the bright shining of the sun
暐 centers on the bright, shining light of the sun. It describes the sun's radiance itself, not just a sunny day.
暐 combines 日 (sun) with 韋, which likely contributes the sound. The character is used to express the bright shining of the sun.
The sun 日 on the left shines brightly, and the right side 韋 looks like a radiant, spreading pattern. Together they show the sun's brilliant shining.
For イ, imagine the bright sun shining on an easel: easel -> イ, and the sun's light makes the painting glow.