The three common types
Most home growers choose between LED and HID (HPS or CMH). For a first grow, LED is the most straightforward.
- LED: efficient, low-heat, no bulbs to replace, higher upfront cost. The usual recommendation.
- HPS: cheaper upfront with proven yields, but hot and power-hungry, and it needs more cooling.
- CMH / LEC: strong spectrum and a middle ground, with bulbs that last a year or two.
How much light you need
Work in actual-draw watts per square foot rather than the 'equivalent' numbers on the box. A useful target is 30 to 40W of actual draw per square foot of canopy.
- 2×2 (4 sq ft): about 120 to 150W
- 2×4 (8 sq ft): about 240 to 320W
- 4×4 (16 sq ft): about 480 to 640W
Light schedule
Photoperiod plants switch between growth and flower by the light timer, not by age. Run 18 hours on for vegetative growth, then change to 12 on and 12 off to start flowering. Autoflowers don't respond to this, and many growers run them on a long schedule such as 18/6 or 20/4 from start to finish.
Hang height
Too close can bleach or burn the tops; too far lets plants stretch and reduces yield. Follow your light's chart, then read the plant: tight new growth and slightly cupped ("tacoing") leaves suggest raising or dimming the light. As a quick check, hold the back of your hand at canopy height; if it feels uncomfortably hot, the light is too close.