High-pressure sodium lights are a good choice because they emit a light that is stronger in the orange / red spectrum, due to their rich sodium content. Growing a young plant with HPS bulbs will ensure an impressive vertical growth.
Not only is this a great grow light during the flowering stage, but it has two features that make it a more economical choice.
Their average lifespan of high-pressure sodium lights is twice that of metal halides. Still, after 18,000 hours of use (around 12 to 18 months), they will start to consume a bit more electricity than their rated watts and these HPS lights will gradually produce less light because they will require more energy to maintain the gas inside.
HPS bulbs are considered very efficient because they produce up to 140 lumens per watt.
High-pressure sodium lights operate and emit light when an electrical current flows through the ionized gas or plasma. Usually, they require some time to heat up and an electronic system known as ballast is required to play the role of a resistor. The ballast’s role is to regulate the electrical current flow through the entire circuit. When the ballast cannot supply enough voltage it will begin to shut down as the pressure of the tube reduces. This is how you know it’s high time you go to the local store and get a new bulb.
HPS grow lights emit a lot of heat. Imagine a 1,000-watt heater in your room during a cold winter night. The high-pressure sodium lights produce similar heat. The HPS grow light heat is radiant and directed straight onto your plants. This means that you need to create a large gap between your lights and the plants.
A smaller wattage system (between 100 W and 250 W) should be hung at about 2 or 3 feet from the tip of the plants. Medium wattage systems (ranging from 400 W to 600 W) should be hung at about 4 feet from the top extremity of the plants. And high wattage systems (more than 1000 W) should be placed roughly at around 4 to 6 feet higher than the plant. It is recommended that you also look into getting a cooling system of your grow room operation.
One thing high-pressure sodium lights are not very good is when it comes to the growth phase of plants. Yet for the flowering phase, they are by far the best as they are deficient in the blue spectrum. Your best bet is to use a Metal Halide light for vegetative growth and then high-pressure sodium lights for the flowering stage.