The architecture of light: architectural lighting design concepts and techniques. A textbook of procedures and practices for the architect, interior designer and lighting designer pdfdrive com

The Properties of Metal Halide, Ceramic Metal Halide (CMH) and other High Intensity Discharge (HID) lamps:
Initial Cost: High;
These lamps represent a lot of technology packed into a small package. They are also fairly uncommon and therefore are relatively expensive.
Operating Cost: Cheap;
Like fluorescent, these lamps are efficient so they consume relatively little electricity and have long lamp lives requiring less- frequent maintenance and relamping.
Color Rendering Index: 70 - 90 (moderate to good);
Standard metal halide lamps have CRI values in the 70’s or 80’s. Ceramic metal halide can have CRI values in the 90’s and can provide pleasing color rendering properties. Other HID sources, like high pressure sodium and mercury vapor, have notoriously poor color rendering properties represented by CRI values of 30 to 50.
Color Temperature: warm to cool (pink to green);
Metal halide lamps tend to have a greenish or bluish cast regardless of the color temperature rating. Ceramic metal Halide lamps tend to have a pinkish or violet cast. All HID sources should be sampled prior to specification on a project, especially where color rendering is critical.
Ballast and Transformer requirements: Yes;
HID sources all require an electronic or magnetic ballast to operate. Electronic ballasts have desirable features like improved efficiency and less noise.
Dimming: seldom;
The dimming of HID sources is available, but can be quite costly. A lamp manufacturer’s representative should be consulted if dimming of HID sources is being considered for a project.
Instant on / off: No!
The most notable downside of HID sources is that they all require time to warm up. This time is shrinking as technology advances, but can be anywhere from 30 seconds to five minutes. For this reason, these lamps are primarily used where they will be left on for long time periods. When specifying HID sources, they should generally not be relied upon for instant-on operation.