Short answers, pulled from the story.
Sunlight takes about 8.3 minutes to travel from the surface of the Sun to Earth. A photon originating in the Sun's core, however, may take between 10,000 and 170,000 years to work its way to the surface before making that final journey.
At Earth's surface, sunlight is approximately 49.4% infrared, 42.3% visible light, and 8% ultraviolet. Above the atmosphere, sunlight is about 30% more intense and the ultraviolet fraction is also around 8%, but with a higher proportion of biologically damaging short-wave UV.
Sunlight drives vitamin D3 synthesis in the skin, supports normal circadian rhythms, and is associated with lower rates of high blood pressure and cardiovascular mortality. Insufficient sun exposure is linked to 340,000 deaths per year in the United States and 480,000 deaths per year in Europe. Overexposure causes sunburn, skin cancer, cataracts, macular degeneration, and immune suppression.
Sunlight intensity decreases inversely with the square of the distance from the Sun. At Mercury's closest approach, solar radiation can reach 14,446 watts per square metre; at Neptune's orbit the maximum is just 1.54 watts per square metre. At a distance of about 500 astronomical units, sunlight would be as dim as full moonlight on Earth.
The solar constant is the amount of incoming solar electromagnetic radiation per unit area at a distance of one astronomical unit from the Sun. Its value is approximately 1,361 watts per square metre, though recent satellite recalibrations revised it down from an earlier estimate of about 1,366 W/m2. Space-based measurements since 1978 show it varies with the 11-year sunspot cycle and with longer cycles including the 88-year Gleisberg cycle and the 208-year DeVries cycle.
UVB radiation, spanning 280 to 315 nanometres, directly damages DNA and causes sunburn, but is also required for vitamin D synthesis in mammalian skin. UVA, spanning 315 to 400 nanometres, was once considered less harmful and became the basis of cosmetic tanning booths, but is now known to damage DNA indirectly through free radicals and reactive oxygen species and can cause cancer. UVC, from 100 to 280 nanometres, has germicidal properties but is almost entirely absorbed by the atmosphere before reaching the ground.