Interesting thoughts shared. Perhaps we'll agree to disagree here.
There is no harm from sunlight and very likely benefit no matter what lat and longitude a person lives. The bleaching argument makes no sence, deepwater acros are maricultured alongside other acros. UC had a post discussing this.
Just to be clear, the OP isn't lighting the tank with sunlight only. There will be no browning of coral here.
Natural is and always will be 'in.' The arguement isn't if a glass box is natural.
No benefits to sunlight? For real? If kessils grew coral better than the sun coral farmers would take advantage of this so called supreme technology. Where does the term full spectrum even come from, the sun. Our lights are simply trying to balance coral health, growth, and aesthetically pleasing color.
Perhaps I need to clarify - bleaching is a risk if you have a tank set up for artificial light and you add sun. I run my acros at 600 PAR, the sunlight here is 1000 PAR right now give or take. If I was to just open up my windows those coral would have 1600 PAR on them if I do not turn off my lights. Since PAR should really be thought of as cumulative through the day even if I turn off my lights while the sun is shining I could exceed what coral can handle over the photo period if I run the lights at night or the morning. Now you have deep water acros or lps and while yes they can take some higher PAR that is a whole lot to throw at anything. We are not talking about a system that was specifically designed to use sunlight, we are talking about open an existing system to allow sunlight to hit it.
I am not a kessil fan, however you can't blanket say artificial light is worse than the sun for growing coral - a large argument to using the sun is economics - it's free.
If we get into the bleaching factor a bit more - we have very poor flow in our tanks compared to the ocean, high flow reduces the boundary layer of water which allows the coral to dissipate extra heat faster - and heat is how coral deal with excess illumination. We can already light our tanks to provide more energy than they get in nature, adding sunlight might not be the best idea. Look at the article to the Daily Light amount.
http://www.advancedaquarist.com/2013/9/aafeature
Not saying you can't supplement with sunlight but be aware of the challenges and don't think it's just an easy win.
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. Our tanks our maintained at fairly stable temps. This is just simple Physics with thermodynamics. Adding sunlight in some instances may increase heat but we are talking from a window, not solar tubes or in a green house. The reason tanks arnt lit by sunlight is because of logistics and ability to funnel and direct light. It's has nothing to do with too much PAR or heat.

