| There are 2 different and unrelated to each other biological effects, related to blue light : Suppression of Melatonin production which affects sleep, and potential of "burn out" of S cone cells i.e. retinal damage
Both effects have a sensitivity curve for the effect, which is not just the same as the sensitivity curve of the S cone cell, but distinct and narrower curves. Specifically the melatonin production is controlled by a cell of its own altogether, not by the S cell
A light source can produce light which falls within the sensitivity band of the related biological effect, or which does not (by not emitting anything in that part of the spectrum at all, or by emitting more energy elsewhere in the spectrum, so that part becomes insignificant)
The quantity of light that gets into the eye (and takes part in vision and in triggering of the effects, if it is in the right wavelength) is "normalized" by the size of the eye pupil, according to the overall quantity of visible light. That works except when the pupil reach its limits in size and can't regulate the quantity of entering light anymore (in both ends of its range)
The question here is about the melatonin suppression effect. The answer is directly related to :
1. How much of the light emitted by the lamp is actually within the curve that affects melatonin production. The filters applied to GLS lamps are often of very wide band pass and often have also little attenuation of what's outside of the band (so, let through significant light even in wavelengths far from the let through band). The resulting light might have much more or much less light of the wavelength in question, compared to a 4000..6500K LED or Fluorescent light, all depending on the filter quality
2. How much light is emitted overall. The question was about a nightlight, so it might be putting out very little light in general (think ~0.1...1 Lux light levels in the area around the lamp) - such that is too little for the effects to have significant effect, even at the maximum size of the eye pupil
In the right combination of the 2 conditions ("not very good" filter + low light levels), the effect on melatonin may become less significant than some other effects that affect sleep quality of this person. For example, "higher level" (i.e. not as "low level" as the 1000's years old instincts), psychological effect like comfort of the individual person to sleep with/without the light, tendency to stay awake for longer or return to sleep faster if awaken in the middle of the night, and so on....
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