Leo Lichtman wrote:

The inverse square law (not inverse cube) does mean that the amount of light
per unit area decreases with distance, but that is not the end of the story.
The light reaching a lens is collected and focused on the image plane.

A lens can't collect and focus more energy than is intercepted by it's
total area.

The further out you go from a spherically radiationing source, the less
the incident power density, and so the less total energy incident on a
lens of fixed diameter.

However I could see the energy density of a welding arc at substantial
distance, multiplied by the area of the lens, and then concentrated
onto a small area of the retina still being dangerous.