Unclear how large of an effect is has, probably less than removing blood and irradiating it, since that process doesn’t have to balance against eye damage.
However I think the major difference is going to be the intensity of the dose. Cells get through the retina and sclera pretty quickly, less then a second, and UV from sunlight isn't actually that intense on the ground (3mW/cm^2 [0]). Dosing in the paper ranges from .1W/cm^ to 200W/cm^2 for anywhere from 10 seconds to 30 minutes. In the minimum case this is ~5 orders of magnitude more UV.
On a side note, I really dislike the default layout of NIH reports. I always have to pick the classic or PDF to be able to read them.
[0] - https://ag.tennessee.edu/solar/Pages/What%20Is%20Solar%20Ene...
"Vitamin D deficiency is worldwide a prevalent health problem and has health impacts on about one billion people. Deficiency or insuffciency of vitamin D is common in the US population, mainly because of inadequate dietary intake, sedentary lifestyles, and reduced sun exposure"
https://www.researchgate.net/publication/292995237_Vitamin_D...
and similar conclusions in many other academic publications.