CMH (Ceramic Metal Halide)

CMH (Ceramic Metal Halide), marketed as LEC (Light Emitting Ceramic) by Sun System and Phantom brands, was the bridge technology between traditional HPS/MH and modern LED. CMH emerged in the early 2010s and dominated serious indoor cultivation from 2014-2019 before being overtaken by full-spectrum LED. The technology: CMH bulbs use ceramic (rather than quartz) arc tubes that operate at higher temperatures and pressures, allowing more complete combustion of metal halide salts and producing broader, more sun-like spectrum output. Standard CMH sizes: 315W (the most common size, ideal for 4×4 ft canopies), 630W (commercial-scale double-ended fixtures, equivalent to 1000W HPS coverage); 400W and 1000W variants exist but are less common. CMH operating characteristics: light output 100-130 lumens per watt with PAR efficiency 1.7-2.0 µmol/J (better than HPS, lower than modern LED); spectrum is full-spectrum sun-like with peaks across 400-700nm range plus UV-A output (315nm-400nm) that traditional HPS lacks; operating temperature still high but lower than HPS — bulb surface around 700°F; bulb life 20,000+ hours (longer than HPS); bulbs degrade more slowly than HPS, retaining usable output through life. CMH advantages over HPS/MH: full-spectrum output suitable for both vegetative and flowering (one bulb, no swap needed), UV-A output enhances terpene production and trichome density, more efficient than MH and HPS individually, longer bulb life reduces replacement frequency, more natural-looking plant color under CMH (HPS makes everything look orange-yellow). CMH advantages over LED (in 2014-2018 era): lower upfront cost (CMH fixtures $300-500 vs equivalent LED $800-1500 in that era), proven reliability and consistent results, no risk of LED driver failures or chip degradation. CMH disadvantages: lower efficiency than modern LED (1.7-2.0 µmol/J vs 2.5-3.0 µmol/J), still significant heat output requiring cooling, bulbs require ballast equipment, fixed spectrum vs LED dimmability and spectrum tuning. The CMH market peaked around 2018 and has declined as LED prices fell and efficiency increased. CMH remains popular among growers who prefer the proven HID technology and want UV output without paying premium LED prices, but most new commercial installations now use LED exclusively.