I apologize if it seemed that I was saying sunlight will sterilize surfaces. That is not what I described.
I didn't precisely say sunlight would totally sterilize a Corona virus contaminated surface, either.
I said prolonged sunlight exposure greatly dimishes cultured colony counts of bacteria and fungi on sun exposed asphalt surfaces - That is a fact. The effect is almost certainly due to the UV light within sunlight. Dessication MAY play a role too,
Do I suspect strong direct sunlight for a few hours in mid-day reduces viral counts on exposed surface - Yes, I am pretty certain it does. Is bleach more effective - almost certainly.
Would I suggest soap and hot water as more effective than sunlight? Probably, if done routinely, and is even possible. I can let my mail lie in the sun for a few hours; washing it in hot soap and water will probably destroy it - the mail I mean.
I do know that strong UV light is very effective at decontaminating exposed surfaces. The University of Nebraska Medical Center used it to decontaminate Ebola contaminated patient rooms a few years ago, and is currently exploring its use in decontaminating used face masks, due to the extreme face mask shortage currently occurring.
Should we all be wearing face masks, versus just the walking ill? Despite govenments attempts to suggest standard surgical masks are not much help, there is much credible evidence they can be of significant value in pandemics - most Asian citizens are wearing masks, and with pretty good reasons, as described in this article by the New York Times.
There are facts, truth, and generally but not always totally true facts. Is it better to never re-use masks?? Yes, if you have enough that you never run out of masks. But if you don't have enough masks, which is better? Going without, or re-using decontaminated masks? Questions we in the West never thought we would seriously be asking ourselves.
Is sunlight more effective than nothing at reducing viral loads on contaminated surfaces? I believe it is, but to truly answer this required carefully culturing mutiple spots on the surface of treated versus untreated surfaces in multiple cell cultures, and then counting the results.
A long, complex, and expensive study that I suspect probably has not even been performed, since the goal with Corona virus is total decontamination which requires a viralcidal technique of some sort.
What we DO KNOW, is that UV light ( of sufficient strength, exposure, wavelength ) DOES decontaminate Ebola surfaces if done appropriately.