Metal Halide Lamps
Metal Protected Lamps: offer a high degree of safety for open fixtures and those with plastic lenses. These lamps are designed with a shroud over the arc tube that prevents the outer glass envelope from breaking in the event of a "non-passive" arc tube failure. Open fixture technology has allowed fixture manufactures to design a wide range of fixtures in which no cover glass is required. By far the most common application is for downlighting, but other uses such as decorative lighting are also beginning to appear.
The open fixture rating allows for greater flexibility in fixture design, lower fixture costs and improved maintained lumens through the elimination of glass lenses. These lenses are costly to install and become collection platforms for dirt, dust and bugs.