Re: [photo-3d] BULBS

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

To answer Sy's question, the following light bulbs will work
in a variety of stereo viewers:

Bulb No.   Type   Voltage  Current
--------  -----   -------  -------
no. 14    Vacuum   2.5 V    0.3 A
no. 245   Vacuum   2.5 V    0.5 A
no. 222   Vacuum   2.33V    0.27A
no. K222  Krypton  2.33V    0.6 A
Halogen1  Halogen  2.5 V    0.5 A
Halogen2  Halogen  2.5 V    0.8 A

The bulbs in this list meet two requirements:

- They are rated 2.5 V to be compatible with two-cell operation
of most stereo viewers.  Most viewers use two D size cells.  A
few viewers use C size cells.

- They have a screw base (also known as E-10 threaded base).  Today
most flashlights use bayonet or flange bases.  This is a problem.
For example, most of the common halogen and krypton flashlight
bulbs CANNOT be used in stereo viewers because they do not come
in a screw base (E10).  The halogen bulbs listed above are made
in small quantities for applications that require this screw
base (like our stereo viewers) that's why they do not have an 
official number and usually cost more.

A few more comments:

- Light bulbs are characterized by their voltage (V) and current
(measured in A) ratings.  Some bulbs also report luminosity and
life time.  The product of voltage times current is the electrical
power consumed by the bulb.  Most of this power is converted into
heat and a small only amount is converted into light.  This power
will show you how fast the bulb will consume the batteries.

- Some bulbs are filled with a special gas (krypton, halogen)
which does two things:  Allows the bulb to operate at a higher
temperature, resulting in higher light output.  Extends the
filament's life.

- For all these bulbs which operate at the same voltage (2.5V)
the higher the current, the higher the light output as a rule.
So the halogen 0.8A bulbs is brighter than the 0.5A no. 245 
bulb, which is brighter than the 0.3A no. 14 bulb.

- The no. 14 was commonly used in the 50s and it is still 
available today (you can buy it at Radio Shack, for example)
Because of the low light output, it is not a good choice for
stereo viewers today unless if low light output is desired
(ask Mark Dottle :-)) or for compatibility with transformers 
from the 50s or to save on batteries.

- The no. 245 is a popular replacement for the no. 14.  It 
is noticeably brighter and quite inexpensive.

- The 222 bulbs are "prefocus" type bulbs, i.e. they have a
lens at the top to focus the light, something that is useful
for flashlights that do not have a reflector to focus the light.
If you use them in a stereo viewer, make sure that the top
(when the beam is focused) is painted white, so this high
light intensity is not wasted.  The K222 would seem to be a 
good choice, being bright and inexpensive, but note my previous
comments regarding the short life and variable performance.

- The halogen bulbs are made under special order to come
with the desirable screw base.  I can supply two intensity
ratings, 0.5A and 0.8A.  The 0.5A is brighter than the
no. 245 and will be gentle to your batteries.  The 0.8A
is still for me the best choice.  These halogen bulbs
as part of the manufacturing process they have a little
nipple at the top, which makes them taller than standard
bulbs.  In the bulbs that I sell, I remove this protrusion
so these bulbs can be used in all viewers.

To be continued....

George Themelis


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