by John Carlson, Systems Engineer, Sound Vision, Inc.
Lighting is far from ideal in many videoconferencing rooms, but there's a lot you can do to improve the situation, says Gerard Darville, Pro-AV Sales Manager at Lutron Electronics.
The way lights are used in a broadcast studio, he explains, can serve as a model for superior video conference lighting. Instead of big track-mounted studio floods, what we need are special fluorescent fixtures, designed to act as key and fill lights, but recessed into the ceiling like standard office lights.
"We know studio lighting would not be practical in most conference rooms," he says, "but we can apply what we learn from the studio and get very good results."
According to Darville (drawing from the IES design guide, Fundamentals of Lighting for Video Conferencing) there are five design considerations that are crucial to the image quality you'll get from your VTC equipment.
1. Main lights
Lighting from a single, diffuse fixture at about 45° to the side of the subject’s face and 45° from vertical. Use of Lutron VTC fixtures, below, produces a similar effect, though softer.
In a broadcast studio, Darville explains, you would typically mount key lights at about a 45° angle to your talent, also angled at 45° from vertical. By doing so you produce pleasing shadows defining your subject's eyes, nose and other features–not the unflattering shadows you'd see if the light was directly overhead or directly to the side (see illustration).
You would also mount more diffuse fill fixtures on the opposite side of the subject (though also at 45° from vertical). These fixtures partially fill in shadows and produce a softer effect than a key light used alone.
Lutron has an elegant way to produce this kind of lighting in a conference room. They offer a recessed florescent video conference light with a reflector shaped to reproduce an effect similar to studio lights. These fixtures throw light at a 45° angle, rather than straight down. Darville suggests positioning them so that each is mounted far enough in front of a seating position that the angled light falls on the occupant's face, and spaced so that there is a fixture at about 45° to each side of him or her.
Thus the fixture to one side acts as a key light; the one on the other side acts as a fill. "We've had a great deal of success when we've been able to mount these fixtures in pairs, putting two in front of each participant," Darville explains. It helps that the light from these fixtures is diffuse, throwing almost as much light to the sides as to the front. That keeps the light pleasing, even in situations where the fixtures are not perfectly positioned for each person in the room.
"You have to light the people evenly," Darville says. "There should be no more than a 10:1 contrast between the lightest and darkest areas in the room – and no more than a 1.5 to 1 contrast between the overall illumination on one person's face and the next."
The color of video conferencing lighting is also important. Two criteria define the color provided by the lamps, color temperature measured in Kelvin (K) and Color Rendering Index (CRI). Video cameras work best with a color temperature between 3000 - 3500° K and a CRI of 80 or above. Even more important is color consistency.
It's important to note that color temperature does not describe the full spectrum of light and thus different types of fixtures of the same color temperature may produce visibly different colors (e.g. florescent and incandescent).
"Different color lighting really throws the cameras off," Darville explains. "You can mix in incandescent fixtures for decorative lighting purposes, but during your videoconference shut the decorative fixtures off."
You also need a sufficient lighting level. While modern cameras will perform well at brightnesses far below what you'd see in a studio, it still takes roughly 30-50 foot-candles on your participants' faces to produce clean images (300-500 Lux).
Another advantage of the Lutron fixtures is that they work well for meetings and classes as well as video. At first glance, they look like normal florescent fixtures. "Most people don't realize this is special lighting," Darville says.
2. Background lights
Another important consideration is the level of lighting on the wall or walls behind VTC participants.
If the background is too dark, it will throw off the iris in the camera and peoples' faces will 'bloom' and lose detail. If it's too bright, the iris will close and faces will darken. Taking the color of the wall coverings into account, there should be no more than a 1:2 ratio between the brightness of the faces and the background. The background should be uniform as well: avoid dark spots and bright areas.
On the subject of backgrounds, Darville suggests that various objects, artwork and logos can all work well – as long as they are stationary. "The technology is such that videoconferencing systems only refresh things that move. So if you keep the system too busy refreshing something that's moving unnecessarily, you will lose detail where it matters."
Everything said for the back wall will apply to side walls if they are visible in the picture. It's important to reiterate that lighting used on the back or side walls must be the same color as the main lighting. Thus if you use the Lutron 3500K VTC florescent fixtures, you must use fluorescent fixtures of about 3500K elsewhere in the room.
Darville suggests that windows always be shaded during a videoconference, preferably with blackout shades.
Unshaded windows will play havoc on the lighting ratios you carefully establish and introduce light of a very different color than your room lights. Partially shaded windows will cause problems as well.
"A particularly difficult window treatment is mini blinds," Darville says. "When the sun shines through mini-blinds, you get streaks of light across peoples' faces, and those faces show up as blobs to the camera."
Though it may not seem obvious, the furniture you choose can have a big effect on the image quality of your conference.
White or very light furniture will reflect too much light upward into people's faces, spoiling much of the effect that you get from special VTC fixtures. Medium tones are best: gray, tan or wood tables work well, if they have a matte finish.
Highly reflective furniture is worse, whether light or dark. A polished wood table can reflect glare from ceiling fixtures into people's faces or directly into the camera, as can stone or glass.
If you can't choose or change the furniture, try adding tablecloths or place mats to block unwanted reflections.
Be sure to consider the shapes of the tables you order. An oval or rectangular conference table all but ensures that some participants will not be seen when they turn toward a camera at the front of the room. A wedge-shaped table will solve the problem.
A well-designed room with the Lutron fixtures installed. Note that little or no glare comes back to the camera position from either the main lights or side wash lights (all of the fixtures are turned on in these photos). Note too how evenly the room and the faces are illuminated. There is contrast, but it's kept within the tolerances outlined in this article.
As you choose light fixtures, consider what the room will look like from the camera's point of view.
Standard florescent fixtures throw a great deal of glare toward the camera, and so the ceiling will register as a big bright area in any wide shots. That can be distracting and it will cause the camera's iris to close more than it should. The same is true of wall sconces and other bright sources of light that will show in the camera's view.
If you have florescent wall wash fixtures on your side walls, be sure they are designed and installed so you don't have bright spots showing up on camera. Finally, be sure your window coverings don't have light leaks visible to the camera.
"In summary," Darville says, "at least go after the basics. Light the peoples' faces from the front. Keep light from going directly into the camera. Make sure you always use fluorescent lamps of the same color temperature. Think about contrast. Light the back wall at least – the side walls if you can. You don't want any dark areas or too-bright surfaces. If the room has windows, deal with them appropriately."