Asymmetric Tri-Lights

 When one thinks of the North American tri-light signal configuration (circular target with the lamps clustered in a triangle) one might assume that if the lamps are not set in a single large housing they would consist of single lamp modules kit bashed into a triangle instead of a vertical stack. For the most popular color light signal modules, the Safetran CLS-20, this is the case, however over the years the industry has produced some modular tri-light designs that don't use a common lamp module.

Of course I was prompted to write this post after being confronted by a tri-light product from our old friends at L&W. Purchased by Amtrak for its New Haven to Boston "Shore Line", this tri light has a single lamp module at the bottom with a double lamp cast aluminum housing above. From the front it looks like three singles due to the characteristic gap in the middle, but closer inspection reveals the true configuration.

 

 

The second example is from Transcontrol, a company typically associated with active grade crossing equipment. Somehow they were part of the contract to re-signal Hoboken Terminal around 1984 and their tri-light solution involves two standard lamp modules above an extra large one, which I assume serves as a junction box for the whole assembly. (Note, until this post I was unaware that Transcontrol made signal hardware and I might follow up with them in the future if more information presents itself.) 

One might consider the crop of asymmetric tri-lights to be offshoots of the original US&S style "TR", which features a single cast iron housing with three individual lamp sockets. Signals need terminal blocks to connect the interior wiring to the external wiring and terminal blocks take up space.

If you're wondering how the CLS-20 does it, there are openings on top at the 11 and 1 o'clock positions that match with other openings at the 7 and 4 o'clock positions. For a tri-light configuration the lamp modules are mounted 4 to 11 and 7 to 1. A supplier who can handle both vertical and tri-lights with a single SKU is naturally at an advantage so as a result the asymmetric tri-light has faded into history.