# PAR and other stuff - just for myself ;-)



## jesperl.dk (16 Feb 2017)

Do I have enough light? – surely a common question. My own experience is that in my aquarium I have barely, what you would call “high light”. I can grow a glosso carpet without too much trouble, but specially in the corners it grows slower and will not stay low.
My aquarium is length: 100 cm; width: 40 cm; height: 50 cm. That gives 200 L.
I have two fixtures with each two 39W T5HO, and in each I have a 840 and a 865 tube, all together 156W with good reflectors.

In older times, it was common to calculate watt per litre and use that as a guideline, for example:






I have 0,76 W/l, which puts it below “High lighting” per the table above. The values in the table are pretty common ones, but such W/l recommendation tends to be conservative with their expectation of the efficiency of the tubes and of the reflectors, so I think I am good with my experience that I have “high light”, but just barely. That is of course not so surprising, as I used such a table when deciding what fixtures to by 5 years ago 

Lately there have been a move towards using lumen per liters instead of W/l, largely driven by Tropica, http://tropica.com/en/guide/make-your-aquarium-a-success/light/ . This takes away the question of the efficiency of the fixture, but leaves the question of the efficiency the reflectors open. Tropica has this guideline:





My tubes are each 1750 lumen, in total 7000 lumen, so I have 35 lum/l. Almost, but not quite advanced 

For some years the discussion has been going that the best way to judge your light is to measure the PAR for your specific fixture, in the water, right at the substrate, which often are higher at the back than at the front. This handles the efficiency of both the fixture and the reflector, the quality of the light, the depth of your aquarium, and the position of the fixture. See for example http://www.plantedtank.net/forums/10-lighting/184368-lighting-aquarium-par-instead-watts.html, which is a commonly referenced article.

But how do you measure PAR? – few of us have a proper PAR-meter. And perhaps even more interesting, what is the PAR-equivalent of the tables above? What PAR should you have to have “high light”, so you can grow “advanced” plants? I have not been able to find a table that seems to be widely accepted – please let me know if you know of one. I have seen postings saying things like: PAR value between 10-30 as "low light," 30-80 as "medium light," and 80-120 as "high" light." But it is not clear what the source is – I mean, a source that has done actual experiments and measures.

Well, I had a Seneye in the drawer. 4 years old and never used. The Seneye is hopeless in almost any way. It should however be able to measure PAR as well as several other lighting parameters. There have been a few tests of the Seneye, comparing it to a proper PAR-meter, and it looks like it can give an indication of the actual PAR, but it is not precise and it is very sensitive to be held in the right direction. Time to measure PAR with my Seneye.

My aquarium has been set up for 15 days, so it has some plants, but they are not yet that big. I took measures at the top of the plants (instead of at the substrate). Remember my aquarium is 50 cm high, and the tubes are about 8 cm above the aquarium. I measured at the following positions and at the indicated heights above the bottom of the aquarium.





This gave the following PAR values. The colors are just chosen by me to differentiate the values. The light gray numbers are not actual measurements, but are just the values from the left side mirrored to the right side.





Interesting! Very large variation in the values, but it makes sense. My tubes are obvious too short for the aquarium, no wonder the glosso struggles a bit in the front corners. On the other hand the 4 tubes are spread nicely over the width of the aquarium.
Are my values medium or high? According to Seneye, you should have something like 150-200 to grow demanding plants, see http://answers.seneye.com/index.php?title=en/Aquarium_help/What_is_PAR_&_PUR_?/fresh_water_plant_PAR_levels . That seems reasonable compared to my own admittedly very limited experience. But it is very different from most other recommendation you can find at different planted aquarium sites. I might of course just be because the Senye measurements are off, but I am not sure they are so much off.

Recently I bought a set of IKEA hydroponics indoor garden sets. If you do not know them, you should check them out the next time you are in IKEA, they are easy and fun!





They are of course also a bit like aquariums. Well, at least a bit like palladiums  While I was at it, I did some PAR readings on them as well. There are 40 cm from the substrate to the lamp, and I did measurements approximately 3 cm and 12 cm above the substrate.



 



The values are not that far off from what I have in the aquarium. These lamps (which can be bought separately), can obviously be used as an aquarium fixture. On the other hand, you will have to use more than one to get enough illumination in the corners. These readings are in line with how my plants are growing in the IKEA sets, and this insight will course me to shift the plants around in the sets now and then.

The purpose of this exercise done for myself, was to get some kind of baseline before I have a go at building my own LED fixture sometime in the future. I hope you enjoyed it a bit as well


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