Challenge 1: Animating a Light Switching Instantly On and Off — Solution Walkthrough

The answer:

Per this chapter's own material, Constant interpolation fits this need
directly. It holds a value fixed at one keyframe's own setting, then
jumps instantly to the next keyframe's value with no transition at
all — exactly the instant on/off switching described here.

Why Linear or Bezier wouldn't produce the same effect:

Per this chapter's own material, Linear interpolation changes a value
at a steady, constant rate between keyframes, and Bezier eases
smoothly in and out — both would produce a gradual transition between
the light's off and on states, rather than the instant, hard switch
being asked for. Neither matches the requirement of no transition at
all.

Why Constant is specifically named for this kind of effect:

Per this chapter's own material, Constant interpolation is described
as useful for a strobe-light effect or a hard, deliberate snap —
precisely this scenario of a light switching states with no gradual
transition in between.

WHY THIS WORKS AS AN ANSWER
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This exercise checks that an instant, no-transition state change is
correctly matched to Constant interpolation, distinguishing it from
Linear's steady rate and Bezier's smooth easing.