The Bulb

The high intensity discharge 600W high pressure sodium (HPS) bulb is a technology used most commonly for street lights and personal indoor horticultural. This system requires a grow tent, grow light materials (HPS bulb, hood, and ballast), and electricity.

For personal indoor horticulture, the bulb is typically mounted in a hood to both expand the light onto the whole plant and absorb extra heat. When plugged into an electrical socket and turned on, the bulb is powered by electrical current that is provided by the ballast and starter. The starter pulses the bulb when turned on to begin the chemical reaction while subsequent voltage comes from the ballast at a much lower level to ensure that the pressure within the arc tub does not continue to climb to an unsustainable level causing the bulb to “cycle” or go out until the pressure falls (Kane and Larson 2001). Voltage is created when alternating current (AC) is transformed into direct current (DC) waves which magnetize the induction coils, generating the required voltage (Ottenstein). These electrons then pass between the two Tungsten electrodes located at either end of the bulb’s arc tube via the gas Xenon. The increased temperature created by the passing electrons heats the Mercury inside of the arc tube, vaporizing it. As the bulb continues to heat, the metallic Sodium inside the arc tube also vaporizes. The interaction of the vaporized Mercury and Sodium gases produce the HPS bulb’s familiar yellow glow, which is considered to be on the white light spectrum (Kane and Larson 2001).