and I'd bet most planted hobbyists are not either.
This manure has gone on for the last 20-30 years in the hobby.

PAR meters have been able to make wide ranging comparative sampling from a wide range of plants and hobbyist trying to duplicate various lighting set ups. This has been very informative, but as you get farther into it, law of parsimony or Occam's razor starts to apply......and with hobbyists, they have all sorts of other factors making determination and utility of PUR much harder to realize. 

Fear not, many Biologist that study aquatic plants only use PAR, not PUR. I've found virtually nothing on the matter in about a decade of looking. That said, most Biologist study plants under natural sun light, not fake light. So we know the source better.


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## plantbrain (28 Nov 2012)

hinch said:
			
		

> just actually read tom's thread linked earlier and it basically says exactly the same as me just more technically/better worded  glad to know I was in the right general area. he says PUR is a useless measurement too \o/



Well, not useless, but rather tough and impractical for aquarist.


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## plantbrain (28 Nov 2012)

JohnC said:
			
		

> hinch said:
> 
> 
> 
> ...



No and no.

Mark Twain said it well:

"Advertising is the art of getting people to buy stuff they do not want, with money they do not have for something they do not need. Get your facts first, and then you can distort them as much as you please."


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## Ian Holdich (28 Nov 2012)

My iaplc entery was grown under 2 18w T8's. the glosso did well.




Ian IAPLC 2 by Ian Holdich, on Flickr[/quote]


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## JohnC (28 Nov 2012)

plantbrain said:
			
		

> JohnC said:
> 
> 
> 
> ...



Just what I thought. 

I'm almost more peeved that they tried to fob me off with the email they did. Half of the paragraphs don't even make that much sense. 

The tank actually looks dull too. When I've sorted my work for the day I'm going to ask for my money back.

Thanks for the replies everyone, I won't name the bulb supplier on a public forum as i don't want to get UKAPS into any trouble but if anyone wants to know my opinion/experience they can pm me.

Best regards,
John


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## JohnC (28 Nov 2012)

Ian Holdich said:
			
		

> My iaplc entery was grown under 2 18w T8's. the glosso did well.
> 
> 
> 
> ...


[/quote]

That is just lovely.

I'll adjust the outputs of the spray bars to give the glosso more flow accordingly.


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## plantbrain (28 Nov 2012)

Ian Holdich said:
			
		

> My iaplc entery was grown under 2 18w T8's. the glosso did well.
> 
> 
> 
> ...


[/quote]

The E. vesuvius and the Gloss make excellent contrast at that scale.


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## plantbrain (28 Nov 2012)

John, I think you might be better served and have a bit more positive spin if you simply try a few different color mixes and see what you like the best. I've held this view for maybe a decade or more.

I just keep trying different bulb types and combos till I happen on something that is most appealing to the eye. You can get an idea on line and over the net by looking at pics and asking folks also, then narrow the choices down.

If you see freaky magenta red colored plants= photo shop got away from them........so be careful.
I like many bulb fixtures so I can mix and match many different combos.

Given most will try a few different bulbs this way, it would seem better for the bulb makers/resellers to use this approach based on aesthetics and trial and error for each aquarist, than BS-ing the consumer. There's no easy answer to what is best for you, me or anyone else due to aesthetics and various goals and personal opinion. 

You need to define what it is you like best.


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## JohnC (29 Nov 2012)

plantbrain said:
			
		

> John, I think you might be better served and have a bit more positive spin if you simply try a few different color mixes and see what you like the best. I've held this view for maybe a decade or more.
> 
> I just keep trying different bulb types and combos till I happen on something that is most appealing to the eye. You can get an idea on line and over the net by looking at pics and asking folks also, then narrow the choices down.
> 
> ...



Partly that is the problem. I actually like the colour they put out. It's very natural. They just are not as powerful, both on the PAR meter and through the naked eye. 

They look dim.

I see what you are saying thou. I can easily work with them, I just object to being fed BS when all they really needed to say was something along the lines of "you get what you pay for" and i'd have excepted it.

If I pop the reflectors on I imagine i'll come back up to 50 PAR that I tend to aim for and the whole tank will look brigher. I was just avoiding that as it makes maintenance a little bit more tricky.


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