Harmful Radiation When a Thinly-Veiled but Evident Sun is Directly Viewed Under Haze or Cloud Cover When it is hazy or overcast with many thin fast-moving clouds, the sun sometimes appears faintly though the cover---making it possible to be observed without any discomfort. In fact, one could easily look at the veiled sun for an extended period of time as if they were viewing an eclipse without protective eye-wear; which leads me to the question:
QUESTION: Can the continuous viewing the sun when it is thinly veiled by haze or cloud-cover be harmful to the eyes; or is the same harmful radiation still penetrating into the eyes that would cause the same effect as if one stared continuously at a total eclipse of the sun without eye protection? If one can safely view the thinly veiled sun---then what causes the reduction in harmful radiation?
Thank you.
 A: The big issue with such a situation is that you only get two eyes.  It would be unfortunate to err against caution, and find onesself blind.
Indeed, a thin layer of obscurant will obscure the sun's rays some.  How much?  Well that depends on that specific day's definition of "a thin layer," and how much you are willing to trust that it was "enough."
Definitely worth noting is that the eye is susceptible to heating caused by wavelengths outside of our visible spectrum, but our pain reaction is limited to only wavelengths inside of our visible spectrum.  So if your particular obscurant on your particular day obscures visible light more than, say, infrared light, you can get into a situation where your natural aversion to painful light is insufficient to protect your eyes.  How to tell if this obscurant has this property?  No idea.  From what experience I have with IR photography, your intuition about what is clear or opaque has nothing to do with how clear or opaque that object is in various infrared bands.
So can it happen?  Sure.  Would I ever trust my own eyeballs to it, or recommend others trust their eyeballs to it?  Not without a lot of background and a lot of expensive sensors to gather the data.
