Calvin cycle - Simple English Wikipedia, the free …

The coral was allowed to dark-acclimate overnight before minimum chlorophyll fluorescence (Fo) and maximum fluorescence (Fm - through application of a photosynthetically-saturating pulse of light) were determined. The coral was then exposed to light intensities that were incrementally adjusted upwards, and Fm' (maximum chlorophyll fluorescence while illuminated) measurements were made 15-20 minutes after light intensity was increased. Yields of Photochemistry, Non-Photochemical Quenching (of chlorophyll fluorescence) and NO (other energy dissipation pathways) were determined. When the Yield of any of these processes is multiplied by the light intensity level (PPFD, or Photosynthetic Photon Flux Density, as determined by a PAR meter), we can arrive at an estimate of the relative electron flow from Photosystem II to Photosystem I. The electron flow is called ETR for Electron Transport Rate. Since we did not measure the amount of light actually absorbed by the coral and its symbionts, this is called the Relative ETR, or rETR. The coral's zooxanthellae were allowed to acclimate to darkness for 20-30 minutes after each round of testing.

BioCoach Activity Concept 8: Cooperation of the Light Reactions and the Calvin Cycle

Far worse yet would be the cheaper no name emitters used by manufacturers such as BaiSheng, Epistar, & others sold under a plethora of other names for so-called aquarium use. These use daylight emitters that can vary widely in Kelvin Color output from only 2000K to 6500K and are in reality generally much less efficient for photosynthetic aquarium life use other than just plain light!

Think about why a CFL 10,000K daylight is so much different and more expensive than a common household CFL sold in hardware stores, or the many decorative LED aquarium lights or even those for home or flashlight use. Try using one of these to grow your delicate coral or plants (the answer is they will not without use of many). This is the reason most LED aquarium lights were not adequate for supporting life properly until about 2008-9.

The Sun is the star at the center of the Solar System

Here is a summary of lighting requirements for different aquarium types. I recommend timers for any aquarium to provide good daylight/night cycles, however this is even more important with Planted Freshwater and Saltwater Reef or Nano Reef tanks. Turn the actinic lights on about one to 1/2 hour ahead of the daylight bulbs and one to 1/2 hour later in the evening.
I generally have the brightest lights on for about 12 hours per day, with 1 or maybe 2 hours of less bright or "ramping" up or down of LEDs if used. Sometimes with MH I will have them in a third cycle that is on for only abut 10 hours or less.

Despite commentary in some aquarium keeping forums, there is NO evidence that ramping up and down much longer than 1 hour where strong lighting is used provides ANY benefit to plant growth, fish, or reef environments (this is not applicable where one low to moderate lighting is used and one on/off cycle is all that is needed).
I have personally kept many aquariums (100s) going back to where only timers were all we had and used single time one for strong lighting, partial tank on with full lighting an hour later, and multiple timers. While have partial lights on for an hour did produce results over a strong on/off, multiple cycles made NO difference!
Think of it this way; in tropical regions, there is little difference in bending of light rays from the sun much past an hour after sunrise or an hour before sunset, so thinking a ramp up/down cycle much more than this time will make a difference has no practical or scientific evidence to back this up.

For LED moonlight settings, generally just a 1-5% of your full lighting power setting is sufficient between main lighting cycles.
If you have separate moonlights, I would run these 8-16 hours (I have yet to find in benefit from this that can be scientifically proven other than aesthetics).

ANY fluorescent light used for aquarium applications such as planted aquariums or reef, slowly burns up phosphors and other rare earth elements that produce the light energy necessary for PUR.
As with a UVC bulb/lamp used for a UV Sterilizer, these lights go through a "half life", meaning that a light that is run 12 hours per day that may last 2 years (as per rated life) should be actually replaced every year otherwise these lamps are running at 50% and less of initial light energy production and then often producing much more yellow light and even an imbalance of red that is inducing to more algae and cyanobacteria growth in particular.

The picture to above/left clearly demonstrates the difference we can see with just our human eye between new 6400K Daylight SHO and one nearly two years old.
The color temperature of the old lamp/light.