Ceramic metal halide (CMH) lamps use a ceramic arc tube, like HPS, filled with metal halide salts, like MH. The ceramic tolerates higher temperatures, so the lamp runs hotter and more efficiently with a broader and more stable spectrum than quartz MH. "LEC" (light emitting ceramic) is a marketing name for the same lamp class. The common grow sizes are 315 W and 630 W (two lamps), on low-frequency square-wave ballasts.
In practice
CMH was popular in the 2010s as a single lamp for both veg and flower, valued for its broad spectrum, good colour rendering for inspecting plants and a small amount of UV. Efficacy is roughly 1.5–1.9 µmol/Jbeing reviewed, better than MH and similar to or below DE HPS, and well below modern LEDs.
A 315 W CMH typically covers about 0.9 × 0.9 m (3 × 3 ft) for flower. Like other HID lamps, it emits radiant heat and contains mercury. Some CMH lamps emit enough UV that the fixture glass matters; follow the lamp's rated fixture type.
Don't confuse with
- Metal halide (MH): quartz arc tube, bluer, less efficient.
- HPS: ceramic tube too, but sodium fill and orange-yellow light.
- LED: solid-state; higher efficacy and dimmable over a wide range.
