All About Mercury Vapor Lamps
Before there were metal halide lamps, there was the mercury vapor lamp. In fact, the mercury vapor lamp is the first type of HID (high-intensity discharge) lamp to exist. These lamps offer a number of benefits, including a relatively long lamp life when compared to traditional incandescents, and have been improved over the years to produce the correct color of light. They also have the capability of emitting very clear, intense white light. They have been a popular choice for illuminating outdoor spaces due to the brightness of these bulbs and the fact they provide good night light. This has made them valuable for a number of applications throughout the years, including overhead lighting in big areas like factories and sports arenas. As with metal halide lamps, advancements in lighting technologies have begun to reduce the number of mercury vapor lamps in use. New LED options offer longer-lasting light, energy savings, and a more environmentally-friendly design. Additionally, businesses find these new technologies to be more cost-effective, saving money in the long run. Here at ShineRetrofits.com, we want to make sure our customers have all the information they need to make educated choices about their lighting. To help with that, here’s a look at just what mercury vapor lamps are, how they work, the pros and cons, and some other additional information to help you make the best buying decision.
What is a Mercury Vapor Lamp?
As we previously mentioned, a mercury vapor lamp is an HID lamp. That means that it uses an arc of electrical current that passes through vaporized gases. In this case, it is mercury and it ultimately creates light through arcs. The set-up of a mercury vapor lamp is similar to that of a metal halide lamp. The lamp uses an inner arc tube that is generally made of fused quartz. Fused quartz can go through major temperature changes without cracking, plus it won’t melt at high temperatures. Halide lamps are a great choice for the tube that provides the electrical arc needed to get the lamp to light. The inner arc tube is completely surrounded by an outer bulb, which is generally considered the actual lamp. The outer bulb can be clear, or sometimes coated with a phosphor. The job of the outer bulb is to keep heat in and help lower the amount of ultraviolet (UV) light emitted by the lamp. Plus, today’s mercury vapor lamps are normally under high pressure inside, so the outer bulb keeps everything in and pressure to where it needs to be. When electricity is provided to the mercury vapor lamp, an arc of electrical current passes from an electrode on one end of the inner arc tube to the other. This arc is initiated by a starting electrode. This electrical arc is helped to flow through argon gas inside the bulb between the main electrodes. Once the electrical current starts, the inside of the lamp begins to heat up. This ultimately causes the mercury droplets to vaporize and mix with the argon gas inside. A small arc initiates the lighting process by passing through the argon gas. The mercury ionizes and light emits from the lamp. To help keep the lamp going and make sure it does not use too much electricity, it normally includes a self-ballast with a resistor to regulate the process. Self-ballasted mercury vapor lamps often use a tungsten filament to limit the current and aid in ignition.
History of the Mercury Vapor Lamp
The history of the mercury vapor lamp goes all the way back to 1835, when an English inventor and scientist by the name of Charles Wheatstone first started experimenting with what would happen when an arc of electricity was passed through mercury vapor. His experiments produced different colors being emitted depending when a prism was introduced into the mix. Then a few years later in 1860 another Englishman, John Thomas Way, developed a very primitive version of the mercury vapor lamp. Later in 1892 Leo Arons of the University of Berlin also came up with an early version of the lamp. However, Arons lamp emitted light that had too much of a bluish-green tinge. It wasn’t until 1901 that a version of the mercury vapor lamp we know of today is an invention of American electrical engineer Peter Cooper Hewitt. On September 17, 1901, Hewitt received a US patent for his invention. Then two years later, Hewitt developed an upgraded version of his mercury vapor lamp that offered better light color quality. One drawback of Hewitt’s original mercury vapor lamp was the large amount of mercury that the lamp needs. In the 1930s, researchers worked to see if they could still use the same process, just with less mercury required. These newer lamps were ultimately made by companies such as General Electric.
Principle of Operation
The principle of operation of a mercury vapor lamp revolves around creating an electric arc through vaporized mercury to produce light. At the heart of this process is a small fused quartz arc tube filled with a mixture of mercury vapor and an inert gas, such as argon or nitrogen. When an electric current passes through the arc tube, the mercury vapor ionizes, resulting in a bright light through a process known as electroluminescence. This light is emitted through the outer bulb, which can be clear or coated with a phosphor to enhance color rendering. The mercury vapor lamp ballast is crucial in this setup, as it limits the current to prevent the arc from becoming too strong, ensuring efficient and safe operation.
Mercury Vapor Lamp Pros
Energy Efficiency -- Compared to incandescent bulbs and some fluorescent lights, mercury vapor lamps consume less energy and offer higher luminous efficacy. This means they provide more light output per watt of power consumed, making them a more economical choice for lighting large spaces over extended periods.
Bright White Light -- Mercury vapor lamps are well-known for producing a crisp, clean white light, which stands out compared to older lighting technologies. This bright illumination enhances visibility and safety in outdoor and industrial environments, making them ideal for street lighting, parking lots, and sports arenas.
Long Lamp Life -- Mercury vapor lamps typically last at least 24,000 hours, with many exceeding this lifespan. This durability makes them an excellent choice for hard-to-reach fixtures found in locations such as factories, sports arenas, and street lighting installations. The extended lifespan reduces maintenance costs and the frequency of lamp replacements, contributing to overall cost savings for businesses and municipalities.
Compatibility -- Mercury vapor lamps are compatible with various mercury vapor fixtures designed specifically to optimize their performance and safety. The use of liquid mercury inside the arc tube allows the lamp to produce a stable and intense light output once the lamp reaches operating temperature. Although these lamps require a warm-up period, their steady and reliable illumination has made them a trusted lighting technology for over a century.
Environmental Resilience -- Mercury vapor lamps also tend to perform well in different environmental conditions, including colder temperatures where some other lighting technologies may struggle. Their robust manufacturing and design contribute to their resilience and consistent operation in outdoor lighting purposes, helping to ensure well-lit areas regardless of weather conditions.
Mercury Vapor Lamp Cons
Phasing Out – One of the biggest drawbacks of mercury vapor lamps is that they are being phased out in the United States. The Energy Policy Act of 2005 specifically banned the use of mercury vapor ballasts, signaling a shift away from this lighting technology.
Blue-Green Light – Mercury vapor lamps often emit a distinct blue-green light due to the materials involved in their light production. This color tint can make them less appealing for retail and indoor environments, as it can distort the appearance of human skin and other colors.
Warm Up Time – These lamps require a warm-up period ranging from four to seven minutes before reaching full brightness, which can be inconvenient in some settings.
Mercury Content and Disposal – Containing mercury, these lamps raise environmental and health concerns. Proper disposal is essential, and the US Environmental Protection Agency (EPA) has established guidelines for safely discarding used mercury vapor lamps. When handled and disposed of correctly, they pose minimal risk to users.
UV Radiation – Another cause for concern is the fact that mercury vapor lamps can become exceedingly hot during use, which poses safety concerns. Although the outer bulb helps to keep much of the radiation away from the end user, if the outer bulb was to break and the inner arc tube kept emitting light, the amount of UV radiation could potentially cause serious health risks for those exposed to it. The outer bulb can be clear, or sometimes coated with a phosphor, which ensures that UV rays are blocked effectively.
Applications of Mercury Vapor Lamps
Mercury vapor lamps have been widely used for various applications, including street lighting, factories, and large areas such as parking lots and warehouses. They are also popular in high-ceiling buildings, gyms, and other spaces requiring high-intensity lighting. Additionally, low-pressure lamps with a quartz envelope are utilized for germicidal purposes, such as water treatment and air purification. Mercury vapor lamps find use in medical applications due to their germicidal properties and in niche markets like moth attracting and insect trapping. Their high-intensity light output and long lifespan make them a preferred choice for these applications, despite the availability of more energy-efficient options like LED lighting.
Environmental Impact of Vapor Lamp
The environmental impact is a significant concern due to the presence of mercury, a toxic substance that can harm humans and the environment. The production and disposal of mercury vapor lamps can lead to mercury pollution, contaminating soil, water, and air. Additionally, the energy consumption of these lamps contributes to greenhouse gas emissions and climate change. However, many manufacturers are now adopting more environmentally friendly materials and production processes to minimize the environmental impact. Regulations and laws are also in place to limit the use and disposal of mercury-containing products, including mercury vapor lamps.
Retrofitting Mercury Vapor Lamps
You can retrofit HID fixtures with kits like this one from Encore LED. So how do mercury vapor lamps measure up when compared to newer technologies, such as fluorescent/CFLs and LEDs? For the most part, our customers look for retrofitting options to replace mercury vapor lamps. They want newer lighting options that offer savings when it comes to energy, labor and maintenance. Ultimately the lighting choice you decide upon will be the best fit for your needs. Here at ShineRetrofits.com, we just want to make sure our customers have all the information they need. This helps them to make well-educated decisions. Here's a look at how mercury vapor lamps measure up to both fluorescent/CFLs and LEDs.
Mercury Vapor Lamp vs. Fluorescent/CFL
As we have already mentioned, mercury vapor lamps offer a lot of great advantages -- vivid light and long lamp life -- which has given them the nickname of "the workhorse" of lighting, making them great choices for places that need reliable lighting such as streetlights and sports arenas. When compared to fluorescents and CFLs, these newer technologies do have major drawbacks when it comes to surrounding ambient temperature as they have a hard time operating in very cold areas, making them potentially not as great an option as mercury vapor lamps for outdoor applications. On the flip side, fluorescents and CFLs do have certain characteristics that help make up for some of the disadvantages with mercury vapor lamps. For instance, fluorescents take much less time to heat up and emit light. Plus they offer even longer lamp life and greater energy efficiency. It's important to note that switching to a fluorescent lighting solution does not do away with mercury. They still contain a small amount, and as such have their own disposal rules and regulations.
Mercury Vapor Lamp vs. LEDs
When compared to LEDs, the major advantage that mercury vapor lamps offer is cost. Although the cost of LEDs continues to drop, they are still much more expensive up front. They can sometimes be cost-prohibitive for contractors to fully use in a project. Another potential disadvantage to LEDs is the fact that there really is no such thing as "white" LED light. White light is created through the use of multiple colors of LEDs, which is something mercury vapor lamps don't do. However, an advantage of LEDs is the fact they are available in such a variety of colors. They are ideal for use in areas -- like retail -- that mercury vapor lamps usually are not. Other advantages LEDs offer are an even longer light life, better energy efficiency, and the fact they contain no mercury. This makes them environmentally friendly.
The Future of Vapor Lamp Technology
The future of vapor lamp technology is uncertain as more energy-efficient and environmentally friendly options like LED lighting gain popularity. However, mercury vapor lamps will likely continue to be used in certain niche applications where their high-intensity light output and long lifespan are beneficial. Researchers are exploring new technologies, such as UV-light LEDs, which could potentially replace mercury vapor lamps in industrial applications. As lighting technology evolves, we can expect more efficient and sustainable options to emerge, eventually phasing out the use of mercury vapor lamps. The development of new technologies and the improvement of existing ones will depend on factors like cost, efficiency, environmental impact, consumer demand, and regulatory frameworks.
Originally published September 2016. Updated May 2025 with new content