Initial PAR results

[Gerryd]

Hi all,

I just received my Apogee quantum meter with remote sensor and took a few quick measurements for fun, while I work out a measurement grid

I also purchased the leveling platform. It has a little level glass viewer as well as three adjusting pins.

Quick and easy to use and very responsive to small sensor placement changes.

Using 2 30 watt Verilux brand regular flourescents mounted 7.5" above the surface on a 45 gallon 24" tall tank:

1. Just at the surface with the sensor ABOVE the water: 50
2. Just at the surface with the sensor BELOW the water: 40
3. Placed on the substrate: 20

Going to the 3x150 MH 6500k setup also at 24" depth of tank:

I just placed the sensor in two places while I adjusted the lights. Top and bottom directly in line with each other.

17"

1. Sensor above surface: 215
2. Sensor below surface: 175
3. Sensor on substrate: 55

14"

1. Sensor above surface: 250
2. Sensor below surface: 215
3. Sensor on substrate: 65

11.5"

1. Sensor above surface: 345
2. Sensor below surface: 300
3. Sensor on substrate: 75

It is amazing how the PAR rate changes even moving the sensor a little bit. I know MH have a bad spread, but it is really ridiculous when you see it.

Plus, the amount of reduction between under and over the water line is dramatic.

In some of the plants beds at the substrate, I was reading only 10-15 even though the growth looked good, no algae, and some pearling down there.

Of course, these are just first quick impressions, that I wanted to share.....

Just very interesting stuff. Nice to have a few facts for once.

P.S. all the above is null and void due to possible operator error lol

P.P.S. If anyone is in the WPB, FL area and wants to use it, PM me and see if we can meet to say hi and take a few measurements. It is quick and easy.

 

[VaughnH]

Gerry, I just spent 15 minutes doing rough plots of your data, before finishing reading your post. At least your possible operator error would explain why I found your results "interesting". Do you have the hemi-spherical sensor that integrates light coming from all directions? I know with Tom's flat sensor all you had to do was breathe wrong and the reading could drop or rise substantially. I found trying to hold it under water and keep the sensor face parallel to the water surface was impossible for me. Your leveling platform might solve that problem.

 

[Gerryd]

Vaughn,

Hope you didn't waste too much time....

I looked here at the specs and there is no mention of if it is a ' hemi-spherical sensor ' or not. The sensor looks like a small molehill shape if that makes any sense with the sensor on top. The level view glass is built into the platform.

It is as stated, very sensitive to ANY movement. The platform though at least kept it steady in my two measurements, as the gravel supported it nicely in one case, and I rested it on one of the cross frames for the other. Both times, the level viewer showed 'on target'. Even when I placed it just under the surface, I was able to hold it steady enough to get a constant reading.

The platform is heavy steel(?) and very useful and I also was able to balance it on wood or stones at various levels in the tank to get readings. No wonder plants grow better the closer they get to the surface lol

As an example, placing the sensor on one of the two cross bars at each end and center gave the following numbers going center-back-front:

Bar 1: 336-91-106 at 17.5"
Bar 1: 396-116-71 at 14.5" I think this last number is LESS because the spread is less with the light closer to the water.

My lights are somewhat off center as I had to use the studs for the weight and the tank would have entered the hallway if I had centered it, oh well. So the bar may get a bit of two lights as opposed to mostly 1, if that makes sense.

I can slide the lights back and forward as well, as a slight slant from left to right and back to front as they simply rest of closet hardware......so they are very mobile at each height adjustment.

Quantum Meters: Apogee Instruments: SPECTRAL RESPONSE

Not sure how much operator error there can be, as the unit consists of the sensor and an on/off switch, which I was able to figure out

I just wanted to put this out, because if these numbers made no sense, I would know right off..I was able to keep my hand steady (???) to get a decent reading.

What did you find 'interesting' about them, BTW??????

Just for fun, moving the sensor slowly, changed the measurements rapidly with it, but I am unsure if this is a proper use of the device., in that it needs to be stable and unmoving for a correct measurement to occur. I would expect that to be the case.

More seriously, I was thinking of the following basic pattern:

I have 3 lights with lenses rectangular in shape.

I would take 5 horizontal measurements for each light at each corner and the middle of the lens. 5 x 3 = 15 readings.
I would then take 3 vertical measurements, at just under the surface, mid-water (12"), and substrate (23"), as close to the 5 horizontal points as possible. 3 x 15 = 45 readings.
I would then take 6 vertical measurements, 3 at each end, corner, middle, and corner. 6 x 3 = 18 readings.

Plus a few tossed in under plants, in thickets, under wood, etc, and I think I would have a decent matrix to map the low to high light areas.

Thoughts?

I am probably like a mad scientist misusing a perfectly benign device to take over the world.....

 

[VaughnH]

Your sensor sounds like it is an integrating spherical sensor, that accepts light from all directions above it. What I found interesting was the following:
The drop off in intensity in air, with distance doesn't look much like either an inverse square or direct relationship.
The drop in intensity right under the water surface seems to drop too much, since water barely absorbs light, and very little light should be reflected off the water surface.
The drop off in intensity in the water and the drop in air are parallel curves, roughly, but as if there is a fixed loss from passing through the surface of the water.

I will probably play with the data a little more, and see if it makes more sense to me tomorrow. I'm probably just missing something in looking at this. It really is interesting, without the quotation marks.

More data is always more interesting, by the way. When I was working, we had a saying, "no engineer ever had too much data!"

 

[VaughnH]

I graphed your data much more accurately, using log log graph paper. This looks like:

Not knowing how far the MH bulb is recessed into the fixture I assumed that to be 4 inches, because it makes the data fit better. Then I assumed that your readings just above the water surface were more accurate that just below the surface, for the same reason. With all of that it appears thay your MH light drops in intensity by the inverse square rule, or close to it. If you lowered the sensor only 2 inches to get it into the water, the data fits an inverse square relationship very well.

Good data!

 

[Tom Barr]

Gerry, you might consider the practical matter here, what effects the plants have as they grow towards the plants.

How might this influence growth through time and space?

What are the min PAR readings at the edges of where you want certain plants?
What are the max values?
Move the sensor around, rotate it 3D, move from leaf to leaf.

Inside the plant beds vs at the top, does wood, rock reflect the light? Other plants?

What is a good range for plants? which plants?

and so on...........
Inverse square law alone is only part, the good thing about havign a light meter is now you can compare on equal terms the light that someone else is using.

Also, think in terms of a range, an ellipse of scatter vs a line.
Plants are biological system and will never have those perfect correlation lines with many data points. the living world is not black and white, unless you are a Zebra(Black with white stripes, or white with black stripes?).

Regards,
Tom Barr

 

[Gerryd]

Tom,

Yes, the practical is more of what I am after.

My whole intention is too look at the things you suggest, and make better scaping/planting choice decision, based on that type of data.

I was just intitally surprised at the amount the light decreased with just small increases in distance..........

I was guessing and experimenting before... If a plant did not do well, in a location, I would try moving it to another and see how it did there.

While I am doing so, I will record as much as possible. That should give Vaughn some better data, if he would be kind enough to plot it again.......

Vaugh,

I would say the bulbs are recessed about 1-1.25" in the fixture if you measure from the inside of the lens. No way 4". I will measure accurately later..........

I just adjusted the lights so the bottom of each lens is exactly 9" above the water surface.

Will take some new measurements at that height.

I intent to use this height for all the other readings that I will do.

I think I will use several pieces of PVC anchored in the substrate at various lengths, to place the sensor on. Then I can have it steady, and be more assured that my 5 point pattern is at least at the same height for each bulb.

I think then that the same set of readings at 1 and 2 week intervals would be interesting. I will do no pruning in that time.

Thanks for all the info and advice.

Will post all results (and of course questions).

 

[VaughnH]

I always find that my data proves my theories a lot better when I have the flexibility to to alter the data points as I wish. You surely aren't suggesting that I plot only real data, are you?

Well, if that's the rules I will abide by them. Bring on the data!!

 

[Gerryd]

Hi Vaughn,

I would never accuse you of such a thing!

In the software development world, they call that 'hard-coding' a variable lol

So, I took some quick readings of the substrate, as I want to grow some HC or glosso, and a few of the surface for a quick compare.

Lights are exactly 9" above the surface on a 24" tall tank.

Substrate readings:

Range: 10-110 based on where it was. Highest readings were directly under the bulbs, and the lowers were in the shade of plants and wood and at the very ends and corners of the tank.

Open areas where I want a ground cover range from 55-100. This is just dragging the sensor around with me. Was kinda fun and easy.

Some of the lower readings (55-70) were under the shade of some wood or other plants but still in the middle of the bulb area. So shade can have a dramatic affect.

So, I had readings of 15-20 at the feet of L. inclinata var cuba and this is a pretty thick bunch. All leaves are fine and green at the bottom, and get bigger, browner up top.

Same with L. aromatica with no algae and nice leaf formation.

The tops of the aromatica are about mid-water (12-14") and in a pretty close bunch. Taking readings at the plants tips ranged from 90-370 with the sensor never moving outside of a 4" circle. These are placed pretty much between two of the bulbs. However, one of my braces is in the middle of the bulbs.

Lower readings had smaller, greener, leaves. The highest readings were slightly taller, more colorful, and bigger leaves, but all were pruned level at the same time recently.

Surface:

I held the sensor directly under the water beneath one of the lights. Moving the sensor around slowly and letting the display 'settle', produced a range of 350-650 with the highest directly in the middle of the lens

Again, bringing the sensor just ABOVE the water, made a huge difference of at least 75-125 from just UNDER the water. This was consistent with placement.

So, very interesting stuff, and I am very glad I have this meter.

I totally recommend any club investing in one if they can.

So, surface to substrate under the one light produced a high of 650 at the surface and a high of 110 at the substrate directly in line. Well, close anyway lol

Will post more as I have it.

 

[jeremy v]

This is good stuff Gerry, thank you to you and the other people here (like Tom and others as well) that have performed other tests like this and posted your results here.

Lower readings had smaller, greener, leaves. The highest readings were slightly taller, more colorful, and bigger leaves, but all were pruned level at the same time recently.

That observation is interesting to me. I always assumed that leaves would be smaller when the lighting levels were higher, because the plants wouldn't need to have so much leaf area to get the light they wanted. Is there something I am missing here that is not being factored in that accounts for this discrepancy in my thinking? I have also heard that leaf shape, growth style, coloring, etc. was tied more to the intensity levels/balance of the blue and red spectrum of light rather than just intensity itself. If everyone else already realizes this stuff, forgive me, I am still pretty new to the actual "growing plants" part of the aquarium hobby.

Many of my plants (like amazon swords for instance), send their leaves up almost straight to the surface at the beginning. They only start to fold down (and provide the surface area necessary to absorb much light?) after more new leaves take up the center of the plant and push them from vertical orientation. I would also assume that leaves lose their ability to efficiently perform the work required of them as they age as well. My question is, which leaves are actually the most important and most beneficial for the plant in as far as taking in light?

Would there be much benefit to be gained in as far as plant growth and health by keeping the plant density a little thinner sort of like how you would thin a tree in your yard to ensure that light and air circulation reaches the leaves in the center of the tree to prevent fungal problems in the center of the tree etc? I would think it would work the same way for aquatic plants, but am I making an assumption that isn't true by thinking that?

I have also heard Tom talk about minimum light thresholds for plants. That all makes perfect sense to me. There is a minimum lighting level that a plant needs to meet its' minimum needs, but is there also a minimum light level that a particular leaf requires before that leaf can provide any benefit to the plant as a whole? Is that what mainly drives plants to shed older leaves, etc. or is the shedding of older leaves just because the new ones are more efficient at processing light and thus more beneficial for the plant?

Interesting stuff.

Have a good one, Jeremy

 

[Gerryd]

Jeremy,

NP. Happy to share it.

Ok, I'll jump in with my thoughts............

How about the theory that the importance of inner vs outer leaves, changes through the life of the plant. However, generally, I would say the larger leaves.

As an example with your swords, the new growth always starts at the center, or the growing tip. The outer leaves, as they are larger, are MORE responsible for nutrient retrieval than the tip, as these leaves need to produce for the entire plant.

I assume the tip can also assimilate, more as it grows, but am thinking that the growth rate of the tip is greater at first, and consumes more than assimilates. I think this equals out and goes the other way as the leaf grows.

As the outer leaves start to get older and larger, they fall outward, and they tend to die off and disintegrate. I think this is the plant eliminating older leaves that are now also consuming more, but contributing less. This also opens the growing tip to MORE light and nutrients, so it can take it's place in the cycle.

I know that the old rule to control large swords is to be ruthless with the new leaves, and not to let them get too large.

I think that by constantly trimming the larger leaves, you impact the overall ability of the plant to assimilate light and nutrients, and the TOTAL amount of nutes available to the plant is less, and it thus stays smaller.

The larger leaves have more surface area to catch light and intake nutes, so overall, I would say that the larger leaves are generally more reponsible for intake of all nutrients.

I also am finding that REGULAR pruning really makes a big difference. Stems tend to get thick very quickly, more so than we think. These areas tend to get very dark and lose a lot of flow. Less algae and better overall growth when a little thinner.

Thoughts? Or am I way out there on this?

 

[jeremy v]

Gerry,

That makes logical sense related to amazon swords, but I don't know where I could look to try to verify if that is actually truly the way it works. It does seem to fit with how plants will begin taking nutrients like magnesium from older leaves and transporting it to the new leaf tissue when in a condition lacking magnesium in the surrounding water. This leads me to another question as well, and possibly another once I get going, haha.

Everyone,

Corkscrew Vals were what led me to this question. I have just started growing those for the first time and so far I like the look of them, but they just stump me logically. Their leaves just grow and twist vertically straight towards the light and that's it. You would think that would be the worst possible way to grow for a plant to successfully absorb light, and yet that plant is doing fine so far (and beginning to send out runners) even in one of my 10g 1wpg tanks.

If you think about setting a plate flat on the ground outside in the sun (equivalent to plants like Ludwigia that put out leaves that are perpendicular to the aquarium light falling upon them), there will be a lot of the sun's light hitting a large surface area of leaves at a certain light level "X". Now set that same plate up on edge (the equivalent to having leaves that just grow straight up towards the light like Corkscrew Vals) and almost no light will hit the main surfaces of the plate at the same light level "X". The only way the plate's large surfaces could ever get much light would be if the sun was at a sharp angle, but aquatic plants never really get a sharp angle of light in nature, because any sunlight that penetrates the water changes to a more vertical and downward angle of light due to refraction, and anything over about 45 degrees from vertical just bounces off the surface of water completely.

What is going on there? Is something like a Corkscrew Val just so incredibly efficient at utilizing light that it can be perfectly fine with almost no intensity hitting the leaf surface even at higher tank lighting levels? And along the same line of thought, why doesn't Corkscrew Val just bend its' tips down a little bit so that the leaf surface can receive a whole lot more light and make the plant more efficient at any light level?

I knew I would end up having another question, haha. Do a plant's leaves actually have a finite life when all tank conditions are optimal and algae is not an issue, and if so what is it and does it change from plant to plant?

Have a good one, Jeremy

EDIT:

P.S.- The reason I am asking this stuff here instead of starting a new thread is not because I am trying to hijack your thread Gerry, but because I think it ties directly to it, so I hope you don't think that's what I am doing. I am thinking that if you are finding that plant growth, color, leaf shape, etc. all change just with light level changes of maybe factors of around 2-4x within the tank, wouldn't that imply that plants do noticeably adjust themselves for optimal uptake of light? If that is true then why is it that something like Corkscrew Vals never bother to do something as simple as bending their leaf tips down a little bit to catch more light on their leaf surface in order to increase their uptake efficiency? Maybe they do and I just haven't seen t yet, but I don't recall ever seeing Corkscrew Vals growing that way in any pictures of other people's tanks either.

I think that maybe I am still missing or misunderstanding a basic premise of how plants grow, but I can't figure out what that thing I am missing is, can anyone that is reading this tell by my questions and/or assumptions what it is that I am missing/misunderstanding?

 

[VaughnH]

I think that plants the bolt straight for the surface of the water do so in order to float on the water surface where both CO2 and light are the most intense. Most Vals, if left alone end up sprawled across the surface of the tank water, doubling back and forth as they continue to get longer and longer. Those leaves get great CO2 from the air, and the maximum light possible in the aquarium. Short vals, would contradict my theory, unless they evolved to grow in very shallow water.