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PHOTOCHROMIC GLASS
-it can change from transparent to coloured when it is exposed to ultraviolet   light   and reverts to transparency when the light is dimmed or blocked.
-it can be produced by embedding photochromic substances like fine silver chloride or silver halide crystals in glass or transparent polymers as the matrix.
-when exposed to light,the silver ion were converted to silver and the glass darkens.The photochromic glass become transparent again when the silver atoms lose electros to form silver ions when light is blocked.this is because the halogen formed during the decomposition of silver halide cannot escape from the glass,so it recombines with the silver atom in the dark and image fades.
-tha chemical can also undergo a chemical process that causes it to change shape.The new structure absorbs a portion of the light causing the lenses to darken.The number of atoms that change shape varies with the intensity of the light.

PHOTOCHROMIC GLASS IS USED TO MAKE:
a)optical lenses in glasses

   

b)car windshields
         

c)smart energy efficient windows in buildings
       

d)information display panels
     

e)photoelectrochromic panels for computers

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f)camera lenses

g)optical switches

                 

h)light detector devices

i)automatic light-control devices

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j)light intensity meters
-for measuring the intensity of light

                                                                       

-when   making lens and windshields,the photochromic glass helps
a)to protect oue eyes from harmful ultraviolet rays and glare from the sun
b)to control the amount of light that passes through automatically
c)our eyes to cope when they are exposed to different light condition
d)to reduce refraction of light