Ceramic metal halide (CMH) lamps work better with Square Wave Technology ballasts. Higher emissions and longer life with less decay of emission in time. This bulbs usually came with a optimal blend of gasses in ceramic arc tubes, producing a full-spectrum white light with a color-rendering index (CRI) between 90-93 (sunlight has a CRI of 100 and an HPS lamp is about a 26).
CMH lamps are available in a full-spectrum, 30/3100 K version and in a high-blue spectrum, 4,200 K version that is better for vegetative plants. A 315W CMH can easily replace a regular HPS 400W offering same or higher emissions and longer life. If used with a Square Wave electronic ballast a 315W CMH can emit even more PAR than an HPS, offering an interesting Price/emission/energy use balance.
The lamps offer also longer lifet with two-year, 20,000-hour replacement recommendation. CMHs produce more light per watt than single-ended HID lamps. Replacement of your older single-ended HID light systems, will lower your electrical bill and the overall heat-load in your garden while maintaining the same light intensity at the plant canopy.