What Are HPS Grow Lights & How Do They Work?
High Pressure Sodium (HPS) grow lights were the industry standard for indoor growing for decades. While LED technology has now surpassed HPS in most metrics, understanding HPS remains valuable—especially if you're currently using this technology or considering your upgrade options.
The Technology Behind HPS Lights
HPS lights are a type of gas-discharge lamp that produces light by creating an electric arc through vaporized sodium under high pressure. This technology creates the characteristic golden-yellow light that HPS bulbs are known for, rich in the red and orange spectrum that flowering plants respond to exceptionally well.
Key Components of an HPS Lighting System
A complete HPS lighting system consists of three main components:
- Bulb: The glass tube containing the sodium vapor, available in various wattages (400W, 600W, 1000W being most common)
- Ballast: Regulates the current to the bulb and provides the initial voltage required to start the arc
- Reflector/Hood: Directs and focuses the light downward onto your plants, often with options for cooling
The HPS Light Spectrum
HPS lights emit light primarily in the yellow, orange, and red portions of the spectrum (550-700nm), making them particularly effective for the flowering stage of plant growth. This spectrum triggers robust flowering responses and encourages dense bud development.
Common HPS Wattages and Their Applications
HPS bulbs come in several standard wattages, each suited to different growing areas:
- 250W: Small grow spaces, supplemental lighting
- 400W: Small to medium grow spaces (2×2 to 3×3 feet)
- 600W: Medium grow spaces (3×3 to 4×4 feet), considered the most efficient wattage
- 1000W: Large grow spaces (4×4 to 5×5 feet and beyond), maximum light output
HPS vs Modern LED: Where We Are in 2024
While HPS served the indoor growing industry well for decades, LED technology has now surpassed it in virtually every metric:
- Efficiency: LED achieves 2.5-3.0 µmol/J vs HPS's 1.0-1.7 µmol/J
- Lifespan: LED lasts 50,000+ hours vs HPS's 10,000-12,000 hours
- Heat: LED produces 70% less heat than HPS
- Spectrum: LED offers full-spectrum light vs HPS's red-heavy spectrum
- Operating Cost: LED saves £400-500+ annually in electricity
Our Recommendation
If you're researching HPS because you're considering what lighting to buy, we recommend looking at LED instead. For the same or slightly higher initial investment, you'll get better efficiency, lower operating costs, and less heat to manage. Check out ourequipment directory for LED recommendations.
When HPS Still Makes Sense
Despite LED's advantages, HPS can still be appropriate if:
- You already own working HPS equipment
- You grow in a cold climate and can use the heat
- You're on an extremely tight budget (used HPS is very affordable)
- You have excellent ventilation and low electricity costs
Did You Know?
HPS lights were originally developed for street lighting in the 1950s and only later adapted for horticultural use. Their efficiency at converting electricity to light made them an ideal choice for growing plants indoors—until LED technology caught up and surpassed them around 2018-2020.