Our new method DaniReef LAB for PAR measurement
During the long nights spent on our forum (here) we always wondered how could we compare PAR from different ceiling lights. Even though we had the perfect device, the Quantum Meter MQ-510 di Apogee, we always referred only to the value measured at the centre at 20 cm of distance, more or less.
The Quantum Meter MQ-510 measures the PAR, expressed in PFFD that is photosynthetic photon flux density in μmol m-2 s-1. This device is calibrated to work underwater, so if it’s in air the measured value has to be divided by 1,32 that’s the dive factor. We have to do the conversion. The values you’re going to see are correct.
We decided to make a square base of 70×70 cm, we set 17 fiducial points where we placed the sensor Quantum Meter MQ-510 and we also made 3 lifts of 20, 40 and 60 cm for the ceiling light, in order to have the same distance from the sensor. This will allow us to create the curves which can be compared to other ceiling lights’s, all tested at the same distances. Notice that this distance is measured between the base of the sensor and the ceiling light. In reality it should be decreased of 3,5 cm that is the height of the measurement cylinder and increased by 0,5 cm that’s the dimension of the spacers that lift the ceiling light.
In total the three measurements are made from 17, 37 and 57 cm of distance. Because they’ve been done in air they will be corrected.
PAR measurement from 17 cm of distance
This is the condition of the test. Below there are the chart and the device, above the ceiling light placed on the aluminum bars.
Here the collected values:
And that’s the corresponding chart, we used the same scale for ceiling lights similar for power, that is if you see the chart of the Cetus 2, you’ll find the same rating scale.
Because this ceiling light is very close to the sensor and it is a single cluster the PAR decrease very quickly on the sides, as you can clearly see from the chart. It stands out that the peak value, measured in the middle, is superior to the Cetus 2, that has more power but prefered a more open lighting for a great coverage of the aquarium.
PAR measurement from 37 cm of distance
This is the condition of the test. Below there are the chart and the device, above the ceiling light placed on the aluminum bars.
Here the collected values:
And that’s the corresponding chart.
With a bigger space between ceiling lights and sensor, it decreases the difference between PAR in the middle and on the sides. The light spreads, but the central value decreases from 1256 to 281 μmol m-2 s-1.
It stands out that the coverage now it’s more complete.
PAR measurement from 57 cm of distance
This is the condition of the test. Below there’s the chart, from this distance the device it is very visible, and the ceiling light placed on the aluminum bars. Even visually the illuminated area is a lot wider, so the specific power per cm decreases.
These are the collected values:
And that’s the corresponding chart.
Increasing even more the space between ceiling light and sensor, it decreases even more the difference between PAR in the middle and on the sides. We have more uniformity, as expected, but the final power decreases a lot. The light spreads, while the central value decreases from 1256 to 281 to 123 μmol m-2 s-1.
Now the coverage is more complete.
The PAR in the middle in the different configurations
Let’s continue with our technical measurements. We can see how, in a chart, the PAR collected in the middle decrease in the three different distances of our tests.
Energy variation of the Aqamai LRS depending on the distances
This is the most significant and most comparable data: the energy variation. We calculated the volumes of the three surfaces previously seen. It’s obvious that moving away from the ceiling light the PAR decrease, also because the light illuminates a wider space. In this way you can consider all the light energy contained in the 60×60 cm area subtended by the ceiling light. An it’s clear that the three values of 275.881, 311.548 and 254.283 assume a different connotation compared to the values in the middle. When the first ones decrease because of the increasing of the distances, the subtended area, that is the energy, at first increases, because the main part is concentrated in the middle, then it decreases because part of it spreads all over the area.
In fact, looking at the values of the three curves you can see that at the sides there’s more light at 57 cm than at 37 cm.
Values per channel in the middle in the three distances
We also measured the values per each channel, but only in the middle, in order to give you an idea of the contribution of the different channels on the PAR produced.
Let’s see the measured values:
| Distance = 17 cm | Distance = 37 cm | Distance = 57 cm | |
| Channel 1 cool white | 336 μmol m-2 s-1 | 73 μmol m-2 s-1 | 32 μmol m-2 s-1 |
| Channel 2 green | 36 μmol m-2 s-1 | 8 μmol m-2 s-1 | 4 μmol m-2 s-1 |
| Channel 3 red | 130 μmol m-2 s-1 | 29 μmol m-2 s-1 | 12 μmol m-2 s-1 |
| Channel 4 uv and indigo | 58 μmol m-2 s-1 | 14 μmol m-2 s-1 | 5 μmol m-2 s-1 |
| Channel 5 royal blue | 373 μmol m-2 s-1 | 86 μmol m-2 s-1 | 37 μmol m-2 s-1 |
| Channel 6 cyan | 358 μmol m-2 s-1 | 85 μmol m-2 s-1 | 37 μmol m-2 s-1 |
The blues have an higher number of PAR than the whites, and Blue and Cyan are predominant for the PAR. The green doesn’t have a real impact.
Let’s continue on page three with the costs, the comparison with other ceiling lights and our final opinion.
