sunrise, sun's rays
暾 centers on the first light of day: the moment of sunrise and the early rays of the sun.
暾 combines 日 (sun) with 敦, which likely contributes the sound and may carry a sense of warmth or fullness, together suggesting the sun's early warmth at sunrise.
The sun 日 rises beside 敦, a shape that looks like a person offering something warm. Picture the sun offering its first warm rays at sunrise.
For トン, imagine the sun rising with a deep, warm tone: tone -> トン, and the first rays spread across the sky.