Does Lux trigger when you reduce a spell's cost below 5 with Eager Apprentice?

Ruling: Yes, Lux triggers based on the printed/base cost of the spell, not the reduced cost you actually pay.

Nuances:

• Cost reduction effects like Eager Apprentice reduce the cost you pay, but do not change the base cost for trigger purposes
• This principle applies to other similar effects like Defy and blue Kai'sa, which all check printed cost on the card
• This is different from "ignoring cost" effects, which reduce the base cost to 0