Streetlights and industrial lights, such as those found in parking garages or manufacturing facilities, give off a yellowish or orange glow because they are sodium vapor gas-discharge lights. There are two types of sodium vapor lights, high pressure (HPS) and low pressure (LPS). Today in places where sodium vapor lights are still used, high-pressure sodium lights more common as they are more energy efficient than the low-pressure version.
Low-pressure sodium lights give off a yellow or orange glow because they only produce a single wavelength of yellow light, which results in a less intense light output. The glass bulb houses solid sodium metal that vaporizes once the light is turned on. It is during the start of the light turning on, while the sodium is still solid in form, that the light emits that dim reddish-orange glow. While these low-pressure, monochromatic lights have the worst color rendering out of any other light on the market today and interferes with color vision at night, they are still used under bridges, inside tunnels and in streetlights.
High-pressure sodium lights are widely used in industrial settings such as manufacturing plants, parking lots and in security areas as well as in streetlights. This type of sodium vapor light produces a wider spectrum of light than the low-pressure version, making it brighter and less orange in color. High-pressure sodium lights still give off a yellowish glow, but the Mercury inside the light helps counter-balance that yellow glow with a small amount of white or light blue color emission.
Brief History of Sodium Vapor Lights
These sodium vapor lights were invented in the mid-20th century with commercial production starting in the 1930s and become more common in the late 1980s because of their efficiency in lighting large areas. Since sodium lights produce light in a range on the electromagnetic spectrum that is extremely sensitive to the human eye, there is less power required to light large areas like streets, parking garages and parking lots. Energy efficiency is the reason they have been so widely used.
Today however, LED (light-emitting diode) lights are being used more commonly as they are even more energy-efficient, cost-effective and have a much longer lifespan. The trade-off though, is that the light output of an LED is much brighter and bluer in color, which can disturb people’s sleep when used in streetlights. LED lights give off white color emissions because they produce light on the white and blue portions of the electromagnetic spectrum around 5,000K.
Larson Electronics carries a wide variety of lights for personal or commercial use, including explosion proof lighting, GoLights, LED lights, spotlights, searchlights and more that range in intensity, brightness, color temperature and application.