The huǎng reading covers dazzling light and fleeting time: 晃眼 (dazzling), 一晃 (in a flash), 银晃晃 (gleaming silver). The physical 'sway / shake' sense uses the sister reading huàng.
Sun radical on top. For the huǎng reading the sun is literal: 晃 is the glare of bright sunlight, hence 'to dazzle' and the fleeting 'flash past'. The same radical sits in 明, 暗, 时.
Bottom 光 gives the sound and reinforces the meaning: sun plus light equals brilliant glare, exactly the huǎng sense of dazzling brightness flashing into the eye.
