Grower's Choice 315W CMH Grow Light

The GC-315 flowers a 3x3 area effectively and vegs a 3.5x3.5 area. In a 4x4 tent, you'll get solid growth in the center but the corners will be noticeably dimmer. For full 4x4 coverage in flower, most growers either run two 315W fixtures or step up to a 630W CMH or LED. If you're growing one or two large plants in the center of a 4x4, a single 315W can work fine.

LEDs in this price range typically pull similar wattage but produce a narrower, diode-driven spectrum. CMH's advantage is spectral quality: the broad, continuous spectrum is closer to sunlight than the peaked spectrum of most LEDs. Many growers report visibly healthier plants and tighter structure under CMH compared to budget LEDs. The trade-off is that CMH generates more heat and the lamp needs replacement every 15,000 hours. If heat is your main concern, LED may be the better fit. If spectrum quality matters more, CMH wins at this price.

Grower's Choice rates their CMH lamps at 15,000 hours. Running 18 hours per day in veg, that is roughly 2.3 years. Running 12 hours per day in flower, that is about 3.4 years. Spectrum and output do degrade over time, so many growers swap lamps every 12 to 18 months for peak performance. Replacement lamps are available separately on our site.

The ballast accepts both 120V and 240V input. It ships with a 120V plug. To run on 240V, you'll need to swap the plug or hardwire to a 240V circuit. Running on 240V draws less current (1.5A vs 2.9A), which is better if you're running multiple fixtures on the same breaker. The fixture auto-adjusts, no switch or setting needed.

Yes, any standard single-ended 315W CMH lamp with a PGZ18 base will fit. Grower's Choice lamps are optimized for this ballast's frequency and output, so using their lamps ensures the best spectral performance and longest lamp life. Third-party lamps will work but may not perform identically.

Not for a single fixture. A standard appliance timer handles on/off scheduling, and the built-in dial controls dimming. The optional Grower's Choice Master Lighting Controller becomes useful when you're running multiple fixtures and want centralized sunrise/sunset ramping, thermal monitoring, and auto-dim shutdown. We carry the controller separately if you need it later.

If you receive a defective or damaged unit, email us a photo at help@ and we'll make it right immediately: replacement or refund, your call. For change-of-mind returns, we accept returns within 30 days for items in new, resalable condition. If you're not sure whether this product is right for your setup, call us first at 716-217-0353. We'd rather answer your questions before you order.

Happy Hydro has been selling growing equipment since 2006. We've carried Grower's Choice for years because the systems work great and customers who buy them leave happy. Have questions before you order? Call 716-217-0353 or email help@. We're easy to reach and happy to help!