315 Watt CMH & LEC Grow Lights
The 315W CMH (ceramic metal halide) is the most widely used single-lamp CMH configuration in indoor growing -- a complete one-fixture setup for a 3x3 ft canopy that delivers the CMH format's signature full-spectrum output including UV, at 1.9+ umol/joule efficiency in a compact, practical wattage. The 315W class represents the sweet spot of the CMH format: meaningful UV and full-spectrum output without the electrical load of a 630W double-lamp unit, and more complete spectrum quality than standard MH or HPS at equivalent wattage.
315W CMH for 3x3 Canopy Coverage
A quality 315W CMH fixture with an appropriate reflector covers a 3x3 ft canopy at adequate vegetative and moderate flowering PPFD levels. At 1.9-2.0 umol/joule, a 315W CMH produces approximately 600-640 umol/s of total output -- delivering 700-800 umol/m2/s across a 3x3 canopy at standard hanging height, which is productive for flowering for most crop types though not at the peak intensity of higher-wattage options. Growers who run 315W CMH typically prioritize spectrum quality and UV benefits over maximum PPFD, particularly for specialty crops where secondary metabolite production and product quality metrics are primary considerations. For a 4x4 ft canopy at flowering intensity, the 630W CMH (double-lamp unit) is the appropriate size step-up. See our updated grow light bulb types guide for a full CMH format overview.
315W CMH Brands & Bulbs
Philips MasterColor CDM 315W is the category benchmark -- the original commercial-grade 315W CMH bulb with the highest output and most consistent quality in the class. Gavita, Phantom, and Iluminar produce complete 315W CMH fixture systems (ballast, reflector, and lamp) ready for installation. All 315W CMH fixtures require a dedicated CMH-rated ballast -- compatible replacement Philips CDM bulbs are also available here. -- not compatible with standard MH or HPS ballasts. Expert support available.
315W CMH FAQ
What is the difference between 315W CMH and 630W CMH?
The 315W CMH uses a single ceramic arc tube lamp and covers a 3x3 ft canopy. The 630W CMH uses two 315W lamps in a single fixture housing and covers a 4x4 ft canopy at double the photon output. A 630W CMH unit is not simply a different ballast -- it is a physically larger fixture designed to house two lamps with individual reflectors that together cover the larger footprint. For a dedicated 3x3 ft setup, the 315W is the right size; for 4x4 ft coverage at CMH quality and spectrum, the 630W is the appropriate choice.
Can I use a 315W CMH as my only grow light?
Yes, for a 3x3 ft canopy. A 315W CMH provides adequate PPFD for both vegetative growth and moderate-intensity flowering across a 3x3 ft footprint. For maximum flowering intensity in a 3x3, a 400W LED at 2.7+ umol/joule produces higher total PPFD at the same wattage due to LED's higher efficiency -- but the CMH's full-spectrum UV output provides quality benefits the LED may not match. For growers who prioritize spectrum quality and UV secondary metabolite benefits over maximum PPFD, the 315W CMH is a well-justified single-fixture choice for a 3x3 tent.
