It depends on what kind of a light day it is.
If it's a part of regular weekly programming, it's typically normal volume but lighter weight. For example, in a certain successful program I did a day of heavy volume squats, followed by a day of light volume squats, with an intensity squat day at the end of the week. As the light day was part of weekly planning, the volume was pretty high, tens of reps, but the weight was relatively low. It was skill practice, likely went into the hypertrophy level, but it was also restorative after the true heavy volume day before it.
If I want to take some light days for a longer period, a deload, like after a meet or a training cycle or in the middle of a tough training cycle, I go both lighter in weight and volume, and likely also change the exercises a bit. I find it's important to keep moving, using the whole body in a meaningful way. Total rest is a no-no, it makes me feel significantly worse and I 100% believe it's bad for me, like when a cycle gets harder it gets harder gradually, I believe it should be somewhat gradual in how it gets easier; so I keep moving, exercising.