Metal Halide or High Pressure Sodium?

Technically, either one will do the job, however when both are used correctly they will produce superior results. Let's take a look at some specs for both setups:


Metal Halide:

• Spectrum: Usually between 4000-5400k (Blue)
• CRI: 65-90nm (Cool-Full Spectrum)
• Wattage: Most are between 175-1000W
• Heat Generated: Medium-High
• Lumens: 65-115 per/watt (Depending on Bulb)
• Average Lifespan: 20,000 Hours

High Pressure Sodium:

• Spectrum: Usually between 2000-2400k (Red)
• CRI: 20-25nm (Warm Spectrum)
• Wattage: Most are between 150-1000W
• Heat Generated: High
• Lumens: 50-145 per/watt
• Average Lifespan: 25,000 Hours

Let's take a look at what plants need during their main 2 cycles:

Vegetative:

• Spectrum: Cool Blue-Full-Daylight Blue (4500-6500k)
• Wattage to Lumen Penetration: Minimum of 35 lumens per/watt, 100+ Preferred
• Heat Tolerance: Up to 89F max, however stress will begin at this temperature
• Lifespan: Average of 6 Weeks minimum, or 756 Hours of 18/6 Spring/Summer Cycle
• Best Choice of Lighting: Metal Halide @ 50-100W per plant or higher for better results.

Flowering

• Spectrum: Autumn/Winter Warm Red/Orange (2000-2800)
• Wattage to Lumen Penetration: Minimum of 50 lumens per/watt, 100+ Preferred
• Heat Tolerance: Up to 85F max, however stress will begin at this temperature
• Lifespan: Average of 6 weeks minimum, or 504 Hours of 12/12 Photoperiod 
• Best Choice of Lighting: High Pressure Sodium @ 100-200W per plant or higher

Kelvins Spectrum

Conclusion:

For best results and highest yields, use MH lights for the Vegetative Cycle, and HPS lights for the Flowering Cycle. This will ensure that the plants are receiving the proper spectrum during the designated cycle given. MH lights will mimic the Spring/Summer sun, and you will leave them on for a minimum of 16-18 hours a day to simulate the longer days when the planet is closer to the sun. HPS lights will mimic the transition as to when the planet is revolving away from the sun bringing forth the end of Summer and the beginning of Autumn. You will simulate these shorter days by only leaving your HPS light on for 10-12 hours a day. 

Running Costs:

Electric companies usually charge by the kilowatt hour(kWh). What this means is for every 1000W of total energy being drawn for an hour, they will charge a specific price. So for example, if you have a 1000W HPS light running at a 12/12 cycle, and your electric company charges $0.23/kWh, then your cost would be $2.76/day or roughly $82.80/mo.

400W MH/HPS @ $0.23/kWh: 20/4: $55.20/mo. 18/6: $49.80/mo. 12/12: $23.00/mo.

600W MH/HPS @ $0.23/kWh: 20/4: $82.80/mo. 18/6: $74.40/mo. 12/12: $49.80/mo.