Contemporary Rolex watches (like the one pictured below) use a photo-luminescent material on their dials and hands, which means that modern watches will glow in response to light exposure. The intensity and duration of glow is directly proportional to the amount of light exposure that the watch receives; a watch that is kept inside a safe or under the sleeve of a jacket will not glow at all in the dark, while one that receives plenty of direct sunlight will glow brightly, long into the evening.
Prior to the widespread implementation of photo-luminescent material, Rolex used a radioactive compound called Tritium to make their hands and dials glow in the dark. Since Tritium is radioactive, it will glow whether or not it receives any light exposure; however its ability to glow is limited by the radioactive half-life of the material itself. This means that as Tritium ages, its ability to glow will diminish until the point that it ceases to glow at all.
Rolex adopted Tritium as a safer alternative to Radium (another radioactive material); however since Tritium is significantly less radioactive than Radium, it only has a half-life of approximately 12.5 years. This means that roughly two decade after the watch was originally manufactured, only a small fraction of its initial luminescence would still remain.
Consequently, it is only natural for an older Rolex watch (like the one pictured below) to not glow anymore, as the radioactive material that was originally used on its dial and hands has effectively burnt itself out over the years. Additionally, since the loss of luminescence is due to the inherent limitations of the manufacturing materials, a non-glowing dial and handset is not often seen as a demerit when determining potential resale value.
As far as restoring the luminescence on an older watch that no longer glows, it is possible; however doing so requires that the dial and hands either be “re-lumed” or replaced – there is no way to simply “recharge” the pre-existing luminescent material. Re-luming is an aftermarket process in which a photo-luminescent compound is applied to the dial and hands in place of the non-glowing Tritium. Alternatively, a watch’s luminescence can be restored by replacing both the dial and hands with later-era equivalents that rely on photo-luminescent material to provide the parts with their glow.
A glowing watch does possess a functional advantage over its non-glowing equivalent; however most vintage Rolex watches have lost their ability to glow, and it is simply considered a trait that is consistent with older timepieces.