Glaring means too bright, or too obvious to miss. A bare bulb, or a mistake on the first page.
The light sense is the older one, and glaring sunlight is the kind you squint against. The commoner modern use is about errors, and a glaring mistake, a glaring omission and a glaring inconsistency are all standard, meaning nobody could possibly have failed to see it. That gives the word a note of accusation. There is also a person glaring, which means staring angrily, and that is a different verb entirely.
Proto-West Germanic
*glāʀōn
Old English
*glærian
Middle English
glaren
English
glare
English, today
glaring
by surface analysis, glare + -ing. glare comes from Middle English glaren, from Old English glærian, from Proto-West Germanic glāʀōn. Cognate with dialectal Middle Dutch glariën (“to glisten; sparkle”), Low German glaren (“to shine brightly; glow; burn”), Middle High German glaren (“to shine brightly”). Related to glower, glass.
Etymology from Wiktionary, CC BY-SA