The light Erry's using is a light spell they cultivated. While a simple spell, the light it produces is clear and bright, and would be quite a luxury if they purchased it from another mage.

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Transcript:

P1: Erry reads their book quietly as a moth is drawn to their reading light. 

P2-3: The moth bumps into the light several times, producing a soft 'tmp' with each impact 

P4: Erry shuts their book as their attention sets on the annoying moth.