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Ten Factors to Consider when Planning a Lighting Retrofit

By Jack Ries
Director, Product Innovation

Many schools are removing the aged fluorescent systems installed in classrooms and offices and replacing them with more technologically advanced systems. Often the motivation for a retrofit is reduced operating and energy costs. However, schools are also reaping the benefits of higher quality illumination.

At Northwood Middle School in Fort Wayne, Indiana, for example, retrofitting an existing fluorescent system boosted light levels to 50 footcandles in classrooms. Replacing an aging fluorescent system in the library of Holy Spirit Catholic School in Tuscaloosa, Alabama, increased horizontal footcandle levels by 34 percent. Vertical footcandles were also increased by more than 25 percent.

To gain the best results from a lighting retrofit, below are seven factors to consider during the design process:

Project Goals

One of the first questions to ask during the planning stage of a retrofit project is what is the objective? What is the existing lighting system, and why do you want to replace it? What do you hope to gain with a new system?

In many instances, schools will benefit from technological advances or energy savings that create “opportunity costs.” Schools that installed systems with T-12 fluorescent lamps and magnetic ballasts during the 1950s and ‘60s have found the systems are not only inefficient but costly to operate. The trend is to replace these systems with the more efficient T-8 lamps and electronic ballasts.

In the library at Holy Spirit Catholic School, 15 4-foot fluorescent fixtures with three T-8 lamps and electronic ballasts replaced 12 8-foot units with two T-12 lamps and magnetic ballasts. According to Phil Onstott, owner of ProElectric, Tuscaloosa, who led the lighting project, the new system increased light levels and reduced energy and maintenance costs.

The existing system with the T-12 lamps required 1.92 kilowatts, compared to 1.3 kilowatts for the new system. Lamp life for the T-8 lamps is 20,000 hours, compared to 12,000 hours for the T-12 lamps. With the original system, ballast temperature was 180 degrees. Now, it is 85 degrees.

“The previous system generated a lot of heat on the ceiling, which escalated air conditioning costs. Much less cooling is needed now, which saves the school money,” Onstott described.

Tasks Involved

The next question is how is the facility used? Are students involved in the learning process within this space?

Today, many students are utilizing computers within the classroom. Screens can be difficult to see if the lighting fixtures are producing a high level of brightness, or if the light is provided directly from one source.

Whether students are working on computers, writing on desktops, or reading the blackboard, they will benefit from some degree of uplight, which is a form of indirect illumination. Uplight will not only eliminate glare, but will promote uniformity by reducing the contrast between the light source and the surrounding area. A system with uplight will improve the luminance of the ceiling and vertical surfaces, such as blackboards and computer screens. Indirect illumination will also minimize shadows.

Providing too much uplight—100 percent—will result in the “cloudy day” effect. When high levels of indirect illumination are used, footcandle levels may be higher, but students and teachers will perceive the environment as gray—like a cloudy day. Providing some downlight with perforated holes or a lens in the bottom of the lighting fixture will make people think the atmosphere is brighter. They will feel more comfortable.

Light Sources

Although fluorescent systems are probably the most popular for classrooms, other light sources may be appropriate for various areas. Most lamps on the market today can be categorized into three groups: incandescent, fluorescent and high intensity discharge (HID).

Incandescent lamps are the primary source of illumination in most homes. Short lamp life (750 hours) and low efficacy (lumens provided per watt) often limit the suitability of this source for classrooms, libraries and offices.

Fluorescent lamps produce light by activating selected phosphors on the inner surface of the bulb with ultraviolet energy generated by mercury arc. The advantages of fluorescent systems are improved efficacy and longer lamp life (20,000 hours).

HID sources include mercury vapor, metal halide, high pressure sodium and low pressure sodium. The benefits of HID sources are their high efficacy in lumens per watt and long lamp life (20,000 hours). HID is also a point source, which provides the opportunity for better light control.

Specular Reflectors

Specular reflectors may also be used for classroom applications. Specularity is the measure of a surface’s ability to reflect all of the light at the inverse of the angle at which it is received. Specular reflectors are high in specularity (92 percent), and allow for a high degree of light control.

The opposite of specular is diffuse. White paint is diffuse. When light hits white paint, it scatters in many directions because white paint is only 6 percent specular. Very little control can be exerted when a white painted surface is used as a reflector.

Many schools are being retrofit with an industrial channel with a painted baffle under the lamps. This fixture is sometimes referred to as an “ice cube tray” or “egg crate” fixture. Several problems are associated with this type of fixture: it produces non-uniform light, provides poor vertical illumination, and it’s inefficient. Essentially, there is no light control. All of the light is dumped under the fixture.

High vertical light levels are almost impossible to achieve with a baffled fixture because of its mechanical cut-off. The wide photometry produced by the specular reflector, on the other hand, facilitates high vertical light levels.

Using specular reflectors with T-8 lamps and electronic ballasts will often reduce the number of lamps required by half. The result is better uniformity and higher light levels with fixtures that require half the energy.

Color Rendering

To facilitate learning within a classroom or lab, consider color rendering. The higher the color rendering index (CRI), the more vibrant or closer to natural the color in objects will appear. A light source with a CRI of near 100 has the same rendering capabilities as daylight.

Lamps used in the new lighting system installed at Northwood Middle School are TA 33-watt, with an 85 CRI. Jerry White, president, Engineering Consultants Inc. (ECI), Fort Wayne, who designed the lighting, said administrators typically are not concerned about CRI.

“When we design a system for a school, we encourage the customer to consider color rendering to achieve the best possible illumination. Studies have shown that a school’s educational benefits are directly proportional to the quality of the lighting. When students have difficulty reading because of poor visibility, it’s hard for them to gather and retain information,” White said.

Physical Factors

The layout and dimensions of classrooms and offices will help determine what lighting system is best. If you are retrofitting an existing system, you may have recessed fixtures installed in a finished ceiling. Then these fixtures are removed, you will need a lighting fixture that will fit into the opening. If the school is older, the ceilings may be high enough to leave the recessed system in place and suspend the new fluorescent or HID fixtures below the existing units.

Often, the artificial lighting in classrooms and offices is supplemented with daylight from skylights or windows. If this is the case, you may benefit from “daylight harvesting,” which is turning off a select group of fixtures during the day so that only some units are energized. To achieve this, the fixtures must be circuited differently and controlled by a photo cell or relay switch.

Budget Considerations

To keep a lighting retrofit within budget, such factors as energy consumption, lamps and ballast life, installation and maintenance costs must be analyzed. Sometimes a system may cost more initially, but the savings realized over a number of years will justify the expense.

At Northwood Middle School, for example, the new lighting system cut energy consumption by 60 percent and reduced the number of lamps used in classrooms by 50 percent.

“Although the new system was more costly to purchase, the school will save money in the long term because fewer fixtures are installed and they consume less energy,” White said.

Financing Alternatives

When examining budget issues, consider financing alternatives. Check with your local utility company and determine if any rebates (particularly for energy savings) are offered. You should also explore leasing the system versus purchasing it. Consider the system payback. Sometimes a retrofit can be funded by the energy savings that accrue over time.

Future Use of the Space

Keep flexibility in mind when designing the lighting system. Rooms within a school must be versatile. A space that is used as an office today may be utilized as a library, a computer room or lab in the future. The lighting system must be able to accommodate future changes.

Lighting Contractors

Finally, select a reputable company to conduct the retrofit. Check with other schools or businesses that have implemented similar projects and obtain contractor names and recommendations. Determine how long any company you are considering has been in business and ask to visit past installations.

Doing your homework prior to a lighting retrofit will take time. But the results you achieve in terms of quality illumination and cost savings will likely be worth the hours invested.

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