In General
Special Bulbs


In General

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

Until the early 1900’s, kerosene lamps were used for illumination.  Railroads heralded the day electric light bulbs came around, mainly because it saved them money, just like diesels did, but more importantly, it made signals easier to see.

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)


Major Milestones in the Development of the Electric Light Bulb and LED's

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.


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.



LED’s are starting to make some headway into the area of railroad signaling. 

There are a number of "trilight" style colorlight LED signals on the (SB) Northeast Corridor, just south of Havre de Grace MD.  I first noticed them in 2004.

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!

Here are some examples from around:

LED's in use on the Houston Light Rail System, 2007

LED "tri-light" signals on the NEC at Havre de Grace MD, 2008

An LED colorlight signal on the Light Rail System in Charlotte NC, 2010

A LED colorlight signal on the Atlanta MARTA Metro system, 2006

An interesting signal installation on the NEC in Wilmington DE.  If you notice, the pedestal signal on the left is illuminated by LED's.  The one on the right, has two incandescent bulbs in the upper position, and an LED in the bottom.

Special Bulbs

Every industry has their special application bulbs, the railroad industry is no exception.  Here are a few.

The little pear shaped neon lamp, a General Electric type NE-40, came from the little repeat coil board in the Reading's Chester passenger station, and was on a telephone circuit.  The lamp was probably used as a ring indicator for 90 volt 20 cycle ringing current.  It probably dates from the 1940s. It has been "in storage" for 34 years.  Courtesy ADB.

The tubular lamp, a Western Electric type 7A, came from the UD Wire Chief's Office in the Harrisburg station, where it was used as a ballast resistance on the 22A repeater circuit and was probably installed new when UD was built in 1937.  It has been "in storage" for 25 years.  Courtesy ADB.

Both of the above "lamps" have Edison bases and measure only 3.25" tall.

Note: My source was in the middle of installing a new 160 mil telegraph circuit, and was looking for some current-limiting protection.  He pulled these out of storage.


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.homeadvisor.com/article.show.The-History-of-the-Light-Bulb-in-Your-Home.17366.html    nice non-railroad page with many good links, thanks to Erica B and her class for this 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://science.howstuffworks.com/framed.htm?parent=question244.htm&url=http://micro.magnet.fsu.edu/optics/timeline/people/fresnel.html Link to bio of Fresnel



I love trains, and I love signals.  I am not an expert.  My webpages reflect what I find on the topic of the page.  This is something I have fun with while trying to help others.  My webpages are an attempt at putting everything I can find of the subject in one convenient place.  There are plenty of other good websites to help me in this effort, and they are listed in my links section on my indexa page, or as needed on individual pages.  Please do not write to me about something that may be incorrect, and then hound the heck out of me if I do not respond to you in the manner you would like.  I operate on the "Golden Rule Principle", and if you are not familiar with it, please acquaint yourself with how to treat people by reading Mathew 7:12 (among others, the principle exists in almost every religion).  If you contact me (like some do, hi Paul) and try to make it a "non-fun" thing and start with the name calling, your name will go into my spambox list! :-)

If this is a railfan page, every effort has been made to make sure that the information contained on this map and in this railfan guide is correct.  Once in a while, an error may creep in, especially if restaurants or gas stations open, close, or change names.  Most of my maps are a result of personal observation after visiting these locations.  I have always felt that a picture is worth a thousand words", and I feel annotated maps such as the ones I work up do the same justice for the railfan over a simple text description of the area.  Since the main focus of my website is railroad signals, the railfan guides are oriented towards the signal fan being able to locate them.  Since most of us railheads don't have just trains as a hobby, I have also tried to point out where other interesting sites of the area are.... things like fire stations, neat bridges, or other significant historical or geographical feature.  While some may feel they shouldn't be included, these other things tend to make MY trips a lot more interesting.... stuff like where the C&O Canal has a bridge going over a river (the Monocacy Aqueduct) between Point of Rocks and Gaithersburg MD, it's way cool to realize this bridge to support a water "road" over a river was built in the 1830's!!!   Beware: If used as a source, ANYTHING from Wikipedia must be treated as being possibly being inaccurate, wrong, or not true.

My philosophy: Pictures and maps are worth a thousand words, especially for railfanning.  Text descriptions only get you so far, especially if you get lost or disoriented.  Take along good maps.... a GPS is OK to get somewhere, but maps are still better if you get lost!  I belong to AAA, which allows you to get local maps for free when you visit the local branches.  ADC puts out a nice series of county maps for the Washington DC area, but their state maps do not have the railroads on them.  If you can find em, I like the National Geographic map book of the U.S..... good, clear, and concise graphics, and they do a really good job of showing you where tourist type attractions are, although they too lack the railroads.  Other notes about specific areas will show up on that page if known.

Pictures and additional information is always needed if anyone feels inclined to take 'em, send 'em, and share 'em, or if you have something to add or correct.... credit is always given! BE NICE!!! Contact info is here

Beware: If used as a source, ANYTHING from Wikipedia must be treated as being possibly being inaccurate, wrong, or not true.


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Last Updated: 02/17/2015