On 21/02/2015 17:39, Tough Guy no. 1265 wrote:
On Sat, 21 Feb 2015 17:25:09 -0000, Tim Streater
wrote:
In article , Tough Guy no. 1265
wrote:
On Sat, 21 Feb 2015 07:47:09 -0000, harryagain
wrote:
"Tim Watts" wrote in message
...
On 20/02/15 17:05, Tough Guy no. 1265 wrote:
On Fri, 20 Feb 2015 16:26:40 -0000, Brian Gaff
wrote:
You can buy all sorts of luminous stuff nowadays - is there a
different
chemical that glows?
Yes
It's not luminous, it's phosphorescent.
https://en.wikipedia.org/wiki/Phosphorescence
No radioactivity involved
Ah. Although they aways say luminous on the product. I guess it's a
more
commonly known word.
Luminous covers all of the above; it's more general.
Phosphorescence to me makes me think of fluorescent tubes.
Fluorescent - when a substance absorbs a photon of UV or X-ray and
emits it at a longer (e.g. visible) wavelength.
Phosphorescent - light emitted by a substance without combustion or
perceptible heat e.g. glowworms or fireflies.
Luminous just means something is brighter than you'd expect given the
ambient light. It tells you nothing about how the object is producing
the extra light.
Phosphors in the tube fluoresce then, and not phosphoresce :-)
They do both. If you close your eyes first switch off and then look at
the tube in darkness you will see that it phosphoresces for a short
while after switch off. The modern generation of glo products use doped
Strontium Aluminate which is an astonishingly good long life phosphor.
The old glow in the dark stuff used zinc sulphide which was rather poor.
This glo torch is a particularly good example - after a day in sunlight
the torch plastic body emits enough light in total darkness to find it
by if the lights go out suddenly or to see by when dark adapted.
http://www.ebay.co.uk/itm/Glo-Torch-...-/181663763203
It will still keep glowing for several hours after exposure to the sun.
There are also the chemical glow sticks that use a combination of a
peroxide, dye and electron donor to generate cold chemical light.
--
Regards,
Martin Brown