Lighting and Illumination
Lighting is the single most critical element that can influence the quality of the perceived video. It is affected by the dimensions (width, depth, and height) and angles of wall surfaces of the room; the diameter of the camera lens (known as the aperture); and the color and reflectivity of wall, floor, and ceiling surfaces. Too much light, and the room will feel like a recording studio and will be uncomfortable for the participants to sit in for long durations of time. Conversely, a room that is not lit well enough will appear dark on camera, shadows will appear around the face and neck of participants and in the corners of the room, and the perceived quality of the video will suffer.
Have you ever wondered how television and movie directors record such vibrant looking scenes, or how camera crews can take a picture of a room that looks so stunning and realistic? The secret is in how they illuminate the environment. Film and camera crews use special studio-quality lighting to illuminate their subjects in just the right way to produce the richest, most vibrant images possible. If you've ever been on stage, in a recording studio, or in a photo shoot, you'll probably recall how warm, bright, and uncomfortable it was under those lights. The primary goal of these environments is to illuminate the face of the subjects, along with their background environment, so that they look good on camera.
Conversely, the average conference room or meeting room and cubicle and hallway environments in office buildings are generally designed to provide a warm, soft lighting environment that is comfortable to work in for long durations. The primary goal of these environments is to illuminate table and work surfaces where people write or type on computer keyboards.
The goal of a TelePresence room is to strike just the right balance between studio-quality lighting and comfort for the participants. The participants and the environment around them must be illuminated properly to produce the most realistic, lifelike video quality. However, the environment should be comfortable enough for the participants to sit in it for hours without developing a headache or eye strain.
The three aspects to the design of lighting within a TelePresence room follow:
- The angles and direction of the light and which surfaces it illuminates
- The temperature or color of the light
- The strength or intensity of the light
The following section begins by investigating the angles and direction of light required.
Considering Light Angles and Direction
In a three-point lighting system, three points, or directions, of light influence what the camera sees:
- First, the light that fills the entire environment is ambient light, or fill light. This light generally comes from fixtures in the ceiling to blanket the room in even, well-distributed light.
- Second, the light that falls on a participant's face is participant light, or point light. This light illuminates the face to reduce shadows around the eyes, neck, and other such surfaces that directly face the camera. Point lighting generally does not exist in the average conference room and, therefore, must be supplied as part of the TelePresence system.
- Third, the perceived depth in an image as viewed by a camera is best when the subjects' shoulders and the tops of their heads are gently illuminated, causing them to "pop out" from the background behind them. This is shoulder lighting, or "rim lighting and is optional for a high-quality TelePresence image. You can also use rim lighting to illuminate the wall behind the participants to achieve a similar effect (depth in the perceived image).
Figures 8-23 through 8-26 illustrate the effects of fill, point, and rim lighting on a subject.
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Figure 8-23 A subject on camera with fill lighting only
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Figure 8-24 A subject on camera with point lighting only
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Figure 8-25 A subject on camera with rim lighting only
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Figure 8-26 A subject on camera with 3-point lighting
The critical types of light for a TelePresence solution are ambient (fill) and participant (point) lighting. Shoulder (rim) lighting is optional and left to the discretion of the customer whether to implement it. The remainder of this section focuses on ambient and participant lighting.
Before getting into the details of how to design the proper amount of ambient and participant light into the room, let's quickly touch on the concepts of light color temperature and intensity.
Considering Light Color Temperature
The color temperature of a light source is effectively a measure of how yellow, white, or blue it appears. The system of measurement used for rating the color temperature of light bulbs is the Kelvin (K). Incandescent light bulbs produce a yellowish light, with a Kelvin rating of approximately 2800K. The average fluorescent light bulb used in commercial construction is 3500K. Studio environments typically use 5000K fluorescent bulbs that produce a white light. Lower color temperatures are easier on the eyes and, hence, their popularity in homes and office buildings; however, they do a poor job of illuminating things sufficiently to make a subject look good on camera. By contrast, a room lit with 5000K fluorescent bulbs will make you look fantastic on camera but will be uncomfortable to sit in for long durations. After much trial and error during the early phases of design on the CTS-3000, Cisco found that the best color temperature to use in TelePresence rooms is 4000K to 4100K. Incandescent light bulbs do not produce this temperature of light, and, therefore, fluorescent bulbs and fixtures are recommended. Fluorescent light bulb manufacturers use different "friendly" terms to describe the temperature of their bulbs, such as "cool white," but in most cases they also print the Kelvin rating on the bulb. For those that do not print the Kelvin on the bulb, you can usually look it up on the manufacturer's website based on the part number printed on the bulb.
Measuring Light Intensity
The intensity or strength of a light source such as a fluorescent bulb is effectively a function of its wattage. There are various systems of measurement for this, including lumens, lux, foot candles, and candela. Cisco has chosen to standardize on the lux measurement in all TelePresence-related documentation. Lux is a measure of the intensity of light within a volume of space. It is also a measure of the intensity of light that hits a surface, such as a wall, a subject's face, or a table surface. The lumen, by contrast, is a measure of how much light is emitted by a source. So although a bulb produces light in terms of lumens, what you're actually concerned with in a TelePresence room is how much lux it provides at various points within the room. The average conference room or meeting room found in corporate environments is approximately 150 lux to 300 lux. This is much too dark for the aperture of a camera to sufficiently capture a human subject in good detail. By contrast, the average studio environment is approximately 700 lux, which is much too bright for humans to be comfortable for long durations. After much trial and error during the early phases of design on the CTS-3000, Cisco found that the ideal light intensity for a TelePresence room is 400 lux.
To summarize, the goal is to fill the room with 400 lux of well-distributed ambient light, using fluorescent bulbs with a color temperature of 4100K. However, when measuring the light within the room, it is critical to understand the angles from which lux is measured within a TelePresence room.
Cisco uses a tool called a lux meter to measure the intensity of light at various points within the room. There are essentially four different angles from which light should be measured:
- From the camera's point of view, looking toward the participants
- From the participant's point of view, looking toward the cameras
- From the participant's point of view, facing upward toward the ceiling
- From the perspective of the side and back walls
Cisco divides the room into sections, or zones, to measure light from all these different perspectives. Figure 8-27 illustrate the zones of a CTS-3000 room.
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Figure 8.27 CTS-3000 illumination zones—top down view
Zones 1 to 3 provide a measure of how much light is seen from the perspective of the cameras. Zones 4 to 6 provide a measure of how much light is seen from the perspective of the participants, and hence how well lit the participants will look on camera. Zones 4 to 6 also measure how much downward light strikes the shoulders of the participants and the table surface. Zones 7 to 9 provide a measure of how much light reaches the back wall. Within each zone, it is important to note the direction from which the light should be measured. In zones 1 to 3, the measurement is taken with the lux meter facing the participants. In zones 4 to 9, the measurement is taken with the lux meter facing the cameras. In zones 4 to 6, there is an additional measurement taken with the lux meter facing up toward the ceiling at shoulder height. Figure 8-28 illustrates the direction the lux meter should be facing within each of the zones.
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Figure 8-28 CTS-3000 illumination zones—side view
In zones 1 to 3, the light is measured with the lux meter facing toward the participants at approximately 5 feet (1.5 meters) from the floor. In zones 4 to 6, two separate measurements are taken:
- One with the lux meter facing toward the cameras at approximately 5 feet (1.5 meters) from the floor.
- The second with the lux meter facing up toward the ceiling at approximately 4 feet (1.2 meters) from the floor.
Finally, in zones 7 to 9, the light is measured with the lux meter facing toward the cameras at approximately 5 feet (1.5 meters) from the floor. Throughout all 9 zones, the light should measure approximately 400 lux, except for the second measurement in zones 4 to 6, in which the light should measure approximately 600 to 700 lux. No point in the room should measure lower than 150 lux or higher than 700 lux. Areas that are lower than 150 lux appear completely black on camera, and areas that are higher than 700 lux appear washed out on camera.
By following this methodology for measuring light within your TelePresence environment, you can achieve the best quality video and consistent, reproducible results. Although the illustrations provided are specific to the CTS-3000, you can use the same methodology in smaller or bigger rooms by simply shrinking or increasing the size and number of zones.
Light Fixture and Bulb Considerations
Fluorescent bulb manufacturers specify bulb intensity in terms of how many lumens they produce, but you are concerned with how much light they provide (in terms of lux) at various places throughout the room. The challenge, therefore, is to identify the number of bulbs per fixture, the number of fixtures, and the wattage per bulb required to achieve the desired amount of lux throughout the room. An expert lighting consultant can assist you to determine the best lighting configuration for any given room, and there are lighting design software applications on the market to help you determine precisely which type of fixture, how many bulbs per fixture, and what wattage of bulb you should use. Cost is obviously an important factor as well, so the ultimate goal is to find the right combination at the best possible price. This can also vary by city and by country because of the variety of fixture manufactures and construction costs in various parts of the world. The following sections provide some recommendations on the types and quantity of light fixtures that have been used successfully in Cisco TelePresence rooms to date.
The two most common types of ceiling light fixtures used within TelePresence rooms are pendant-style fixtures that hang down from the ceiling and recessed fixtures that are recessed within the ceiling. Both types are further broken down into three subtypes based on what direction the light is thrown: 100 percent direct, 100 percent indirect, and direct-indirect. Figure 8-29 and Figure 8-30 illustrate these various types of fixtures.
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Figure 8-29 Example of 100 percent direct light fixtures
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Figure 8-30 Example of 100 percent indirect light fixtures
One hundred-percent direct light fixtures direct the light straight down instead of dispersing it evenly throughout the room. Therefore, the light will be more intense directly under the fixture compared to the perimeter of the area, or zone, in which it's measured. This results in hot spots on camera where the tops of people's heads and table surfaces is extremely bright and washed out, but the background areas such as wall surfaces are darker and shadowed. Therefore, 100-percent direct light fixtures are not recommended.
One hundred-percent indirect light fixtures function by directing light upward toward the ceiling or by refracting the light off a reflective surface within the fixture. This allows the light to be more evenly distributed throughout the room. As illustrated in Figure 8-30, indirect light fixtures can either be hung from the ceiling as a pendant-style fixture or recessed in the ceiling. Both types are recommended, but which one you ultimately decide to use depends on the dimensions (width, depth, and height) of the room.
Both pendant-style and recessed-style fixtures are also available in direct-indirect configurations, where a portion of the light (for example, 20 percent) is directed downward while the remaining portion (for example, 80 percent) is directed upward toward the ceiling or reflective surface within the fixture. These are not recommended for the same reason that 100-percent direct fixtures are not—the portion of light that is directed downward could create hot spots. Figure 8-31 illustrates the difference between a direct and indirect fixture and a 100-percent indirect fixture.
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Figure 8-31 Direct and indirect light fixture versus 100-percent indirect light fixture
Another aspect of indirect light fixtures is the degree of dispersion, which is a measure of the angle at which light is thrown from the fixture. The greater the degree of dispersion, the less fixtures are required to provide the same coverage of an area. Figure 8-32 illustrates the difference between a standard fixture that has a degree of dispersion less than 60 degrees and a higher-end fixture that has a degree of dispersion greater than 60 degrees.
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Figure 8-32 Light fixture degrees of dispersion
Now, consider some example 100-percent indirect ceiling fixture arrangements, based on different room dimensions. These examples assume the use of a CTS-3000 room measuring 20-feet wide x 15 feet to 20-feet deep (6.096 meters wide x 4.572 meters to 6.096 meters deep). Figure 8-33 illustrates the recommended number and placement of fixtures using standard quality 2-feet x 4-feet (.609 meters x 1.219 meters) recessed fixtures.
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Figure 8-33 Example CTS-3000 using standard recessed light fixtures
You can also achieve the same results using a higher-end model of fixture that provides either more bulbs per fixture (for example, four bulbs instead of two), run at a higher wattage level per bulb (for example, 80 watts instead of 40 watts) or with a higher degree of dispersion. Figure 8-34 illustrates this arrangement.
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Figure 8-34 Example CTS-3000 using higher-end recessed light fixtures
Likewise, you can achieve the same results using 100-percent indirect standard suspended light fixtures. Figure 8-35 illustrates this arrangement for a room that is 15-feet deep (4.572 meters deep), while Figure 8-36 illustrates this arrangement for a slightly deeper room.
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Figure 8-35 Example CTS-3000 suspended light fixture for a 15-foot deep room
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Figure 8-36 Example CTS-3000 recessed light fixtures for a 20-foot deep rooms
Light Fixture Ballast Considerations
The last item to consider when choosing a light fixture is the type of ballast it uses. The ballast is the device within the fixture that regulates the flow of power through the bulb. Fluorescent light fixtures have two types of ballasts: magnetic and electronic. Although magnetic ballasts are frequently preferred for their durability and long life, they produce a flickering effect on the TelePresence video because the cameras operate at a different frequency than the light fixtures. Therefore, electronic ballasts are required for Cisco TelePresence rooms.