In my opinion, if people are able to sleep in darkness, they should, and it's not a good habit to start kids out sleeping with the lights on.
Why? I usually see issues going the other way, where kids from birth get absolute quiet and dark, then can't get to sleep without those conditions for the rest of their lives (i.e. adults who need blackout curtains and ear plugs to sleep).
Most sleep experts (including pediatric sleep experts) recommend blacking out your room, removing all electronics, etc.
Perhaps an expert in this area can chime in, but I don't think light during sleep is positive.
From an evolutionary biology standpoint, I would expect being able to sleep through light and noise a negative for survival.
By comparison, phone and laptop screens start around 400 lux and go up from there.
Many nightlights I've tried are at least 0.5 lux depending on distance, but are often higher (1 lux or more)
Given the wonders of dark adaptation of the human eye (https://en.wikipedia.org/wiki/Adaptation_(eye)#Dark_adaptati...), does that really matter? In my experience, the full moon is almost bright enough to comfortably read normal black on white printed text.
As a rough estimate, one decade (10x) of the eye’s light adaptation, at most, comes from aperture variation - the pupil expanding and contracting. The rest comes from intensity-driven modification of the sensing and image processing systems in the eye - rods that are completely saturated with signal above a few dozen lux become the primary sensors in very low light.
In other words - just because the moon provides enough light to see and even read doesn’t mean that it will cause insomnia.
It does make me worry how we'll wean him off the sound machine.
It has been shown[1] that even small sources of light can inhibit the secretion of melatonin (the hormone that regulates the circadian rhythm and consequently sleep).
If you use eyeshades, you might feel more rested in the morning (if your bedrooms is not already pitch black dark, that is).
As a personal anecdote, I always feel less rested when I don't use eyeshades.