Exodus Exodus 10:1-29
At the ninth plague the God who said 'let there be light' says 'let there be darkness' — the same jussive, the opposite noun — and Egypt reverts to the uncreated dark while Israel keeps the only light in all of Exodus.
Revelation 21:23
The Lamb is not called 'light' in Revelation 21:23. He is called 'lamp' — a device that holds and transmits light from another source. John's vocabulary for light, luminaries, and radiance is remarkably varied, and the distinctions are not decorative. They are the theology.