Week 9: Chapter 5- Mechanical Systems

Chapter 5

Mechanical Systems  

In Chapter 5 we learned about, Designing an effective and sustainable lighting solution, Comparing lamp types and their appropriate uses in an interior, Identifying sustainable lamps and fixture types, Identify lamps and fixture types, Using CRI and CCT to assist in lamp-selection criteria, and Drawing a reflected ceiling plan.

Power companies provide electricity for most buildings. This electricity can be generated by several sources, as mentioned in Chapter 4 in the discussion of fuel sources. The single biggest source of energy use in a building is for electric lighting. Thus, this chapter presents the basic principles of electricity and electric lighting.

Electricity

Electrical current can be either in the form of alternating current (AC) or direct current (DC). In the late nineteenth century, Thomas Edison advanced the electric lamp using direct current. Edison believed that DC power was superior to AC and promoted it as such. Nicola Tesla, another great scientist and inventor working with electrical current, promoted AC power as superior. Unable to convince Edison of this claim, Tesla ultimately transferred his patents to George Westinghouse.

Electricity travels from the utility company to the user through a combination of overhead and underground electrical lines. Transformers are used to step down the electrical current to specific locations and for specific uses. Most residences in the United States use a single-phase, three-wire system with 120-volt and 240-volt service. The majority of outlets use 120 volts, although some appliances and air-conditioning units require the higher voltage, 240 volts. A 120/208 volt, three-phase, four-wire system is used by the majority of commercial buildings.

The rate at which electricity is turned into something else (light or heat) is measured in watts (W). Voltage (V) refers to the electromotive force and current is measured in amperes (A, amps). The relationship between the three measures is expressed as W = V x A. A complete electrical circuit consists of an energy source, the current itself, and a resistor.

Components of Electrical Systems

In circuits with pure electrical resistance (incandescent lamp) Ohm’s Law dictates that I = E/R where I is the current measured in amps, E is the voltage, and R is the resistance measured in Ohms. When a motor or ballast is used for the circuit, I = E/Z where Z is the impedance (inductive resistance) measured in Ohms.

Electrical power grids around the world vary. The number of voltage cycles that take place in one second is measured in Hertz (Hz). The US and Canada operate a 60Hz electrical grid, while most of Europe and many other parts of the world operate on 50Hz.

Electrical power travels across electrical lines to a point of entry at each building it serves. A service drop is used to connect overhead electrical lines to a building. A metal conduit runs the electrical line through a meter that reports power usage to the utility company. The entire system must be grounded to avoid electrical shock and fire. From the meter, electrical lines are run directly to a panel board in residential projects. In larger projects, the electrical lines will first pass through a service switch that can be used to disconnect service to the entire building.

Connection to Building

Electrical power is typically connected to a building using a drop head. The power line is then run through an exterior meter (which must be grounded) and then into the interior electrical panel.

Cable Types

Several types of cable are available depending on the use. Commercial electrical power requires hard conduit, whereas flexible cable (romex) can be used residentially as long as it is enclosed.

Electrical Symbols
Designers use common electrical symbols on electrical plans and need to understand them to read plans from subcontractors. It is important that designers work with other consultants to place switches and outlets that comply with building code requirements while also serving the needs of the building users. Having sufficient numbers of outlets and electrical supply locations that work with furniture placement (both systems furniture and movable furniture) assists users.

Powering Systems Furniture

One of the areas where an interior designer needs to work directly with electrical supply is when integrating systems furniture solutions. There are several ways in which this can be accomplished. The easiest and most flexible way to provide power to systems furniture consists of the raised access floor. In this instance, all power, data, voice, and Internet wiring can be located between the structural floor and the raised finished floor. This type of system allows for furniture to be relocated as frequently as needed. Other power-distribution methods include power poles, bus ducts, undercarpet flat wire, and raceways. Power poles or raceways extend floor to ceiling and provide an easy, although seldom used solution for getting power to office cubicles. Some furniture systems are designed with integrated power poles. A cellular steel decking floor system allows for data and power cells to be located within the floor with floor-mounted junction boxes and outlets. Raceways can be integrated into the floor system with periodic access panels and outlets connected along a grid of branch raceways. Fixed floor outlets can often interfere with circulation or be placed incorrectly for changing office landscapes. Undercarpet flat wire service allows for flexibility in conjunction with carpet-tile flooring installations. Bus ducts (also called bus ways) consist of conductive metal strips that come in standard lengths.

Energy-Management Devices

The use of energy can be managed in several ways. Current estimates indicate that the United States uses about 2 trillion kilowatts per hour (kWh) of electricity per year. Of this, approximately 25 percent goes to building energy systems (primarily lighting, heating, and air). According to the Energy Administration, 86 percent of energy in the US is generated by fossil fuels (natural gas, coal, and petroleum).

WATTAGE AMOUNTS

1 kilowatt = 1000 watts

1 megawatt = 1,000,000 watts

1 gigawatt = 1,000,000,000 watts]

According to the eia.gov approximately 28.9 percent of all energy in a residence goes to heating and cooling. In a commercial application, 2.6 percent is used for heating, 11.9 percent for cooling, 10.9 percent for ventilation and an additional 10.3 percent is used in artificial lighting. The most basic way to reduce energy use is to keep buildings well insulated and lower the thermostat temperature. Lighting-control devices also contribute significantly to energy use reduction. Motion sensors and daylight sensors are commonly used to provide artificial lighting only when a space is occupied or when daylight is insufficient. Dual switching options for rooms are another way to reduce energy towards artificial lighting. Allowing fixtures closest to the windows to be switched off during peak daylight hours reduces reliance on artificial lighting. Operable windows can allow for reduced use of heating and air conditioning in some places during moderate weather.

Interior Design Implications

Interior designers must have a working knowledge of electricity and how it gets distributed in a building in order to properly integrate their designs safely and correctly. The single most potent impact an interior designer can have on the energy efficiency and the ultimate sustainability of a building is through good lighting design. One of the most common mistakes made in a space is over-lighting. By calculating the actual number of fixtures needed, the total can usually be reduced. By accounting for daylighting within a space through the use of separately switched fixtures, energy use can be significantly reduced. The use of daylight-enhancing devices such as light shelves can also reduce the overall energy load of the building. The less lighting used, the less air conditioning needed, because lighting creates one of the biggest heat loads in an interior.

Lighting

Light is defined as the visible part of the electromagnetic spectrum. It is a form of energy that is visible to the human eye. Light does not contain color; rather, the color is a function of the light energy being reflected off of different surfaces, thus appearing as color.

Humans have sought to produce artificial light since they first used fire. Firelight was first supplemented with candlelight. Gas and oil lamps were invented, and finally electrical lamps became readily available in the early twentieth century. It is interesting to note that all artificial light sources--incandescent, fluorescent, and high-intensity discharge (HID)--were originally used as outdoor sources and were only later brought into the interior environment.

Why is the study of artificial lighting important to interior design? There are two primary reasons why an interior designer needs to understand and master artificial lighting. The first is that lighting affects people’s health and welfare. The second is because bad lighting can ruin even the best interior design. Lighting is a critical element of the design process. Mastery over how it works is crucial for creating a good design. To be a competent interior design professional, knowledge of lighting is required.

Behavior of Lighting

As electromagnetic waves, lighting reacts in various ways when it meets a solid surface. Depending on the material of the surface, the light may be reflected, refracted, transmitted, diffused, or some combination of these outcomes.

Psychology of Lighting

John Flynn, a noted environmental psychologist, completed some of the earliest studies of the effects of lighting on people. His research demonstrated how people perceive different levels and types of lighting. Specifically, he sought to explain what types of lighting levels result in the perception of public space versus private space. Similarly, he tried to explain perceptions of warmth and coolness based on color temperature of the artificial lighting in a space.

• Perceptions of Public/Private- How lighting is distributed within a space affects how people view that space. Shadows in the corners combined with high contrast tends to create a space that is perceived as private or intimate, whereas an overly lit room with little to no contrast in light level creates a public and open feeling.
• Cool versus Warm- The color temperature of light and the colors used within a space affect whether the space feels cool or warm. People tend to perceive warmer light sources (incandescent) and warmer color palettes as warmer. By contrast, the use of cool light sources (fluorescent) combined with blue, for example, will be perceived as cooler, though the actual temperature of the rooms may be identical.
• Health and Lighting- Several research studies have been conducted to assess the impact of lighting on humans. Good lighting has been associated with improved worker performance. Control over light levels correlates with higher employee satisfaction. Research demonstrates that daylight within classrooms improved children’s test performance. Other studies have indicated that shift workers run an increased risk of serious diseases such as cancer. The apparent cause of this is disruption to the natural circadian rhythm within the human body, which responds to light levels in the environment through a complex series of chemical changes. People who work all night and do not have “normal” exposure to sunlight can suffer the consequences of an upset circadian rhythm. Studies show that all living things--plants and animals--have some form of circadian rhythm and are impacted by light. Although all of the impacts of natural and artificial lighting have not been studied, several causes of discomfort can be identified and avoided through proper lighting design.
• Glare- Glare is created by an excessive amount of light coming into people’s eyes from the wrong direction. For example, when an overhead fixture has a visible lamp that is within the line of sight, this is perceived as glare. This is termed direct glare. Indirect glare also causes visual discomfort. This problem frequently arises when a light source reflects on a computer screen or visual display terminal. Glare can be avoided through the careful placement of luminaires or by using diffusers. The eye functions much like a camera. Images are transmitted via the parts of the eye to the optic nerve and are then perceived in the brain. The lens allows the eye to focus, and the iris expands and contracts much like the aperture on a camera, admitting more or less light as needed. Because of the location of the optic nerve slightly off center at the back of the eyes, a blind spot is created. The brain compensates for this by filling in the information. This phenomenon also results in our ability to perceive depth.
• Proper Terminology- One of the first things to clarify in your mind when learning about lighting is that what you have called a light bulb your entire life is actually a lamp, and what you have called a lamp, in reality, a fixture that holds a lamp. Together the lamp and fixture (plus a ballast any other items require to make a functioning light source) form a luminaire.

Lamps and Their Appropriate Applications/ Energy Implications

Incandescent

The incandescent light source provides lighting for most homes in the western hemisphere, particularly in the United States. Only recently has this source come under severe scrutiny. Incandescent lighting is warm in appearance and is perceived by most westerners as a flattering source of artificial lighting. It is easily dimmed to create a variety of moods within a space. Although inexpensive to purchase, the incandescent lamp is very inefficient and gives off more heat than light. As a result, entire countries, such as Australia, have vowed to replace the incandescent lamp with other light sources that are considerably more energy efficient. In 2009, legislation was enacted to phase out many incandescent lamps by requiring increased levels of energy efficiency. In 2012, 100-watt incandescent lamps were phased out, followed by 75-watt lamps in 2013 and 40- and 60-watt lamps in 2014. Manufacturers have responded by developing A-shaped LEDs, additional shapes of Compact Fluorescents (CFLs) and energy efficient versions of the traditional A-shaped incandescent. CFLs and LEDs use 75 percent less energy and last longer (CFLs are rated for 7 years and LEDs estimated for 22 years).

The primary use of the incandescent lamps outside of residential applications is in retail. The halogen lamp, a form of incandescent originally developed for slide projectors, is now commonly used in some restaurants and certain types of retail space--especially jewelry stores, boutiques, and other locations--to highlight specific merchandise or to create a specific mood.

Circadian Lighting

Human beings have biological cycles that vary throughout the day, year, and lifetime. Recent studies have shown that having the proper type of light throughout the course of the day can improve human health when working and living under artificial light sources. The goal of circadian lighting is to simulate the daylight provided by the sun throughout the course of the day with the bluest light being in the middle of the day with lower color temperatures in the late afternoon and early evening hours. The WELL Standard includes circadian lighting design as a component of promoting and supporting human health indoors.

Germicidal Lighting

Germicidal lighting is becoming increasingly more popular in light of the need to prohibit the spread of germs in interior environments. The IES has issued guidance on using ultraviolet radiation to kill germs in interior environments focusing in UVC radiation. Unfortunately, UVC lighting is also the most hazardous for people. Germicidal UV lighting (GUV) is lighting in the short wave of the electromagnetic spectrum (200­280 nanometers) and can be used for surface disinfection. Some lighting companies are also working on LED versions of safe white light.

Halogen

The halogen lamp is a form of incandescent. The first halogen lamps introduced into interior design were the MR-16s (multi-faceted reflector 16/8 inch, or 2 inches in diameter). The original purpose of the MR-16 was projection. Its value to interiors derived from its ability to provide a strong focused beam of light particularly effective in illuminating display items and artwork. Halogen light is much whiter than regular incandescent, though it is still a warmer light than most fluorescent sources.

Fluorescent

The majority of commercial spaces in the US and Canada use fluorescent lighting sources. Fluorescent lamps provide an energy-efficient, long-lasting, and economical choice for this type of application. Recent strides have been made in reducing the amount of mercury contained within fluorescent lamps as well as to improve the color temperature of the light source when a warmer light is preferred. High color temperatures and high color rendering indexes are possible with fluorescent sources, although the cost is also higher. Fluorescent lamps do introduce a couple of sustainability challenges. First, the disposal of the lamps introduces mercury into the landfill. Secondly, compact fluorescents include integrated ballasts within the lamp to allow for use within standard incandescent type fixtures. As a result, each time one is thrown away, the entire lamp and ballast enter the waste stream.

 The same legislation used to phase out many forms of incandescent lamps also phased out all 4-foot long 1.5-inch-diameter tubular fluorescents (T-12) and most 8-foot T-12 lamps in 2012.

High-intensity Discharge (HID)

Traditionally, most types of high-intensity discharge (HID) lamps have been used in outdoor applications such as street lighting, roadway lighting, and landscape lighting. Parking garages and factories exemplify the only interior applications of these sources, with the exception of metal halide. As the whitest of the HID lamp sources, metal halide lamps are often used in recreational facilities, warehouses, and big box stores. In the past decade, metal halide sources have been developed with high color rendering indices and a whiter light, making them a suitable choice for retail lighting, particularly in hard-to-reach locations. As these lamps age, the color of light provided can vary and the difference is visible. The majority of the other sources still operate in the yellow range of the color spectrum, making color rendering difficult.

Light Emitting Diodes (LEDs)

Light emitting diodes (LEDs) were introduced into the marketplace as the energy­efficient answer to interior lighting in the early part of this century. It should be noted that this technology is still relatively new. The subject of whether this is the fourth interior light source and ready for use as ambient light has been the subject of many recent articles by both lighting designers and architects (DiLouie and Willmorth, 2008; Broderick, 2008; and Sullivan, 2007). Concerns over this exciting new light source seem to center on the lack of photometric data available from manufacturers and actual lumen output of LEDs. In recent CALiPER testing, 4-foot linear LED replacement lamps used in place of standard T8s or T12s were found to fall short of manufacturers’ claims (Broderick, 2008). None of the LEDs tested provided even half the light output of the fluorescents. LED standards have been produced by the Illuminating Engineering Society of North America (IESNA, 2010). To produce white light from LEDs, one of two things is done: either red, blue, and green diodes are combined to create white light, or white is produced through the addition of a phosphor coating. Despite the concerns over LEDs for general illumination, many designers are incorporating them into interiors at a rate that is faster than manufacturer data is produced. The primary benefit of the LED is energy efficiency.

LEDs differ from other interior light sources in several ways. Traditional light sources require reflectors to distribute light to an interior. LEDs are smaller, directional and very precise. The high degree of accuracy relies on refraction of light versus reflection of light. Thus, 100 percent of the light is refracted and none is lost. With LEDs, several small lower-intensity lights work together to create a consistent and reliable light source. The smaller size allows for easier integration into the architectural elements of a building. LEDs can be easily customized for the location and intended use. When used on coves, no end light loss occurs as traditionally happens when using fluorescent strips. Further, LEDs can be easily curved, unlike the linear fluorescents.

One of the concerns with LEDs has been over color consistency and variations in color from bin to bin. Manufacturers have determined that using a method of bin mixing to achieve an overall color consistency can be easily replicated from fixture to fixture.

LEDs can have a correlated color temperature between 2200 and 6500 degrees Kelvin and are dimmable with 100 percent precision maintaining the color of the light. The enemy to LED lighting is heat. The hotter the light source is, the shorter its lifetime. Thus, a designer must pay attention to how heat is managed within a fixture. LEDs can last anywhere from 10 to 20 years, and the quantity of light output (measured in lumens) decreases over time. Thus a measure, L70, is used to indicate when the output drops to 70 percent of the initial lamp lumens. Because of their long lifetimes, LEDs do not need to be as easily accessible as other traditional light sources. However, it is important that the driver/power supply be accessible in the event it fails as these are rated for 25,000 to 50,000 hours. As long as the driver can be replaced separately from the LED board itself, the fixture can last the duration of the estimated life. With LEDs the light source and the fixture are integrated--in other words, lamps cannot be replaced without replacing the fixture. Only the power source can be replaced.

Correlated Color Temperature (CCT)

Each lamp has a correlated color temperature (CCT) that is provided in degrees Kelvin. The CCT describes how white the light emitted appears as compared to sunlight. A higher CCT makes for a cooler (bluer) appearance, whereas a lower CCT looks warmer.

Color-rendering Index

All lamps have a color-rendering index (CRI). The CRI of a lamp measures its ability to render color. This ability to render color is rated on a 100-point scale with 100 being the best and 0 the worst. The measurement is based on a standard reference comparison of eight colors. It is important to remember that the CRI is the average of how the light source renders the eight colors. In other words, two different lamp types with a CRI of 80 may not look the same when used.

Most everyone has experienced the phenomenon of metamerism. When selecting two socks under incandescent lighting, both appear to be black. However, under sunlight the color of the socks is actually navy blue--this is metamerism. The color of the light source will actually determine the color we see when we view an object. Things that appear to match when viewed beneath one light source, may not match under another. Consequently, it is extremely important to select colors, textiles, materials, and all other interior finishes under the actual light source that will be used in the finished space. It is also important to specify both the CRI and color temperature of the lamps to be used, to ensure that no metamerism occurs within the design product. Together, color temperature and CRI impact how an interior space will feel and look. Figure 5.21 captures the range that most people find comfortable. The following figures indicate how to read lamp designations for various types of lamps including incandescent, fluorescent, and high-intensity discharge.

IESTM-30-15

The Illuminating Engineering Society (2015) created the IES Method for Evaluating Light Source Color Rendition in response to the need of new ways of evaluating LED light sources. This technical memorandum describes the use of 99 color samples as evaluated under up to 4500 K, between 4501 K and 5499 K, and above 5500 K. It was developed to take into account deficiencies in the CRI and is considered to be much more accurate in measuring color rendition. As with CRI, it is inappropriate to compare the TM 30 of lamps with different CCT (correlated color temperatures).

Fixtures

There are several types of light fixtures for a variety of uses. Some of the most common light fixtures include wall sconces, pendants, wallwashers, uplight fixtures, downlight fixtures, uplight/downlight fixtures, suspended fixtures, recessed fixtures, and surface­mounted fixtures. Each fixture type provides a slightly different light distribution. When selecting a fixture for a project, it is critical to obtain the specification sheet to determine the actual light pattern provided by the specific fixture.

Cut Sheets

Fixture manufacturers produce cut sheets for their light fixtures. These include information about the construction of the fixture, the electrical requirements, available finishes, lamp requirements, size, and operation.

Sustainability and Lighting Design

Lighting accounts for the single largest percentage of energy use in buildings. As such, it is critical to understand issues of sustainability as they relate to lighting design and fixture and lamp selections. Simply put, energy efficiency of a light source can be determined based on the amount of energy needed to produce the light output in lumens and is expressed as lumens per watt (LPW).

A second measure to consider is the effectiveness of the fixture in putting light where light is needed. Correctly controlling the distribution of light can reduce or eliminate glare, light trespass, and light pollution. Light trespass occurs when light from one building spreads to an adjacent building. Light pollution occurs when light is directed into the night sky or other areas, disrupting wildlife. Examples include disruption of sea turtles’ mating process through light pollution in coastal areas and the impact on migratory birds from light levels in the sky. The International Dark Sky Association (IDA) seeks to halt environmental light pollution.

Manufacturers are now working on lamp and ballast recycling programs to divert these from the landfill, and in the case of fluorescent lamps, to recapture the mercury before it is released into the environment. The 1995 US Environmental Protection Agency Universal Waste Rule requires companies handling and consuming fluorescent and HID lamps to recycle them. Litecontrol, based in Hanson, Massachusetts, has had its entire product line cradle-to-cradle certified (Casey, 2008).

Green Seal's Lighting Recommendations

Compact Fluorescent

Green Seal Standard GS-05 outlines requirements for compact fluorescent lamps. Not for use in spaces with extremely high ceilings, where a tight beam of light is required, where the temperatures are extreme, on a dimming circuit for some lamps (there are some dimmable fluorescent lamps on the market), or where electromagnetic interference is likely.

High-Intensity Discharge

• For open offices, hallways, atriums, meeting areas, and other general lighting: metal halide with a CRI of 60 or more.
• For general assembly, manufacturing or retail: metal halide with a CRI of 70 or more.
• For warehouse and loading areas: high-pressure sodium.
• For sport/gymnasium and specialty retail: metal halide with a CRI of 70 or more.

Linear Fluorescent

• Choose T-8 lamps and electronic ballasts.
• Choose lamps with the lowest possible mercury content for your application.
• Consider a 2-lamp or 3-lamp two-by-four fixture.
• Consider 2-foot-long T-8 lamps with two-by-two fixtures.
• Polished aluminum in troffers can create glare.

Sensors

Sensors automatically control the flow of electrical current to light fixtures. Depending on the use of the space, different types of sensors are used.

Automatic Sensors

One of the best ways to reduce energy is to harvest the available daylight. A variety of sensors are available for use in conjunction with daylight harvest. These include open-loop and closed-loop systems. In the open-loop system, solar sensors measure the daylight and control the electric lighting to maintain a uniform lighting level. These must be set up and are not subject to changes within the space and lumen sensors. Closed-loop systems measure the illuminance on the work surfaces, and are quick to set up.

Vacancy Sensors

Vacancy sensors automatically turn off the lights when a space is not occupied. The energy savings resulting from the use of vacancy sensors is estimated between 30 percent and 50 percent. Three types of vacancy sensors are available: passive infrared, passive acoustic, and ultrasonic. Passive infrared sensors sense body heat; ultrasonic sensors send out sound waves to detect changes in the space; and passive acoustical controls rely on microphones to detect human sounds.

Lighting Metrics

Five lighting metrics are used to quantify lighting. The science of light is called photometry. Photometries describe the recorded measures of light as described by the lighting metrics. Each lighting manufacturer provides photometric data for their fixtures with different lamps that the fixture can accommodate.

Luminous Flux

Luminous flux (φ) is the time rate flow of light. The unit of measure for luminous flux is lumens and this measures the total amount of light emitted by a lamp.

Luminous Intensity

Luminous intensity (I) is the directional force causing luminous flux to be emitted. It is measured in candelas. Candlepower distribution curves show the luminous intensity distribution as measured in candelas at various distances in multiple directions from a light source.

Illuminance

Illuminance (E) is defined as the density of luminous flux incident at a point on a surface. The unit of measurement is the footcandle. Illuminance is what most lighting calculations use to determine the number of lamps and fixtures to achieve certain levels of lighting for various spaces as required by either the building code or as recommended by the Illuminating Engineering Society.

Luminance

Luminance (L) refers to the luminous intensity of a source in a particular direction divided by the area of the source. The unit of measure is candela per square foot.

Luminous Exitance

Luminous exitance (M) describes the density of luminous flux leaving a surface in all directions at a point. The unit of measurement is lumens per square foot.

Designing with Light (Design Process)

The list below provides an overview of the steps taken in the design of a lighting system.

Identify the spaces and the tasks within them.

• Verify the number of footcandles required for the task.
• Select the best lamp type for this application (color temperature, CRI, energy efficiency, cost).
• Select luminaire consistent with design concept for the space.
• Do lumen calculations to determine the number of lamps and luminaires required.
• Analyze daylight in the space and how this will impact the need for artificial lighting.
• Create solutions for handling and managing the daylight.
• Do lighting layout.
• Create a three-dimensional model of lighting to study distribution--show some pictures.
• Design special lighting effects to emphasize architectural elements of the space--show some lighting details--provide sketches of your design ideas.

The Lighting Design Packet for Each Phase

• Programming-- information identifying spaces, tasks and required illumination.
• Schematic design-- sketches of desired lighting effects; how each one coordinates with design concept and architecture.
• Design development-- selection of lamps and luminaires, lighting calculations.
• Construction documents-- spec sheets for lamps and luminaires, final drawings reflecting ceiling plans including dimensions, notes and details, lighting fixture schedule.
• Post-occupancy evaluation-- an important step that is often omitted is the post-occupancy evaluation where the designer goes to the site after completion to determine if the occupants are satisfied with the lighting design and that everything is working as intended.

Lighting Plans

The critical pieces of documentation used to convey lighting design intent to a contractor are the lighting plan, specifications, and any design details for specialty lighting installations. These documents must be clear and complete and must include all information needed to create a finished solution while leaving no design decisions to chance. Fixtures and lamps should be specified, including information on color temperature and color-rendering index. Failure to include all of this information may result in unintended results, metamerism of colors, and other design failures.

Conventions for Lighting Plans

For easy understanding by electricians, contractors, and other tradespeople in the field, it is customary to use a reflected ceiling plan, which is a layer added to the floor plan. In a computer-aided drawing (CAD) program, this would be a separate layer to show lighting. By hand, the floor plan is traced onto a separate drawing for lighting. Standard symbols are used for reflected ceiling plans but may vary slightly from office to office; therefore, always provide a legend or key explaining what the drawing symbols being used indicate. The best resources for standard designations are Graphic Standards and other commonly used resources. In addition to a lighting plan, reflected ceiling plans and electrical plans are also commonly used.

Daylight

One of the most important things to consider for a sustainable lighting solution is the sunlight that is available to be harvested. Daylight is usable sunlight that should be included as a part of the lighting design. Various spaces have different levels of recommended daylight that is measured using the daylight factor (DF). The daylight factor consists of the percentage of sunlight that meets the interior workspace. Readings from an external illuminance sensor (light meter) are compared to the average of the reading on the interior at work surface height. The number is then expressed as a percentage or decimal. LEED Rating systems recommend a 2 percent DF for 75 percent of regularly occupied spaces.

Daylight penetration into a space can be predicted by multiplying 2.5 times the height of the window. A light shelf is a horizontal shelf installed inside the space along the window wall. Light shelves can be used to enhance daylight penetration. When used, they should be installed above eye level in spaces with high ceilings and high windows.

In order to determine whether a space will appear to be well daylit or dimly daylit, the following formula can be used to calculate the average daylight factor (ADF):

• τ = transmittance of glazing
• A g = net glazing area
• θ = angle (in degrees) of visible sky in the vertical plane
• A s = total interior surface area, including fenestration
• R = weighted average reflectance values of all interior finishes including fenestration

Once calculated, the following applies: an ADF greater than 5 percent will appear well daylit, while one less that 2 percent will appear dim. (When clear glass is used, clean glass has a transmittance of 92 percent, while dirty glass has a transmittance of 82 percent.)

Sustainable Lighting Design Principles

When designing for sustainable lighting design, some basic principles apply. First, use daylight as much as possible. Allow it to penetrate as deeply into the space as is feasible while controlling for glare using shades, blinds, or other window treatments. Use daylight sensors, dimming and dual switching to be able to adjust the lighting to different levels throughout the day. Use occupancy sensors on spaces that are not continuously occupied. Calculate lighting such that spaces do not become overly lit, thus wasting energy. Select energy-efficient lamp types and fixtures. Consider the entire life cycle of both the lamps and fixtures rather than focusing on initial costs only. Specify light-colored finishes that reflect more light, allowing for the use of fewer luminaires. Finally, allow for individual control of lighting levels in individually occupied spaces when possible.

Blogging Activity 

I chose to sketch this picture: