Lights as they apply to aquarium use have evolved/changed considerable since I have been in the hobby & professionally employed in aquarium set-up & design.
We often used "hardware store" warm white T12 fluorescent lights, just in larger "quantities" to make up for the poor "quality" of light, even while planted freshwater could be kept, not so with ANY photosynthetic reef life.
Early on lights such as the "Aquarilux" came out which still was heavier on the "warm" colors, it also had more blue.
Later the Trichromatics & Triton lamps came out with spectrums focusing on the daylight 6500 Kelvin temperature, these made growing planted aquariums easier with less lights to do the same job as earlier lights.
We also had actinic blue lights become available, these mixed with other lights made it possible in the beginning to keep some photosynthetic reef life, although initially these did not thrive. Later T6 & T5 advancements along with Metal Halide lights allowed us to not only keep delicate photosynthetic reef life, but for this life to thrive.
We now have T2, SHO, & LEDs of which the later have lowered considerably the input energy for the quantity of output energy of light that we need for our aquarium keeping applications.
This is why often comparing one 6500K lamp to another can often be "apples to oranges" as for necessary useful light energy (PUR) needed by plants or corals. Another reason why Kelvin ratings are often poor methods to rate modern aquarium lights.
When sea levels rise as dramatically as they did in the Cretaceous, coral reefs will be buried under rising waters and the ideal position, for both photosynthesis and oxygenation, is lost, and reefs can die, like burying a tree’s roots. About 125 mya, reefs made by , which thrived on , began to displace reefs made by stony corals. They may have prevailed because they could tolerate hot and saline waters better than stony corals could. About 116 mya, an , probably caused by volcanism, which temporarily halted rudist domination. But rudists flourished until the late Cretaceous, when they went extinct, perhaps due to changing climate, although there is also evidence that the rudists . Carbon dioxide levels steadily fell from the early Cretaceous until today, temperatures fell during the Cretaceous, and hot-climate organisms gradually became extinct during the Cretaceous. Around 93 mya, , perhaps caused by underwater volcanism, which again seems to have largely been confined to marine biomes. It was much more devastating than the previous one, and rudists were hit hard, although it was a more regional event. That event seems to have , and a family of . On land, , some of which seem to have , also went extinct. There had been a decline in sauropod and ornithischian diversity before that 93 mya extinction, but it subsequently rebounded. In the oceans, biomes beyond 60 degrees latitude were barely impacted, while those closer to the equator were devastated, which suggests that oceanic cooling was related. shows rising oxygen and declining carbon dioxide in the late Cretaceous, which reflected a general cooling trend that began in the mid-Cretaceous. Among the numerous hypotheses posited, late Cretaceous climate changes have been invoked for slowly driving dinosaurs to extinction, in the “they went out with a whimper, not a bang” scenario. However, it seems that dinosaurs did go out with a bang. A big one. Ammonoids seem to have been brought to the brink with nearly marine mass extinctions during their tenure on Earth, and it was no different with that late-Cretaceous extinction. Ammonoids recovered once again, and their lived in the late Cretaceous, but the end-Cretaceous extinction marked their final appearance as they went the way of and other iconic animals.
The ecosystems may not have recovered from Olson’s Extinction of 270 mya, and at 260 mya came another mass extinction that is called the mid-Permian or extinction, or the , although a recent study found only one extinction event, in the mid-Capitanian. In the 1990s, the extinction was thought to result from falling sea levels. But the first of the two huge volcanic events coincided with the event, in . There can be several deadly outcomes of major volcanic events. As with an , massive volcanic events can block sunlight with the ash and create wintry conditions in the middle of summer. That alone can cause catastrophic conditions for life, but that is only one potential outcome of volcanism. What probably had far greater impact were the gases belched into the air. As oxygen levels crashed in the late Permian, there was also a huge carbon dioxide spike, as shown by , and the late-Permian volcanism is the near-unanimous choice as the primary reason. That would have helped create super-greenhouse conditions that perhaps came right on the heels of the volcanic winter. Not only would carbon dioxide vent from the mantle, as with all volcanism, but the late-Permian volcanism occurred beneath Ediacaran and Cambrian hydrocarbon deposits, which burned them and spewed even more carbon dioxide into the atmosphere. Not only that, great salt deposits from the Cambrian Period were also burned via the volcanism, which created hydrochloric acid clouds. Volcanoes also spew sulfur, which reacts with oxygen and water to form . The oceans around the volcanoes would have become acidic, and that fire-and-brimstone brew would have also showered the land. Not only that, but the warming initiated by the initial carbon dioxide spike could have then warmed up the oceans enough so that methane hydrates were liberated and create even more global warming. Such global warming apparently warmed the poles, which not only melted away the last ice caps and ended an ice age that had , but deciduous forests are in evidence at high latitudes. A 100-million-year Icehouse Earth period ended and a 200-million-year Greenhouse Earth period began, but the transition appears to have been chaotic, with wild swings in greenhouse gas levels and global temperatures. Warming the poles would have lessened the heat differential between the equator and poles and further diminished the lazy Panthalassic currents. The landlocked Paleo-Tethys and Tethys oceans, and perhaps even the Panthalassic Ocean, may have all become superheated and anoxic as the currents died. Huge also happened, which may have and led to ultraviolet light damage to land plants and animals. That was all on top of the oxygen crash. With the current state of research, all of the above events may have happened, in the greatest confluence of life-hostile conditions during the eon of complex life. A recent study suggests that the extinction event that ended the Permian may have lasted only 60,000 years or so. In 2001, a bolide event was proposed for the Permian extinction with great fanfare, but it does not appear to be related to the Permian extinction; the other dynamics would have been quite sufficient. The Permian extinction was the greatest catastrophe that Earth’s life experienced since the previous supercontinent existed in the .
While oxygen level changes of the model show early fluctuations that the model does not, both models agree on a huge rise in oxygen levels in the late Devonian and Carboniferous, in tandem with collapsing carbon dioxide levels. There is also virtually universal agreement that that situation is due to rainforest development. Rainforests dominated the Carboniferous Period. If the Devonian could be considered terrestrial life’s , then the Carboniferous was its . In the Devonian, plants developed vascular systems, photosynthetic foliage, seeds, roots, and bark, and true forests first appeared. Those basics remain unchanged to this day, but in the Carboniferous there was great diversification within those body plans, and Carboniferous plants formed the foundation for the first complex land-based ecosystems. Ever since the episodes, there has , and the that have prominently shaped Earth’s eon of complex life probably always began with ice sheets at the South Pole, and the current ice age arguably is the only partial exception, but today’s cold period really began about 35 mya, .
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.
*Phototropic response; having a tendency to move in response to light. Basically this is the Chlorophyll containing plant or algae "moving" to respond to a positive light source to begin the process of photosynthesis (initial growth of plants, zooxanthellae, etc.).
*Photosynthetic response; During this time, the molecules needed for photosynthesis gradually reach operating levels which begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls.
PAR is the abbreviation for Photosynthetically Active Radiation which is the spectral range of solar light from 400 to 700 nanometers that is generally accepted as needed by plants & symbiotic zooanthellic algae for photosynthesis (Zooxanthellae are single-celled algae that live in the tissues of animals such as corals, clams, & anemones).
It is also noteworthy that while outside of the accepted PAR, a study using infrared (IR) LEDs of 880 nm & 935 nm on etiolated oat seedlings showed leaf emergence, so these parameters may someday need better defining (See at the end of article).
*Chlorophyll synthesis; occurring in chloroplasts, this is the chemical reactions and pathways by the plant hormone cytokinin soon after exposure to the correct Nanometers wave length , that traps the energy of sunlight for photosynthesis and exists in several forms, the most abundant being Chlorophyll A.
This results in continued growth of a plant, algae, zooxanthellae and the ability to "feed" & propagate. Without this aspect of PAR, zooxanthellae & plants cannot properly "feed" propagate resulting is stunted freshwater plant growth, and eventually poor coral health in reef tanks.
This is also known as the Photosynthetic Action Spectrum (PAS).
*Chlorophyll A; A type of chlorophyll that is the most common photosynthetic organisms predominant in all higher plants, red & green algae higher plants, red & green algae. It is best at absorbing wavelength in the 400-450 nm & 650-700 nm
*Chlorophyll B; The chlorophyll that occurs only in plants & green algae. It functions as a light harvesting chlorophyll pigment that pass on the light excitation to chlorophyll a. It absorbs well at wavelength of 450-500 nm & 600-650 nm
Since many photosynthetic organisms live where light in higher spectrums of PAS such as 600nm & higher penetrate less if at all (in particular algae, zooxanthellae, & cynaobacteria), many have adapted to ways to still harvest this light energy.
These organisms use Phycobilisomes which are light harvesting antennae of photosystem II (Chlorophyll synthesis in the Photosynthic Action Spectrum-PAS).