熹 describes the faint warm light just before sunrise, classically in 熹微 (dim early light). It also appears in the historical name 朱熹, the Song-dynasty Neo-Confucian philosopher.
The fire radical in its four-dot bottom form, from 火. It supplies the meaning: warmth and the glow of light, here the first warm light of dawn. It groups 熹 with 热, 煮, and 照.
The large element on top supplies the sound (xǐ shifting to xī). It contributes pronunciation only; the bottom element carries the meaning of light and warmth.