Welcome to You Ask Andy

Don Walker, age l0, of Chicago, I11,

An ordinary light bulb of clear glass gives a bright, yellowing light  A fluorescent lamp is usually a long tube of milky colored glass  It glows with a daytime dazzle of white light, it gives off less heat than an ordinary light bulb and it uses lass electric current  In the ordinary bulb, the light comes from the small metal rods inside the glass, In the fluorescent tube, the light is made by the milky coating on the inside of the glass  The electric current jostles this light  giving process into action 

This strange process is called fluorescence  There are certain substances which glow in the dark or give off a light which is not their true color  A diamond may glow for a moment after the light is turned off  Thick yellow sometimes shows a rainbow on its surface which is not its true color  When a glass of chlorophyll, which is the stuff which makes plants green, is held up to the sunlight it shows a bright red color  In the world of chemistry, this quality of showing false colors is called fluorescence 

A fluorescent material may absorb some of the rainbow colors of white light and send back false colors or it may send back false colors when exposed to ultraviolet rays  These are the rays of sunlit which are too short for our eyes to see  Hence, some fluorescent materials seem to shine in the dark where there is no visible light 

The inside of a fluorescent light tube is given a coating of one of those materials  The next trick is to start it glowing and for this we need a steady stream of electrons  Ordinary air is removed from the glass tubs and replaced with a mixture of argon gas and mercury vapor  At each end of the glass tube there is a metal sap with two plugs to link the tube with the electric wiring 

On the inside of each metal disk, there are two metal rods joined with a coil of very fine wire  These are the electrodes, sealed inside the tube and connected with the electric wiring outside the tube, The magic starts when you turn on the switch and the electrodes begin to warm up with the electric current 

Soon a stream of electrons is flowing back and forth between the two electrodes  They dog back and forth perhaps 60 times a seconds In the hurry and scurry they dog the molecules of argon gas and mercury vapor in the glass tube, There are collisions  These agitated electrons, streaming between the two electrodes excite the mercury vapor in the glass tube 

This agitation and excitement causes the molecules of mercury vapor to give off ultraviolet rays  The ultraviolet radiation, invisible to our eyes, strikes the flourescent coating on the inside of the glass tube and causes it to glow with the white brilliance of daylight

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