The Briggs & Stratton Corp., Milwaukee, Wis., a leading manufacturer of small, air-cooled gasoline engines, is continually looking for ways to reduce costs, improve product quality, and enhance product performance.

The same philosophy of the firm carries over into efforts toward improving its facilities. For example, the firm began to investigate a new area lighting source to improve visibility in the tool rooms, model shops, and inspection areas of the 1,700,000-sq-ft Large Engine Division plant.

To serve as the area light source, the company had been using 250W high-pressure-sodium (HPS) lamps, which have an average rated life of 24,000 hrs, plus excellent lumen maintenance over the long lamp life. However, the light output is mostly in the yellow, orange, and red region of the visible spectrum. As a result, the restricted color rendering characteristics of this light source made it difficult for tool makers and assemblers, who handle small intricate parts, to observe certain important characteristics of the materials. The HPS has an apparent color temperature of 2200 Kelvin.

Thus, the decision was made to retrofit each of the existing ceiling-mounted, open-bottom HPS fixtures with a 250W, base-up, replacement model, metal-halide (MH) lamp that offers better color rendition. For purposes of safety, the MH lamp has a shrouded arc tube design. Basically, the shrouded arc tube is a glass cylinder surrounding the arc tube; in the unlikely event of a nonpassive arc tube failure, glass fragments from the ruptured arc tube are blocked from hitting the outer glass bulb, thus preventing shatter. The open bottom fixture adds to the total efficiency of the fixture and allows lamps to be replaced using a lamp-changing pole.

The arc tube of the MH lamp contains, in addition to mercury, small amounts of other materials, such as scandium and sodium in a quartz arc tube. Thus, the MH lamp produces what is called a white light, and it has an apparent color temperature in the range of 2700 to 3500 Kelvin.

Based on the performance of the MH light source, 700 MH lamps were also retrofitted at the company's 280,000-sq-ft plant in Auburn, Ala. And at the 375,000-sq-ft plant in Statesboro, Ga., 900 MH lamps were also retrofitted to existing fixtures.