If I stay in the shade or indoors, I’ll be totally protected, right?
On a bright, cloudless day, from about 11:00-16:00 (11am to 4pm), maybe not. In these conditions, even an umbrella with SPF 50+ protection can be negated by exposure to light and heat reflected from the sand (or snow), water, and shiny objects.
Indoors, as much as 50% of UV light can get to you via sunlight streaming in through windows, accidental exposure when traversing open spaces, and bouncing off reflective surfaces.
Remember, too, that it’s not just outdoor light that causes skin damage: indoor Visible Light (fluorescents, halogens, even computer screens), and Infrared Light (heat from cooking, saunas, etc.) can cause hyperpigmentations. This is why Armada tests its formulations specifically for protection against both outdoor and indoor light (still the only sun + light screen to do so).