Luminous Green

[SRobb]

Why are luminous things (signs, clock hands, toys) always green?

[marylou2]

If they were red, would you ask why they were always red?

[Mortartube]

Because the radioactive elements used in many luminous paints emit light in the green part of the spectrum.

[Mortartube]

Actually, I've just found this which explains how luminous paints work http://www.blacklite.com/Technical/Luminous_Concep
ts.htm

[Hamish]

Just to clarify. 'Luminous' paints today are not radio active, although it has been used in the past esp for watch faces. If it is radio active then it will retain its brightness indefinitely in the abscence of light.

as Mortartube points out in the second answers link, the effect in paints today is phosphoresance which results in the slow (some times very slow) resuction in emmited light with time. High energy light (blue) is absorbed and lower energy light (green) emitted. It is easier to see green than red in the dark so this is better for signs etc. Hope this helps.

Hamish