RAILROAD SIGNALS of the U.S.

LIGHT BULBS USED IN
 RAILROAD SIGNALING

and A BRIEF HISTORY OF LIGHT BULBS in GENERAL

What would railway signals be today if it was not for the development of the electric light bulb? 

Until the early 1900’s, kerosene lamps were used for illumination.  Railroads heralded the day electric light bulbs came around, because it saved them money, just like diesels did.  

A quick rundown of the history of the light bulb follows, and a good all around source for “how they work” is at the Living on Earth webpage. (7)

1800 - Humphrey Davy, an English scientist, experimented with electricity and developed a battery.  He connected the battery to a piece of carbon and it glowed.  First recorded incident of producing artificial light with an electrical source. (1)

1860 - English physicist Sir Joseph Wilson Swan devised a practical basic electric light. He used a carbon  paper filament, but it burned up quickly.  He demonstrated the new electric lamps in Newcastle, England in 1878.

1877 - American Charles Francis Brush made carbon arc lights to light a public square in Cleveland OH.  These lights were used on a few streets, in a few large office buildings, and even some stores. Electric lights were only used by a few people.

Note:  Carbon arc lamps are not the same as incandescent light sources.  Light was generated by an arc across two carbon rods.  The light source was very bright, and needed constant attending to as the carbon rods wore down.  An incandescent light source produces light as a result of the current flow through a material, mostly tungsten, causing the metal to glow.

1879 - American inventor Thomas Alva Edison discovered that a carbon filament in a vacuum (oxygen-free) bulb glowed but would not burn up for 40 hours.  He had experimented with thousands of different materials to find just the right one(s) that would glow well and last a long time.  He eventually produced a bulb that could last for over 1500 hours.  His patent was number 223,898, issued on January 27, 1880. (1)(2)

1881 - Lewis Howard Latimer (a member of Edison’s research team) improved the bulb by inventing a carbon filament.  In 1882, he developed and patented a method of manufacturing his carbon filaments.

1903 - Willis R. Whitney invented a treatment for the filament so that it wouldn't darken the inside of the bulb as it glowed.

1910 - William David Coolidge invented a tungsten filament which lasted even longer than the older carbon filaments.  We were off and running!

1962 - Nick Holonyak Jr., while at General Electric (Syracuse NY), invented the first practical light-emitting diode and the first semiconductor laser to operate in the visible spectrum.  He had worked with John Bardeen, who was one of the three co-inventors of the transistor. (3)(4)

1993 - Shuji Nakamura (a researcher at Nichia Chemical Industries in Japan) after years of research, produced the first commercially viable blue LEDs. (5)(6)

1997 - Nakamura produces the first white LEDs.

LED’s are stating to make some headway into the area of railroad signaling.  I saw an LED three color light signal on the (SB) Northeast Corridor in 2004, just south of Havre de Grace MD.  Their colors are pure, they use less electricity, and should have much longer life spans than incandescent light bulbs.  We’ll see.  I’ve seen far too many LED traffic signal lights that already have some bad LED’s.  And LED stoplights and taillights on trucks seem to “burn-out” even quicker!

Bulbs for signal illumination have been pre-focused for a long time, meaning the positioning of the filament is guaranteed, thereby eliminating the need for most focusing when the bulb is replaced. 

The following four scans are from the light bulb section (section "B") of a 1935 US&S catalog.

REFERENCES and ADDITIONAL READING:

1                    http://www.enchantedlearning.com/inventors/edison/lightbulb.shtml

2                    http://www.ideafinder.com/history/inventions/story074.htm

3                   http://www.ece.uiuc.edu/ingenuity/304/index.html    dead link

4                    http://www.pbs.org/transistor/album1/addlbios/holonyak.html

5                    http://itotd.com/articles/253/

6                    http://www.engineering.ucsb.edu/Announce/nakamura.html

7                    http://www.loe.org/series/LED.php

8                    http://science.howstuffworks.com/question244.htm  primer on Fresnel lenses

9                    http://www.du.edu/~etuttle/rail/sigs.htm well done primer on British signals (some American stuff too)

10                http://www.oksolar.com/led/led_color_chart.htm Great LED color chart/voltage drops/etc

11                http://theledlight.com/technical3.html Alternate version of the last reference

12                http://www.led.net/datasheets/Pages/chromaticity/097.htm dead link

13                http://www.led.net/datasheets/Pages/chromaticity/097b.htm dead link

14                http://science.howstuffworks.com/framed.htm?parent=question244.htm&url=http://micro.magnet.fsu.edu/optics/timeline/people/fresnel.html Link to bio of Fresnel

New 9/8/2005....
Last Updated: 02/10/2010