On its own 荧 is rare; you'll usually meet it in compounds: 荧光 (yíngguāng, fluorescent light), 荧屏 (yíngpíng, TV/computer screen), 荧荧 (yíngyíng, glimmering). The original meaning is the faint light of a candle or firefly.
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Spot the 艹 (grass) radical on top — a hint at its old link to 萤 (yíng, firefly), which has the same lower component. Both come from the image of tiny lights flickering in grass at night.
艹 is the indexing top grass radical, but here it is graphic residue from the simplification of 熒 — the original had two 火 stacked at the top, and the 1956 reform compressed that double-fire into the simpler 艹 silhouette. Read it as stylised flames, not literal grass.
冖 is the cover radical, a flat lid drawn across the middle. It separates the flames above from the fire below — picturing a shielded flame, the kind of hooded glow that lights up softly in the dark. The whole graph reads as a covered light, fitting 荧's firefly meaning.
火 sits at the base in its full standalone form — the literal fire under the cover. Together with the flame-residue 艹 above and lid 冖 in the middle, it completes the lantern-glow picture: a shielded blaze that becomes the metaphor for fluorescent light and firefly luminescence (荧光, 荧屏).
