Implications of these tests:
This controlled test has aquatic implications, as photosynthesis is the same whether it be a terrestrial plant, a freshwater aquatic plant, or symbiotic zooanthellic algae found in corals.
The main difference would be that light energy is quickly absorbed by water, especially red light waves and many modern high-end LED fixtures such as an EcoTech Radion, AI Sol Vega Blue, ZetLight ZT 6600, AAP Fiji Blue, AAP Ocean Blue NP, and AAP Reef White 2000 produce the light energy for deeper aquarium water penetration more comparable to the popular 20k "Radium" Metal Halides.
An example of a new emitter developed just for photosynthetically sensitive reef inhabitants is the 'Osram Olson NP Blue'. This patented emitter primarily targets the FULL spectrum of blue necessary for phototropic response, as well it also contains light energy in the full spectrum of PAR, unlike other blue emitters that have come before it.
This is another concept to consider that we do not know all the "mechanisms" that drive it.
Basically photoinhibition is the damage to the light harvesting reactions of the photosynthetic capacity of a vascular plant, algae, or cyanobacterium by excess light energy trapped by the chloroplast.
This process can occur in in all organisms capable of oxygenic photosynthesis. In both plants & cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, although it has been demonstrated the red light can cause photoinhibition as well.
The implications for us as aquarium keepers is this process can often be the result of new light systems until our plants, photosynthetic corals, etc. adapt to the new light.
The point this makes/demonstrates is that while both lights are rated as 6500K, they are still not the same in their light energy output. Even among LED lights we can have differences of spectrographs depending upon emitters used.
Think about how mixing all paint colors will produce black, while the mixing of all light energy produces white. We as humans may notice this to some degree, however we do not have the ability to pick out particular colors such as a honey bee can. As well, photosynthetic aquatic life also has differing abilities to pick out the needed light energy for life processes and even though the PAR readings may be equal, the light energy that provides this overall PAR or kelvin "color" is NOT.
The picture to the left demonstrates this with two 15 Watt CFL (30 watts total) vs one 3rd generation 12 Watt Marine White LED (daylight 14,000K).
This picture is taken with a camera that filters out certain wave lengths allowing for a better viewing of the difference, which is otherwise not easy to discern. However, the picture shows how the LED on the left has less of the less efficient yellow & green than the CFL lights on the right.
Otherwise the light output appears the same, although this is still important when you consider, this is achieved with only 12 watts of LED vs 30 watts of Compact Fluorescent lights.
The picture below shows a spectrograph of two 6500K aquarium lights. One is an AAP AquaRay GroBeam and the other is a 6500 Aquarium CFL. The LED is rated at 12 watts while the CFL is 13 watts.While similar, it is clear to see the LED has more blue and a lower blue NM (fuller blue spectrum) amount as well as more red, less green, and the same yellow.The point this makes/demonstrates is that while both lights are rated as 6500K, they are still not the same in their light energy output. Even among LED lights we can have differences of spectrographs depending upon emitters used.
Think about how mixing all paint colors will produce black, while the mixing of all light energy produces white. We as humans may notice this to some degree, however we do not have the ability to pick out particular colors such as a honey bee can. As well, photosynthetic aquatic life also has differing abilities to pick out the needed light energy for life processes and even though the PAR readings may be equal, the light energy that provides this overall PAR or kelvin "color" is NOT.A Couple more points to better explain the concepts of PUR, "Useful Light Energy", or "Quality of light per application".
For further reading about PUR:*Below is a picture of a Reef Aquarium (88x32x24) that includes Acropora corals lighted with ONLY VERY high PUR but lower wattage AAP AquaRay NP 1500 & 2000 LED lights (this tank has been running with these lights for 6 months at the time of the picture).
The picture above depicts both full solar radiation that reaches the earth as well as how a few different man-made light sources fit into the visible/PAR aspect of this spectrum.
What is noteworthy is how much radiation falls outside the PAR, in particular the longer frequency wave lengths going into radio waves. There is much that we also do not know, since photosynthetic plants, zooanthellic algae, etc. might also be using radiant energy we do not know about. What we do know is that since UVC is not reaching the earth's surface and that even UVB only reaches in small amounts (if at all during certain times of the day and seasons), that it is likely this is mostly useless for our application.
While PUR also encompasses this too it also can simply refer to all light spectrums within PAR with emphasis on the more efficient spectrums rather than the less efficient spectrums such as yellow & green. Or stated another way, the portion of PAR, which is more efficiently absorbed by plants & zooxanthellae photopigments thereby stimulating photosynthesis. We can state PUR one more way, where as PAR is the most important quantity of light, "PUR is the quality of light as per application".
Another term is . I should point out that while the terms PAS & PUR have a lot in common, there is a difference in that PAS is most simply stated as the spectrum where "chlorophyll is much more efficient at using the red & blue spectrums of light to carry out photosynthesis. Therefore, the action spectrum graph would show spikes above the wavelengths representing the colors red & blue."
Many people will think PUR is good in theory, but think it cannot be applied to every single species we are trying to grow under water. While we don't know every species and it's preferred nm of light prefers, we do know the light, which triggers photosynthesis in an organism as well as efficiencies based on real world tests.
PUR cannot be dismissed as some lighting experts have attempted to do based on their short time in the professional aquarium keeping industry, as we have already clearly established (as per the Overview section) that we found that once more precisely tuned spectrum fluorescent lights became available, we could grow aquarium plants more efficiently and with some advancements, this made the difference of not keeping photosynthetic marine organisms at all!! I should note that some of these advancements were comparing apples to apples; T12 to T12 such as a warm white to a Trichromatic or an actinic (which rules out lumens per watt and other measurements and leaves the FACT of PUR).
PUR (Photosynthetically Usable Radiation) is something aquarium keepers should concern themselves with along with PAR in providing correct lighting since it describes the quality of light photons as per application.