In an effort to provide educational material to the lighting community, we continually strive to support the many generations of lighting engineers. We know many lighting professionals with years of experience may be very astute in some of the topics we offer. However, the audience is shifting. Many younger engineers having multi-disciplinary educations are eager to further their knowledge in lighting design, engineering and specification development.
Mercury vapor lamps were the first high intensity discharge lamps to be commercially available for a wide variety of lighting applications. Most models produce a bluish-white light. Mercury vapor lamps are gas discharge lamps that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger glass bulb. The advantage is that it produces a bright white light, with relatively long life. The outer bulb may be clear or coated with a phosphor. Mercury lamps are available in medium and mogul base versions; and while most wattages require a ballast to operate, some have an internal start that does not require a ballast (often referred to as “self-ballasted” mercury).
Historically, the advantages of Mercury vapor lamps is that they are more energy efficient than incandescent and most fluorescent lights, especially for outdoor applications, with luminous efficacies of 35 to 65 lumens/watt. In addition, their long bulb life (in the range of 24,000 hours), along with a high intensity, clear white light output has made them ideal for outdoor use such as landscaping and street lighting applications spanning many decades. Clear mercury lamps produce white light with a bluish-green tint due to the chemicals used within the arc tube, which is mostly mercury. Because of this, mercury lamps are not suited to render human skin color well, so such lamps are typically not used in retail stores, schools, hospitals and other similar commercial applications. Conversely, in landscaping applications, they make plants and trees look extremely rich and vibrant, as they bring out the green color of foliage beautifully. In recent years, the advent of color corrected mercury bulbs helped improve the problem of color rendering using a phosphor on the inside of the outer bulb that emits better white light. This phosphor technology offers better color rendition than the more efficient, high or low-pressure sodium vapor lamps, but still falls short of metal halide and ceramic metal halide sources.
While many applications are ideal for Mercury vapor lamps, they are being challenged by the higher efficiency and better color balance of metal halide and ceramic metal halide lamps, and LED technologies.
As in any lighting design, typical lighting design considerations for mercury lamps should include, first and always, the application. Determine required and desired light levels, energy efficiency requirements, intensity and clarity of light, length of life and costs.
Conclusion
Mercury vapor lamps have been used in lighting applications, from streets and parking lots, to landscape lighting, to factories and gymnasiums since the 1940’s. They are more energy efficient than incandescent lamps and have a much longer life. The disadvantage is they do not flatter the human skin color thereby making them not an ideal technology for indoor applications. They are exceptional sources, though, for landscape lighting applications.
Thanks for sharing this. I would like to add few to your list.
1. Ecologically Friendly – LED Lighting Is Much More Eco-Friendly
LED lights are free of toxic chemicals. Most conventional fluorescent lighting bulbs contain a multitude of materials like e.g mercury that are dangerous for the environment.
LED lights contain no toxic materials and are 100% recyclable, and will help you to reduce your carbon footprint by up to a third. The long operational life time span mentioned above means also that one LED light bulb can save material and production of 25 incandescent light bulbs. A big step towards a greener future!
2. Durable Quality – LED Illumination Can Withstand Rough Conditions
LEDs are extremely durable and built with sturdy components that are highly rugged and can withstand even the roughest conditions.
Because LED lights are resistant to shock, vibrations and external impacts, they make great outdoor lighting systems for rough conditions and exposure to weather, wind, rain or even external vandalism, traffic related public exposure and construction or manufacturing sites.
3. Zero UV Emissions – LED Lighting Features Close to No UV Emissions
LED illumination produces little infrared light and close to no UV emissions.
Because of this, LED lighting is highly suitable not only for goods and materials that are sensitive to heat due to the benefit of little radiated heat emission, but also for illumination of UV sensitive objects or materials such a in museums, art galleries, archeological sites etc.
4. Operational in Extremely Cold or Hot Temperatures
LED are ideal for operation under cold and low outdoor temperature settings. For fluorescent lamps, low temperatures may affect operation and present a challenge, but LED illumination operates well also in cold settings, such as for outdoor winter settings, freezer rooms etc.
5. Low-Voltage – LED Lighting Can Run on Low-Voltage Power Supply
A low-voltage power supply is sufficient for LED illumination. This makes it easy to use LED lighting also in outdoor settings, by connecting an external solar-energy source and is a big advantage when it comes to using LED technology in remote or rural areas.