Bulova 0S20 series, Settings Manual

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WATCH DIAL AND HAND LUMINESCENCE
The industry uses a luminescent material that is “charged” by light only. It is
non-toxic, is activated by light, emits a bright glow for a short time after
being charged, but also shows a steady reduced glow for a longer period.
Activation is made by exposure to daylight or artificial light. The strength of
this glow is following a specific curve: very high in the very beginning, after
the first significant drop-off, the brightness is reduced gradually, until the
material stops emitting light after several hours. The effectiveness of the
material is dependent on the amount of exposure to light, the thickness and
area of the luminous material and the fineness and the color of the base
material.
All phosphorescent materials emit a bright glow for only a short time period,
then a faint glow for an extended period of approximately six hours. After
the initial high glow, the luminance drops to one seventh within 30 minutes.
The intensity is further reduced to about 1/40th of its initial value after five
hours.
Our night vision is what sees the luminous glow after the initial brightness is
reduced. However, our night vision needs time in darkness (usually several
minutes) to adapt to the darkness. At this time the reduced glow should
become visible.
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