High pressure sodium lights conserve energy and provide improved lighting at lower cost at Spencer Yard, Southern's newest classification yard, near Linwood, N.C.
At Spencer, 300 high pressure sodium lights of varied wattage do the job that in older similar installations required 1,200 mercury vapor lights to illuminate a huge classification yard. At the same time, 92 high pressure sodium lights do the work of 142 mercury vapor lights inside Spencer's large mechanical shop.
The project is the first use ever of high pressure sodium lighting throughout an entire yard facility by a U.S. railroad. The result is an initial installation saving of $500,000 over mercury vapor, and a projected energy cost saving of $70,000 a year at this one location - enough energy to meet the needs of 70 average households for more than a year.
Although high pressure sodium had been used by Southern previously to replace lighting at other locations, the designers of Spencer Yard drew it into their plans, thereby assuring that Southern would receive the maximum possible benefits.
In the past, lighting was designed largely on the premise that a certain amount of illumination would be available, so, in effect, the job had to fit the light. With the higher efficiency and versatility of sodium lighting, this concept was changed to "make the light fit the job." Thus lighting was designed to accommodate any given "seeing" task any - where in the yard.
Concentrated and projected
As a result, Spencer Yard takes advantage of both distributed lighting, where illumination is concentrated as needed in a relatively small area; and projected lighting, where fixtures are mounted atop high steel towers and "throw" light over a wide area where general illumination is needed.
Since high pressure sodium lamps are about two and a half times more efficient than the same wattage of mercury lamp, a large part of the cost of saving ( other than initial installation) comes in the reduced amount of energy required to operate the system. But there is another element of cost saving - the fact that the versatility and controllability of high pressure sodium permits the best use of an appropriate type of fixture in the right place.
And cost savings go even further. Southern has already found that maintenance is significantly lower than on mercury vapor lighting systems. The company has calculated that of the projected $70,000 - a - year saving, 20 percent is reduced maintenance cost and 80 percent power savings (based on existing power rates that are bound to increase). The maintenance saving results from having fewer fixtures, lamps and transformers to maintain.
Moreover, as part of Southern's modern system, a maintenance worker is not required to climb a high tower to change a lamp, but merely stays on the ground and operates a mechanical lowering device that brings the fixture and lamp down to him.
Shop lighting automatic
In the high pressure sodium system that lights the large locomotive and car repair building at Spencer, even further energy savings are gained from the use of an automatic energy controller, which in effect is a light dimmer. With automatic control, rather than introducing light at 100 percent output with more light than is necessary and having the level diminish as lamp lumen and dirt "depreciation" set in, a level of lighting can be selected, then power to the system gradually increased to overcome the effects of depreciation.
This system permits light output to be controlled from low to high, or varied from 20 percent to 100 percent of the rated output of each fixture. When mixed with "ambient" light from outside, the light can be controlled automatically at a predetermined level.
At 60 percent rated output at night, the lighting load is less than one watt per square foot, yet provides a very adequate 90 footcandles. As daylight comes, lamps are dimmed to only 20 percent of rated output, with the same results. In cases of cloud coverage in the daytime, the automatic energy controller "sees" the situation and - after a slight delay to allow for a small cloud quickly passing - produces the prescribed 90 footcandles of light.
Towers of power
Besides this feature of the inside lighting system, and the fact that the outside yard lighting system can be mounted on towers rather than hang from the more complex and expensive catenary, versatility also is achieved from the fact that fixture designs can vary from point to point, helping obtain maximum efficiency in the face of dirt, dust and other environmental factors.
Inside the maintenance facility, for example, it was found that lamps totally enclosed in dust tight fixtures would better withstand the typically industrial atmosphere. The larger yard lighting system, by the same token, employs enclosed fixtures at some locations and open fixtures at others.
As a bonus to the energy and maintenance savings inherent in high pressure sodium lighting, Southern has found two special areas of the Spencer Yard operation where it has proved particularly advantageous.
One is the closed circuit television system that records and monitors the identification of cars going through the yard; the other is in the freight car inspection pit in the maintenance shop, where close inspection of car underbodies is required. In both applications, Southern has found high pressure sodium lighting to be a very effective source.