Ignorant question: Is the narrower bandwidth of light from LEDs a factor? (I don't really know much about light and optics and the human vision system, but I know in the audio world that pure sine waves can cause hearing damage at lower amplitudes than wider-bandwidth sound, and they can certainly sound more "piercing".)

This article refers to the LED light as "too bright, too blue, and too concentrated"--"too bright" and "too blue" are pretty clear, but "too concentrated" doesn't seem immediately clear to me--too concentrated spatially, I think it implied?, or too concentrated in discrete wavelengths?