single case, where two or more lamps were contained within a single cast housing, and the modular light, where each lamp was an independent unit capable of being arranged into a signal of arbitrary configuration, including triangular. US&S has a popular single case type with its styles R/R-2, P-2/5 and N, while GRS offered their triangularly arranged Type G, with the Chicago Signal Company providing a similar version. Today's Safetrans Triangular is a copy of the GRS Type G but with vertically arranged double doors. Signals like the model N/N-2 could also be mounted directly on the ground as a dwarf signal without a backing. The most notable user of this type of signal was the Chesapeake and Ohio, but units could be found on railroads all over the country. Over time, due to its low cost and versatility, the modular color light signal became the standard in North America. The first modular system was the GRS Type "D", first marketed in 1922, and adopted by the Southern Railroad along with many others: D&RG, etc. The GRS units used a smaller "background" than the comparable US&S vertical possibly somewhat compromising long range visibility. Today the most popular type of new signal in North America is a modular design manufactured by Safetran, as it is the cheapest, with all of the four major Class 1 railroads installing it almost exclusively. Today, both GRS and Safetran market separate modular systems for high and dwarf signals, while US&S uses the single modular Style "R-2" design for high and Style N-2 for dwarfs. Modular color lights allow for all the cost savings inherent in color lights, but also make it easier for railroads to stock signals and perform alterations to interlockings. Instead of having to order custom heads, new modules can be taken from stock to build new signals or modify existing heads.With simple bracketry, even triangular color lights may be built up with these standardized components. Modular color light signals are often fitted with a full-length sun shade which improves visibility in bright sunny conditions. This shade was originally adopted by the Union Pacific and Denver Rio Grand and Western railroads to prevent snow buildup on one shade from obscuring the signal lens above it. Position light signals Position light signals use rows of diameter lamps to simulate the positions of an upper quadrant semaphore blade. Position lights were developed by A.H. Rudd,