U-M Guide to Energy-Efficient Lighting
Green Lighting, a Bright Idea!
Lighting consumes a greater share of U-M’s energy budget than any other function except heating. Each year over $4 million is spent on electricity to operate the lights in the buildings on U-M’s Central and North campuses in Ann Arbor.
Inefficient lighting (in addition to unnecessary energy costs) also has a negative impact on the environment by requiring the combustion of greater quantities of fossil fuels in electric power plants. The burning of coal, oil, or natural gas results in atmospheric pollutants shown to cause acid rain, smog, and global warming. Lighting is a prime opportunity for cost saving. Not only can the right lighting system lower electricity bills, but it can often make a work environment more comfortable.
On this page you will find information about lighting systems and the ways they can be made more efficient. Hopefully, with everyone's cooperation, we can transform the U-M campus into an example of efficient and environmentally friendly lighting.
Here is a quick overview of the major lamp technologies in use at the University of Michigan and their typical uses.
As a general rule, U-M uses fluorescent light fixtures to provide illumination in most of its buildings. Fluorescent lighting has been shown to be the most efficient and cost-effective lighting for high-quality illumination suitable for most classrooms, offices, and laboratories.
Linear Fluorescent Lamps
Fluorescent lamps come in many different ratings. There is a great deal of confusion about what the ratings mean, and which rating is best for a given application. Hopefully, the following discussion will clear up most of the confusion.
The older, less-efficient fluorescent lamps were designated as “T-12” lamps, meaning simply that the diameter of the bulb was 1.5 inches. Under Federal regulations adopted in 1992 as part of the Federal Energy Act of 1992, no T-12 lamps were to be manufactured after October 1995.
T-8 lamps, having a tube diameter of 1.0 inch, are more efficient and are used in place of the old T-12s. T-8 lamps are rated at 32 watts compared to the 40 watt rating of T-12 lamps, and yet they provide the same amount of illumination.
Many people are concerned about whether the “color” produced by the newer fluorescent lamps is as good as what they have become used to. The ability of lamps to render colors is rated by illumination engineers by a Color Rendering Index (CRI). Under the CRI, a light source with a rating of 100 has the same color rendering qualities as sunlight.
The old T-12 fluorescent lamps had a CRI rating of about 62; the light that they produced, while intense, did not have the characteristics of sunlight. That is why you often heard people complaining about the “artificial,” or “unnatural” feeling of a room illuminated by the old fluorescent lamps.
The T-8 lamp which the University has adopted as its new standard has a CRI of 75, which is a 21 per cent improvement over the old T-12s. This means that colors should appear truer to sunlight under the T-8 lamps.
Note: Fluorescent lamps are available which have CRI ratings as high as 90, however, the lumen efficiency may be less. In addition, the higher the CRI rating, the more expensive the lamp. In rare applications which require excellent color rendering it may be necessary to install a lamp having a CRI of 85 or higher.
The chromaticity of a fluorescent lamp is another parameter used to gauge light quality. Chromaticity refers to the pattern of visible wavelengths emitted by a bulb. Chromaticity is measured in units of degrees Kelvin (K).
Most lamps fall in the range of 2200 to 7500 K. The lower a lamp’s Kelvin rating the more it will create a visually “warm” atmosphere, with a slightly pinkish coloration. Many people prefer to use these “warm white” lamps in their homes, because they create coloration which is psychologically warm and restful.
The higher a lamp is rated on the Kelvin scale the “cooler” it will appear, creating bluish tones that some people find harsh or uncomplimentary.
The T-8 lamp which the University has adopted as its standard has a chromaticity of 3500 K. These lamps are considered to be visually “neutral,” being neither warm nor cool, and result in improved color rendering for most general office work.
“Full Spectrum” Lamps:
“Full spectrum” lamps are defined as fluorescent lamps having a CRI of 90 or better and a color temperature of 5000 K. They are designed to provide a completely balanced pattern of visible wavelengths for applications where highly accurate color rendering is required. In a sense, full spectrum lamps produce the most accurate colors, however they are not “natural” in the sense that they do not replicate natural sunlight, or the normal conditions in which people view things. Full spectrum lamps are much more costly than regular lamps, and they require more electricity for a given level of light output.
The T-8, 3500 K fluorescent lamp was designated as the U-M “standard” in 1993 based upon its improved performance and energy efficiency. The T-8 lamp provides a high quality of light which is suitable for the vast majority of functions carried out in U-M buildings. In most cases, the new T-8 lamp will provide a higher quality of illumination than the T-12 lamps which they replace, in the sense that colors will be truer and closer to natural daylight.
In a few rare instances, certain areas that carry out special functions may require a lamp having different characteristics than the standard T-8. Please contact your Facilities Manager or the lighting engineers in the Utilities Department to discuss these situations and the options which are available.
Compact Fluorescent Lamps
Many offices and work areas are equipped with small incandescent lamps. But it’s worthwhile to replace these fixtures with compact fluorescent lamps (CFL) where possible.
You see compact fluorescent lamps in every hotel room these days. A CFL provides the benefits of fluorescent illumination in a device that can be installed into the screw-in sockets used in your household lighting fixtures.
Compact fluorescent lamps can use 75% less energy and can last more than ten times longer than incandescent (tungsten filament) lamps. For example, a 26- watt CFL lamp can replace a 100-watt incandescent lamp while providing the same light level. It may surprise you to find that CFLs are readily available in a variety of color temperatures, and if you’re looking for a warm lamp by which to read your favorite book, you’ll find a CFL to meet your need.
When compared to conventional incandescent lamps, tungsten halogen lamps offer longer life, higher efficiency, and more compact size. They are, however, more expensive than conventional lamps. Because of these characteristics, they are used in applications such as floodlighting, display and accent lighting, and automobile headlights.
Even more efficient than regular halogen lamps are Halogen-IR (HIR) lamps. These lamps trap wasted invisible infrared emissions and redirect them to produce more visible light. This results in a more than 40% efficiency gain over standard halogens, while providing the same amount of light output, beam control, and compactness as the standard halogen.
High Intensity Discharge (HID)
These discharge lamps use ballasts to produce light by passing an electric current through a vapor or gas like the fluorescent lamps, rather than through a tungsten wire. HID lamps are some of the most efficient and long-lived lamps available. They have a long lamp life (approximately 10,000–25,000 hours) and high light output, and can cover large areas. This makes them a good choice for industrial, commercial, and floodlighting applications.
The majority of HID lamps are either metal halide (MH) or high-pressure sodium (HPS). MH lamps provide a white color while HPS lamps offer a yellow-orange hue. These lamps can be used for street or parking lot lighting and industrial and commercial applications such as gyms and rooms with high ceilings, as well as retail merchandise displays. Some models can also be used in office or classroom applications.
No lighting discussion would be complete without mentioning the device that keeps many bulbs lit—the ballast. Fluorescent and HID lamps both create electrical arcs within various gases to produce light. The ballast is a device mounted inside a lighting fixture which develops the proper voltage needed to start the flow of electricity through the gas, and regulates the current flow to stabilize the light output.
In the past, the most common and inexpensive type of ballast was an electromagnetic design which operated at 60 Hertz with a heavy transformer. Electromagnetic ballasts have several drawbacks, including noise, light flicker, heat, and most importantly inefficiency.
Electronic ballasts, while costlier than their older electromagnetic siblings, have several benefits that make them preferable on several fronts. Lamp manufacturers have developed a ballast of electronic design which is rapidly replacing the older electromagnetic types in most buildings in the U.S. These electronic ballasts operate at frequencies much higher than 60 Hz; in fact the typical electronic ballast operates at above 20,000 Hz. This high-frequency operation eliminates the annoying problems of light flicker and noise which have been the bane of fluorescent fixtures.
Because of their obvious advantages, the University of Michigan has made a commitment to replacing worn-out electromagnetic ballasts with electronic types. For several years, Plant electricians have followed the practice of installing electronic ballast whenever an electromagnetic ballast fails. The clear advantage of electronic ballasts has led to the decision in some buildings to make a complete changeover all at once, even though the existing electromagnetic ballasts may still be functioning. The energy cost savings from such a change are often large enough to justify this approach. In addition, the quality of lighting is usually improved.
Hybrid solar lighting is a new substitute for skylights with several possible advantages. With the aid of a solar dish on a building roof, sunlight is “piped” via optical fiber to your desired room. This allows you to have directional light, avoid the thermal and security concerns of a skylight, and get the visual benefits of full-spectrum light from the sun (sans UV and infrared). The Sunlight Direct website has more information and working prototypes.
LED, or Light Emitting Diode, is another exciting technology that is showing a lot of potential. While LEDs themselves have been around for years illuminating your remotes, displays, and electronics, advances have increased their brightness and commercial viability in general lighting applications. There are still cost disadvantages to hurdle, but commercial products are starting to appear and their life-span and efficacy (lumens or light-output per watt) are growing.
Another way to save energy on lighting is by ensuring that lights are only used when they are needed, or only to the extent they are needed. An occupancy sensor is a device that detects the presence of people in a room and turns off the lights when the room has been unoccupied for a set period of time. When a sensor detects someone entering the room it will turn on the lights again. There are several different types of sensors; some operate by detecting the heat emitted by a person’s body, and others by sensing movement using ultrasonic Doppler technology. Adjustable time delays are incorporated to the specific needs of the area being served. With an occupancy sensor, you can expect an average energy savings of:
If it is not practical to turn off all the lights in a room, it may be worthwhile to install lighting systems that have dimming capabilities. These allow the reduction of the lighting intensity in a room during periods of non-occupancy. In addition, they are sometimes used to adjust lighting in response to changes in the amount of natural daylight. It is important to remember that not all lamps work with dimming circuits (many compact fluorescents, for example, do not). To get this capability, it may be necessary to replace both the lighting fixtures and the lamps.
What You Can Do
Many of the things that are being done to improve lighting efficiency at U-M involve the overall design and layout of the lighting system. Once a lighting system is in place, however, there are a number of things that building occupants can do to reduce the energy used for lighting:
We hope this has been helpful in answering some of the questions that are most often asked about lighting systems and lighting system retrofits at the University of Michigan. Trying to reduce energy costs should be a concern to all members of the U-M community. If we conserve energy we save money, all the while practicing responsible stewardship of the planet.
Content modified: August, 2007