PAR meter vs PAR sensor from Apogee

The readings of most interest to me are PAR at the substrate level in the center of the tank, or right below the light fixture (the thickness of the sensor above the substrate), at some specific distance above the substrate at the same middle location, and roughly how the PAR varies as you move from end and front to back. Of course, all of that for a given distance between the light bulb and the substrate. If possible, it is very useful to have the substrate level PAR with the fixture raised or lowered a specific distance. As I see it, those are the best data to standardize on, and the data that let you determine how high a given fixture has to be to get some PAR value.

 

Well its xmas in July. Sensor finally made it. Initial test with a m-meter and sensor seems to be intact. Modified a Kent Pro Scraper with a mount for measurements.

Those parameters for testing seem simple enough. I'll test my tanks this weekend. Talked with the lfs today and they are good with me coming in Monday and getting some data. There are seven different unique fixtures over display tanks that I can measure, from nano's to 80g, pc's, t5's mh, and hot5's. Which should give a good array of data.

 

try and take a note of the water clarity in each tank too. Can make a difference

AC

 

Just fiddled around before going out for the night and I'm somewhat amazed at what I figured was lower lighting. But it does re-affirm any advice I've given that 240w HOT5's over a 2ft deep 5ft tank is more than enough light. Center of the tank 20" below water line, bulbs 16" off the waters surface, and through 1/2" of acrylic. 70-75mmol's 160w 45-50mmol's.


I'm going to have to try alot of variations with this setup to help get a feeling for what raising / lowering a light fixture does in relation to par.

 

you'll probably find that having the light lower means very high PAR underneath the tube(s) and lower light in other areas.

Raising the light will definately reduce PAR directly under the tube(s) but more than likely you will see a more even spread across the tank and possibly evn find higher PAR in the areas that were showing low when the lights were lower down

 

Just initial logging is showing me that we highly underestimate our lighting. It really is no wonder so many people have so many problems when they are recommended lighting that is far far to much than is actually needed. HOT5's really do put out a great deal of light. Even my PC's in the 29 shocked me at the par levels, shallow tank yes, but still given the trend I'm seeing on fall off with distance, much higher than I would have thought.

THere definatly is a reduction, not a huge amount, but by percentage a noticable effect. Raising the light does definatly give you higher par in what where lower areas with the change in height of the lights. One interesting point has been much higher light at the substrate along the front edge of the glass with the lights raised.

I recorded today 10 different scenarios with the large tank and three scenarios on the 29. I won't have the luxury at the LFS since all their fixtures but one are fixed height. But the additional data of seven different light fixtures should give a nice range of data. Add that to Hoppy's and Tom's data and others on this forum, we should start to get a really good idea on light levels.

 

Very good data! I'm starting to plot your data, so please, do post your other PAR data too. Right now I am most interested in data at the center of the tank, under the bulbs, from substrate level on up. Nothing in the first three data points surprises me at all, and it tends to confirm my belief that the longer T5HO bulbs give about the same PAR at a given distance no matter which wattage bulb you have, with the longer bulbs needed to cover longer tanks.

 

I've got it all plugged into a spreadsheet. I'll be at the LFS tomorrow afternoon
and I'll update the spreadsheet then and post it up.

Data I'm collecting.


Tank Gallonage
Tank Dimensions
Light Manufacturer
Bulb Configuration (wattage and number of bulbs)
Bulb Type (ie PC or T5)
Distance / light to water surface
Distance / light to substrate
Par just under water surface center of tank
Par middle at center of tank
Par at substrate at center of tank
Par variation throughout middle region of tank
Par variation throughout substrate region of tank
US gallons inches inches inches umol umol umol umol umol

 

Bulb age! The one variable I always forget. Ideally all of the data any of us collect would be from bulbs 3-6 months old.

 

Or although its to likely possible, data from bulbs of many ages to see if they really do deteriorate as some people would have us believe or if they keep 95% of their PAR over 8000 hours as that article suggested r.e. maintaining 95% of lumens (on electronic ballast.)

AC

 

I'll add in bulb age. I'm gonna have to approximate mine at about 8 months. Due to actual usage from testing different scenarios for coloration (which is why I have a large selection of bulbs), and settled on a Aquaflora / Midday Mix. But I could purchase 3 aquafloras and compare new to old. Although I suspect like SuperColey there wouldn't be much of a difference. I think there might be more of a difference across cooled fixture and non cooled fixtures.

I was also suprised to see that the 1/2" acrylic doesn't do much to lower par. At an inch below the surface where I took all Top Center measurements, if I venture to the open area par only increased by 1 - 2 units. So not a significant difference.

I agree Tom. The advice for lighting really is a shame. Folks act like foregrounds or these so called high light plants were never grown before the advent of PC's or T5's. So we couple plant databases and advice that some plants are "high" light with miconceptions of how much light is actually in the tank, and we end up with people with lots of problems. Then they end up chasing nutrient deficiencies based on terrestrial plants that completely ignore Carbon and are factually incorrect in assumptions, and then you have more problems. Then you get the folks that just echo these things ... and the wheel keeps on turning.

Hopefully we can get enough data to see a trend. Then better advice can be given.

One thing that is very interesting to visualize with the meter. Is the effect of how par changes vertically. This is obviously more drastic in shallow tanks. If we look at how the levels change as far as percentages. You can easily have 50%+ gain in par over the span of a stem plant from planting to trimming. Then look at how that affects the need for Carbon. Now given our already high light, its easy to see how CO2 can be adequate early in the week and defecient later in the week. Then magnify that by a tank full of plants. Then add in to the thought process of flow and circulation. I can easily see now why you harp on CO2 and circulation as much as you do.

Hopefully as more data is gathered, we can also have a optimum distance between light and water surface. Now my tank will be different, due to spacing of the bulbs. I use alternating bulbs. Six bulb fixture and i only use every other bulb. I'll have to test that effect with just the center bulbs to simulate a typical four bulb fixture, since configurations here will have an effect.

 

An example of the changes in verticle par. I just trimmed the other day a stand of Limno Mini and replanted. Tops of the plants are at 55 mmol. From where I trimmed they were at 85 mmol. Thats a 55% increase in light intensity. Now what does that due to nutrient demand. These are issues to be aware of as things grow in, and how you might not have issues with CO2 one week but have them the next week.

 

The huge variation in PAR going from substrate to water surface is one good recommendation for MH lights, hung a good 24 inches above the tank. That height greatly reduces the intensity gain as the plants grow higher. I'm inclined to see the "perfect" light fixture as one that is the same outside dimensions as the tank, with many small lights (LED or full length T5 tubes?) evenly spread out over the entire fixture surface, with that fixture many inches above the tank. With this you get much closer to uniform intensity all over the tank.

 

Just got back from measuring. Pretty much what I expected as far as ranges. The ADA NA-Green bulb in a current fixture was interesting. The wide range with lights closer to the waterline was confirmed. Great deal of fall of around the corners and edges. The Tek 4 bulb was a shockers, I had to go back and confirm measurments on other tanks to make sure the sensor didn't get borked. After that re measured. Tons of light out of that fixture. Even two bulbs was a great deal of light.

I'll plug in the data and put it in a pdf for ease since I utilize OpenOffice and I'm sure not alot of people have MS Excel.

 

A pdf would be very nice. I'm not sure how to attach a pdf to a comment here though.

 

Made this easier than a pdf. Converted to threer file formats. An html document, OpenOffice document, a Excel 97 document. OpenOffice is a free Microsoft Office like suite. A pdf would be difficult for what you want Vaughn.

HTML
OpenOffice
MSExcel


Its just too much to fit into an image properly. I'll see what I can do on that end.

I missed this in the notes. GMix is a Geissemann mix of Midday and Aquaflora on everything but the IceCap fixture which is a mix of Aquaflora and Aquablue.

 

Thank you very much! I use a Mac Intel computer so I can open any of the three versions, and I have an Open Office program too. I chose to open the Excel version. Now, to have some fun plotting all of this stuff.