High pressure sodium lamps are in a category of lamps called "high intensity discharge" (HID) lamps which means that they contain mercury and have a high lumen output. Fluorescent light bulbs are known as "energy-efficient bulbs" which means that they also put out high amounts of lumens for the low wattages they require to operate.
The primary function of any type of light bulb is to produce artificial light for a given area. The wattages on light bulbs indicates the amount of power needed to produce a certain amount of lumens. There are several applications for high pressure sodium and fluorescent lamps. High intensity discharge lamps like high pressure sodium lamps are mostly used in outdoor and warehouse settings. Fluorescent lamps are widely used indoors but can also be used outdoors and in warehouse settings.
Lumens are a measurement of the intensity of light output. High pressure sodium lamps as well as fluorescent lamps are designed to put out high levels of lumens per watt. A typical high pressure sodium lamp can put out between 50 and 140 lumens per watt. A typical fluorescent lamp can put out up to 100 lumens per watt.
All high intensity discharge lamps, as well as all fluorescent lamps contain mercury which is know as a dangerous material. Mercury is a recyclable material; used high pressure sodium lamps and fluorescent lamps should be recycled and never thrown away. 250 watt high pressure sodium lamps typically contain around 15 mg of mercury in each lamp. A standard fluorescent tube typically contains around four milligrams of mercury.
Fluorescent bulbs feature a cathode and an anode which are both known as electrodes. They also contain mercury vapor gas and argon. Fluorescent bulbs produce light when a current of electricity is run between the electrodes. Electrons within the bulbs react to the mercury and argon resulting in the production of photons. When these photons contact the inner coating of a fluorescent bulb, light is produced. High pressure sodium lamps contain mercury and sodium. They utilize a ballast and starter to provide a high voltage starting pulse. These lamps usually require between 2,500 and 5,000 volts to start the lamp.
High pressure sodium lamps as well as fluorescent lamps encourage plant growth due to their high levels of lumen output. The orange-red glow produced by high pressure sodium lamps promotes flowering in plants. Fluorescent lamps produce a whiter light than high pressure sodium lamps. This makes fluorescent lamps almost ideal for encouraging seedling and vegetative growth in plants.
High intensity discharge lamps are some of the longest lasting lamps available. Depending on the wattage, high pressure sodium lamps will usually last anywhere from 12,000 to 24,000 hours. Depending on the wattage, fluorescent lamps can last up to 10,000 hours before they need to be replaced.