Lighting

Basics of Lighting

basics of lighting

Residential interior lighting is as much art as science. A good residential lighting design is functional and comfortable, blends with the architecture and decor, and helps the owner personalize their home. The result is experienced as work, leisure, living, showcase, castle and sanctuary.

At the start of a project, some interior lighting clients know exactly what they want, while others may still be looking for inspiration. A competitive practitioner offers ideas and general education about lighting, so clients can make the best choices and get exactly what they want. Fortunately, conventional wisdom provides common owner expectations, and best practices and rules of thumb provide useful guidance for practitioners.

This article describes the basics of residential interior lighting design and offers ideas and layout principles for various spaces in the home.

Design basics


The first step is to learn what clients want from their interior lighting. In lighting design, this is called programming. This information can come directly from the client or from a builder’s profile of its home’s intended market. The more you learn about the client’s desires and personality, the better equipped you are to give advice.

Throughout the home, layering is the primary lighting design principle. The general (ambient) lighting layer is for general use (e.g., walking); a good example is a chandelier in a living room, which provides ambient illumination while serving as a decorative element. It fills the room with a soft glow. Localized task lighting, such as pendants over a kitchen island or a portable table luminaire next to a chair or bedside, is added where more intensive tasks are performed. Accent lighting draws attention to focal points, such as wall art. Use daylight for general lighting wherever possible, as that daylight can affect space appearance due to its variability in intensity, direction and color at different times of day. All lighting should be visually comfortable, with no glare or unwanted shadows.

Based on typical activities in each space, ensure proper uniform light levels for safe and efficient completion of tasks. The Illuminating Engineering Society lists typical home spaces and activities with recommended light levels in foot-candles (fc) and lux (lx); see Table 1 for examples. More light can be added where necessary, based on factors such as user age.

Determine how much light output, expressed in lumens, is needed from the lighting to provide the required light level. As 1 fc is 1 lumen per square foot, a 100-square-foot room requiring 3 fc of general lighting means the luminaires need to produce 100 × 3 = 300 lumens.

The number of luminaires required is that number divided by the lumens per luminaire.

We’re not quite done, however. We have to account for light loss due to the size and dimensions of the room and its finishes.

First, determine the room cavity ratio (RCR), which, for a typical rectangular room, is [5 × H × (L + W)] ÷ (L × W). H is the vertical distance between the task plane (an invisible horizontal line intersecting the space where the primary task activity occurs) and the center of the luminaire. L and W are the room’s length and width. If the room is irregular in shape, RCR is (2.5 × H × P) ÷ A, where P is the room’s perimeter length and A is its area in square feet.

Once we have RCR, we can determine the coefficient of utilization (CU) using Table 2. This particular table assumes a 20 percent floor reflectance (medium color, such as light brown), 80 percent ceiling reflectance (white) and 50 percent wall reflectance (pastel paint). A darker finish would reduce CU, while a lighter finish would increase it.

Therefore, the number of luminaires needed to produce a given light level is No. of Luminaires = (fc target × room area) ÷ (lumens per luminaire × CU). If our RCR is 8 (100-square-foot room with an 8-foot mounting height), we would need 731 lumens. If we want to use luminaires producing 450 lumens each, that would be two luminaires.

The above calculation would be conducted for general lighting (e.g., 5 fc on the floor in a kitchen, 3 fc in a hallway) and might be repeated for each zone of task lighting. For accent lighting, the object or area being highlighted should be at least three times brighter than its surround. For important artwork, this could be significantly increased.

An alternative approach in residential lighting design is based on incandescent wattage. For general lighting, multiply the room’s area by 1.5. For task lighting, multiply by 2.5. The result is the minimum amount of lighting wattage needed. For a 10-foot-by-12-foot kitchen, we would need at least 180 watts (W) for the general lighting. For a kitchen island that is 6 feet by 4 feet, we’d need 60W for the task lighting.

The problem with this technique today is that traditional incandescent wattages are disappearing in favor of more efficient lamps that produce similar light output (see Table 3). If you prefer this formula but will be using it in a design that will feature energy-efficient lamping, make a simple adjustment based on the actual lamp that will be used. Better yet, convert to lumens using a benchmark, such as a 60W incandescent. If 120 watts of incandescent lighting are required, that would be 1,600 lumens, which could be provided by halogen, LED or compact fluorescent lamps (CFLs). However, even that lumen output is only roughly equivalent if we’re talking about a similar type of luminaire.

Uniform general lighting may provide good task-light levels, but it can be boring. Task and accent layers should be provided to tell a visual story. In a home, where you put the light is as important as the amount of light delivered. Use it to brighten objects and areas of interest to draw attention. Light can also be used to affect a room’s perceived visual size. To make the space appear larger and draw attention to the architecture, consider indirect or shielded direct ambient lighting that uniformly illuminates high-reflectance (e.g., white but not glossy) walls and ceilings. To make a space appear smaller and draw attention to bright objects instead of surfaces, consider recessed or surface-mounted direct lighting for general lighting.

Another way to draw attention to surfaces and materials is through wall washing and grazing. With wall washing, lights are typically placed at or above the ceiling to smoothly and uniformly illuminate 8–9 feet of wall from top to bottom. The luminaires should be placed far enough from the wall so the light falls on the wall at a wider angle; consider 2½–3 feet as a starting point and adjust as needed.

With grazing, the intent is to reveal rather than wash out texture. Luminaires are placed closer to the wall, so the light falls on it at a narrower angle, producing shadows that reveal texture. Placement can be adjusted farther from the wall to reduce shadowing and closer to heighten it. Luminaires should be spaced apart in accordance with the manufacturers’ instructions.

Note the contribution of these layers to the ambient light level. In some spaces, contribution from decorative, accent, wall wash or task lighting may provide adequate ambient lighting, making separate general lighting luminaires unnecessary. Then general lighting becomes a matter of taste.

Each layer should be separately controlled and dimmed wherever possible. Dimming allows the owner to tune the layers to create lighting scenes that are perfect for different space function, to set a mood or to optimize visual comfort.

A variety of lamps and luminaires is available to provide desired performance while making the right aesthetic statement. Luminaires may be functional or decorative, contemporary or classic comfort. They can stand out or blend with the architecture. Aimable luminaires allow direction of the light beam, which may be further modified into a precise pattern using lenses, filters and louvers. The same or similar luminaires can be used in all rooms featuring a pendant for a unified aesthetic, or different luminaires can be used in each room for a whimsical approach. For a traditional look or to help the lighting blend, consider a symmetrical approach—symmetrical rows of downlights and the same table luminaire at both ends of a couch. Diffuse lighting creates a soft warm glow, while direct lighting such as point-source track lighting can create a sense of tension and sparkle. Many ceiling fans are available with integral lighting or with an optional lighting kit.

The luminaire should be appropriately lamped, with considerations that include lumens, wattage, efficacy (lumens per watt), service life, color temperature (warm, neutral or cool tone), ease of dimming, cost, mercury, resistance to shock and vibration, heat and ultraviolet output, and so on.

Now that we know the basics of design, let’s take a brief tour of individual rooms and spaces.

Foyer


The foyer is the visitor’s first impression of the home. The primary goal of the lighting here is to provide a warm welcome and facilitate safe passage to the rest of the house.

For general lighting, consider a pendant or chandelier for taller ceilings and flush or semiflush ceiling luminaires for lower ceilings.

Scale the pendant to the space—for example, use a vertical pendant such as a lantern in a tall, narrow foyer. Typically, you add the room’s length and width in feet (e.g., 20 feet), which would be a suitable diameter for the pendant in inches (20-inch diameter). The bottom of the luminaire should be about 7 feet above the floor. If using flush or semiflush ceiling luminaires, consider wall sconces or a lamp on a small table for a decorative touch. If stairs lead off of the foyer, they should be lighted uniformly for safety.

Living room


The general lighting in this multifunctional space should fill it with a subtle warm glow that makes it feel inviting and comfortable. The general lighting can be a visual element to personalize the space, such as a chandelier, or blend in with the architecture, such as recessed downlights. Add task lighting in zones where reading and other visually demanding activities are performed and accent lighting (track, undercabinet, etc.) to highlight artwork, family photos, etc.

If using a chandelier, consider mounting it roughly 80-plus inches above the floor. If using sconces, consider mounting with the bottom of the luminaire 60 inches above the floor.

Bedroom


As with living rooms, layering the lighting is critical here. General lighting, usually installed at ceiling height (typically 8–9 feet), should be strong enough to do activities such as dressing but soft enough for comfort at bedtime. Recessed downlights are typically used sparingly, optimally for accent lighting. Shorter or flush-mounted luminaires are popular, though taller ceilings may accommodate a chandelier for a more dramatic statement. Lighting a cove or soffit, if there is one, can produce a very soft atmosphere while highlighting these architectural features. The lighting may be configured to be controllable from both the entrance and the bedside.

Task lighting is typically provided by portable luminaires. Decorative bedside pendants are an interesting option that can be hung low for a sense of intimacy. Wall-mounted luminaires should be positioned just above the level of the head and independently switched. Vanities, work or hobby spaces, reading chairs, and closets all need dedicated lighting. Mirrors over vanities should be sidelighted to avoid facial shadowing.

Kitchen


Kitchens are often considered the busiest room in the home. General lighting can be provided by recessed fixtures or a central chandelier. The American Lighting Association (ALA) recommends mounting recessed luminaires around a room’s perimeter about 30 inches from the wall. For chandeliers, note glass is easier to clean than fabric. Recessed downlights or track lighting can focus on the sink and, if a hood light is not installed, the cooktop.

Undercabinet lighting is a popular way to put task illumination on countertops. Many choices are available from linear to puck lights. Consider placing the linear luminaire toward the front of the cabinet and aiming the light backward. A lensed luminaire will diffuse the light emission, well-suited for glossy countertops, and produce a more uniform appearance. If using linear luminaires, try to match luminaire length as close as you can to the width of the cabinet, and try to position the luminaires as close as possible end to end between cabinets.

Consider small pendants mounted over island counters and breakfast bars for general and task lighting. The ALA recommends mounting the pendants with their bottoms about 66 inches above the floor (it should be possible to look across the room below the pendants). If the counter has seating and the pendant shades are shorter in depth, install with their bottoms a little lower (60 inches above the floor). Generally speaking, one pendant should be installed per 2 feet of counter space. If the luminaires are thin and narrow, consider adding one or two more. As in other design fields, an odd number can create visual interest and a sense of balance.

For kitchen tables, consider a decorative pendant for general and task lighting. The ALA recommends that, if the table is round, the luminaire should be about 1 foot narrower than the table’s diameter. If the table is square or rectangular, it should be 1 foot narrower than the table’s smaller dimension.

The last layer is accent lighting. Options include track, aimable recessed and internal cabinet lighting (e.g., striplights in glass cabinets). If the raised cabinets do not reach the ceiling, another approach is to illuminate the space between the cabinet and the ceiling.

Dining room


In the dining room, activity—and, therefore, illumination—focuses on the table and the faces of people around it. Popular options include recessed or track lighting, a pendant (e.g., chandelier) or a series of small pendants supplemented by recessed or track lighting. If a chandelier is used, it may incorporate a downlight for accenting a table centerpiece.

When using chandeliers, the ALA recommends choosing a luminaire that is at least 6 inches narrower than the table’s narrower dimension. If a table is 48 inches by 72 inches, the width of the luminaire should be about 36 inches. The chandelier should be mounted about 30 inches above the tabletop for an 8-foot ceiling, adding 1 inch for each additional foot of ceiling height. The chandelier’s form should match the table’s; for example, if the table is round, consider a round or globe chandelier.

Accent lighting, such as recessed or track lighting, can be added to highlight artwork, buffets or sideboards, and cabinets. Linear task lighting may work for some sideboards and cabinets. Recessed luminaires should be aimable. The ALA recommends placing recessed downlights in the ceiling 9–12 inches from the wall and 24–36 inches apart for illuminating buffets and sideboards.

Bathroom vanity


Lighting is typically installed around the mirror. If the mirror is small, consider placing a vertical luminaire on each side. The luminaire should be outside the cone of vision (60 degrees) to avoid glare and be mounted at face height, with the luminaire’s center at eye level and its bottom about 60 inches above the floor. The ALA recommends placing the luminaires at least 28 inches apart.

For larger mirrors, consider mounting above the mirror using a strip of vanity lights. The ALA recommends mounting 78 inches above the floor.

Halls


When it comes to good design, hallways are an important but often overlooked element of the home. Uniformity of general illumination, with no dark corners, is important for safety; direct lighting can work, though indirect lighting with reflective walls can work well too. Daylight is optimal. Accent lighting can draw attention to focal points. Task lighting can be added for mirrors and closets.

A rule of thumb for hallway general lighting is to space the luminaires 8–10 feet apart. Divide hall length by 8 and subtract one for a rough luminaire calculation. A 20-foot hall would require two luminaires.

Closets


Closet lighting can contribute to lifestyle and convenience while creating an upscale feel. If the closet is deep enough to enter one step, consider lighting it from the inside. One approach is linear, low-profile LED lights with a warm color temperature. The light could turn on and off using a motion sensor or doorjamb switch. Wireless switches and motion sensors, luminous clothes hangers and battery-powered luminaires are available.

Wall art


The location, framing and illumination of wall art determine how noticeable it is. A painting should appear three times brighter than its surround, requiring accent lighting. To avoid glare, aim the luminaire at a suitable angle, adjusting as needed with 30–45 degrees as a starting point. If the frame is large, a higher angle may be needed to avoid shadows. If the painting has texture that should be emphasized through shadowing, reduce the angle.

Oil paintings tend to reflect light, while acrylic isn’t glossy. If the artwork is mounted under glass, avoid glare with careful lighting placement (such as by using an internally illuminated frame) or, potentially, nonreflective glass.

Heat and ultraviolet energy can damage artwork. Place your hand between the light source and the art; if you can feel heat, it’s enough to damage an oil painting. Avoid light sources with ultraviolet output (e.g., fluorescent) to preserve the painting. Xenon, halogen and LED sources can work well, although halogen lamps do produce significant heat. Incandescent is rarely preferred, because it can visually mute cooler colors, such as blues and greens.

Art and science


The science of residential lighting involves providing suitable light levels with optimal visual comfort and no unwanted shadows. The lion’s share of effort is art—focusing attention where it is needed, conveying an image, making rooms feel intimate or public. As electrical contractors are often called on for information and ideas, it pays to understand the basics of lighting and the many types of luminaires, controls and other options that are available.

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