Indoor Cannabis Growing Guide: Lighting Fundamentals (Part 1)

Successful indoor cannabis cultivation replicates—or improves upon—natural growing conditions. Light is the single most critical factor. This guide covers the three essential lighting technologies for each growth phase.

Phase 1: Seedlings & Clones (Weeks 1–3)

Fluorescent T5/T8 tubes (LSR) — High blue/white spectrum promotes stem and leaf development. Energy-efficient, low heat—can hang inches above canopy. Run 18/6 light/dark cycle via timer.

Phase 2: Vegetative Growth (Post-20cm Height)

Plants need higher intensity. Two primary options:

• Metal Halide (MHL): High blue output, intense lumens. Ideal for vegetative vigor and mother plants.
• High-Pressure Sodium (HPS/NDL): Red-heavy spectrum. Usable for veg but less efficient than MH. However, HPS works for BOTH veg and flower—making it the single most versatile lamp.

Phase 3: Flowering

Switch to 12/12 light/dark cycle. HPS (NDL) excels here—high red output drives bud development. Highest lumen-per-watt efficiency of all options.

Sample Lighting Schedule

1. Weeks 1–3: T5 fluorescent, 18/6, close to canopy
2. ~20cm height: Switch to MH, maintain 18/6 until target height
3. Pre-flower stretch: Plants may double/triple in height—plan headroom
4. Flower trigger: Switch to HPS, 12/12 cycle
5. Flower duration: 5–12 weeks depending on strain

Pro Tip

Combine all three lamp types for a complete, optimized system. T5 for starts, MH for veg structure, HPS for flower yield. Quality ballasts, reflectors, and ventilation complete the setup.

Keep it Green.