Left-side sun radical - pictograph of the sun, originally circular with a central dot, regularised into a small rectangle with a horizontal line inside. The indexing radical, naturally so:
晖 is sunlight, sunshine, the slanted golden light of dawn or dusk (
春晖 spring sunshine,
余晖 afterglow). Same sun/light family:
明 bright,
晨 morning,
晚 evening,
暖 warm,
暴 sudden-violent.