A home made glow discharge lamp
 Electrical discharges through air are the first 
kind of clean artificial light. 
 The rarefied gas electric discharge tube was 
discovered by Nollet in 1740. 
 Further work was done on this lighting 
technique by Faraday, Geissler  and Edison 
before the end of the 19Th. century. 
 With the help of Sprengel's Mercury siphon 
vacuum pump of 1865 the development of the 
illuminated city of night began.
  Close-up of a neon 
sign tube.
 Until the appearance of this article, making such a lamp required the use of an
expensive and highly specialized kind of air pump that could be found only
in well equipped school science classrooms, research labs, industry, and
certain fortunate hobbyist's homes.

 The soft glow of the rarefied gas lamp is a highly expanded form of an electric
spark.   The following shows the effect of reducing the air pressure to allow
the discharge to expand.


  An electric spark is held small by the pressure of the 
surrounding air. The discharge shown here has about  
2500 volts across the electrodes with a current of about 
4 miliamps. The current limit is set by series resisters. 

  As the air expands, the 
spark becomes larger and fainter.  The amount of 
power is fixed,  so it is is spread over a larger volume. 

 As the air is given more room by the pump, 
the discharge will fill and be stopped by the chamber 

               Constructing a simple discharge tube and setup.

 Note, plans for a simple power supply are underway.  There are plenty of
books  and perhaps some people around schools who have knowledge that can
lead  the building of high  voltage power supplies of the kind needed for this

 The voltages used here are potentially dangerous. Connect clip leads between
the lamp and the supply terminals before plugging in the power supply.
 Cartridge fuses of this type are a good source 
of short lengths of small diameter glass tubes. 

 Get a number of fuses to practice on. 
 Grasp the fuse with a slightly damp heavy 
duty paper towel.  Place the tines of a fork 
against the inner edge of the cap on the other 
end and push gently outwards while bringing 
the fuse end over a lit candle. The glue and the 
solder should melt and the cap slide off. 
 Repeat  for the other end.

 Clean the remaining glue from the glass 
tube ends with acetone-moistened paper 
 Make sure to clean all lint and moisture 
from all mating surfaces. 
 Assemble in a dust and lint free area. 
 Silicone grease could assist assembly 
and sealing. A solid 1/4" Dia rod can be 
used instead of the soldered tube segment 
as shown to the right side of this picture.
 The tube is ready for connection to the 
pump and power supply.
  Old tube type lasers are now obsolete and many of the tubes have 
gone bad.  Now many of the power supplies are unpaired with no 
further purpose.  Surplus dealers and some flea market venders sell 
them for a buck. 

 These electrical connections should be made before applying power. 
  Small power supplies can deliver quite a jolting shock. Hazard comes 
not only from the effect of the electricity, but also injury from hitting 
one's self against surrounding things and other people nearby. 

  Do not leave out the 25 K ohm series ballast resister.  
This resister reduces the current and prevents it from rushing or 
surging out of the power supply in bursts. 
 These power resisters come a glazed ceramic tube ranging from a 
little over an inch 3/8" dia for a 10 watt to a 25 watt one of 4 inches 
long by 5/8 th.of an inch dia. 




  Rarefied  nitrogen gas gives off 
a violet light when a current 
passes through it.  This turns to a 
pale blue gray when water vapor 
given off by the internal surfaces 
of the setup, replacing the dry

  These pictures were taken when 
I had a shorter glass tube section. 

 There is a considerable, but 
harmless amount of long wave ultraviolet  light from this setup. 
The glass  of the tube blocks the 
harmful short wave ultraviolet 

 An experiment was tried using a 
quartz tube with the rarefied air 
discharge. It still did not produce 
short wave uv. A mineral 
prospector's uv lamp and a 
postage stamp was used to verify
that tube was quartz. 
 More on this later. 

 As the air becomes more 
rarefied,  the discharge assumes 
a peculiar striated appearance


  This electrical discharge is 
affected by magnets.  
 Here is a current flowing in a 
gas which is free to move about. 
 Just as an unconstrained wire 
near  a strong magnet moves 
when a current passes trough, 
this discharge will show the 
magnetic deflection principle. 

 The larger tube shown here has 
a white phosphor on its lower 
inside surface for the electron 
beam to excite.


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