Luminaires and the Sound of Silence

Dec 9, 2019
Luminaires and the Sound of Silence

The design of the modern office has created unintended consequences for acoustic control. Lighting can help fix that

By Dirk Zylstra and Francois Renaud

In recent years, office spaces have undergone a comprehensive design reformation that reflects how we think about work. Our approach to work has been revolutionized by technology and generational change. Companies that want to be understood as progressive are increasingly using office and public places as a narrative vehicle for corporate brand and identity. Office design is increasingly becoming an efficient way to highlight corporate culture to the outside world, but it can also be a powerful tool for employee attraction and retention.

The trend in office design has long been toward open-office environments, but now we see an acceleration toward designing for collaboration, creativity and innovation. Rows of cubicles have been replaced by inviting, engaging and comfortable commercial spaces, where home and health are built into the environment. Work spaces are equally being influenced by “wellness” and “biophilic” design with the onset of LEED and WELL certification that value both the users of the space as well as the greater environment.

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As more and more millennials enter the workforce, these modern office trends are being quickly embraced and valued. Collaborative spaces have now become the new norm and are critical for generating team-spirit and morale at work. This trend is often exemplified by office ping-pong tables, espresso machines or organic groceries in the breakroom, but kidding aside, you would be hard pressed to find a Fortune 500 company that is not embracing this way of thinking. In many ways this evolution in office design has become emblematic of a generational changing of the guard.

New trends in office design have coincided with the LED revolution, and both have been a huge opportunity for the lighting, architecture and design communities. But there are challenges. One of the downsides of contemporary office design is the unforeseen effects of noise, poor acoustic control and lack of privacy that can affect productivity in the workplace.

Modern office environments present acoustic challenges due to design choices about physical layout, elimination of sound-absorbing elements while, at the same time, emphasizing materials that exacerbate the situation. Some common architectural elements like unfinished ceilings and fewer closed offices can significantly reduce the amount of acoustic-controlling elements in the environment. Likewise, a trend toward more and larger windows provides more hard and reverberating surfaces. Another design culprit is the trend towards exposed concrete surfaces—especially floors without carpets. Above all, the movement to ban the dreaded cube-farm from the modern office landscape has been great for communication and collaboration but has put a serious dent in the ability to concentrate.

It is obvious that an open-office design leads both literally and figuratively to the opening up of communication that is synonymous with dynamic enterprises. Most office workers fluidly cycle between the need for collaborative interaction and concentrated solo work, and herein lies the problem. A typical open office will generate noise levels of 60-65dB while focused, concentrated work requires a level significantly lower at 40-55dB. Furthermore, typical office workforces are more-orless split between individual workers and interactive workers who can spend over 60% of their time working collaboratively.

Workplace well-being requires maintaining a healthy physical and mental state, in both your environment and while interacting with colleagues. Already environmental noise from office equipment can be an acoustic burden, but the unwanted noise from people’s voices is the biggest challenge to creating and maintaining well-being in an office environment. Worse, the Lombard effect is the tendency of people to increase their speaking volume to compensate for noisy environments, thus ever-escalating the noise level in public spaces. Current science tells us that we have a bandwidth capacity to process only 1.6 human voices at any given time, and anymore becomes added noise. Hypertension, impaired cognition and general lack of concentration are all results of a poor acoustic environment. In addition, office and public spaces require a certain level of speech privacy for both productivity and legal reasons. This being the case, it is not surprising that an inordinate number of millennial office workers have taken matters into their own hands with the use of sound cancelling headphones.

So how can the lighting design community help address this issue? Unlike other office elements, lighting is generally out of the direct visual field in both offices and public spaces. At the same time, lighting is perfectly positioned to help control acoustics, making it a great design opportunity for fixture and lighting designers alike.

As lighting people, it is interesting to compare the basic physical concepts of acoustical control with those of lighting. We can visualize sound in the same way we do lighting. Sound is wavebased and, as such, has direction and intensity, travels over distance and fades with time. Sound is also affected by the physical environment through reflection, transmission, absorption and diffraction. The principles are basic, but like lighting, it gets complicated quickly and requires a more in-depth understanding. Frequency or pitch ranges from 20-20,000 Hz where the lower the number the deeper the sound. For lighting folks, we can compare this to CCT and for reference human speech is between 250-8,000 Hz. At the same time, you can compare loudness or intensity to lumens. The unit of measure for intensity is decibels (dB) where a whisper measures 25dB and a loud vehicle is 90-110dB, which can create discomfort, a bit like too many lumens can be glary.

Similar to the lighting industry, the world of acoustics has some basics measurements used to characterize acoustic absorption performance. The most common measure used to rate the acoustical properties is NRC (Noise Reduction Coefficient), which is often included in specifications of ceiling tiles, office dividers, wall panels, and now, lighting fixtures. The NRC value of a surface simply denotes its ability to absorb or reflect sound, and this coefficient is an average of the absorption of frequencies of 250, 500, 1,000 and 2,000 Hz. In this sense, NRC is like CRI in that it’s an average measure. Like two different 80 CRI sources can render differently, two products with the same NRC each might perform very differently for a specific application.

NRC of 1 is considered perfect sound absorption (like an open window) while NRC of 0 is a perfect reflector. Although we use NRC to rate products, this is not ideal for objects, because the actual NRC will depend on the application of the objects in a space. Like a light fixture may have an impressive amount of delivered lumens, it may not be enough for a very large space. The same goes for sound absorbing.

The Sabin count and NRC are often confused, but really, they work hand in hand. The Sabin count is the total of all absorption coefficients in the room. The higher the NRC values and quantity of soundabsorbing materials, the higher the Sabin count will be. Higher Sabins will lower background noise and offer a more controlled acoustic environment, because there is a reduction in sound waves reflecting in an environment. Simply put, the best way to control acoustics is to avoid reflection of sound.

When sound is persistent and reflected in a space, it is referred to as reverberation. When there are many reflections of sound, there is a notable decay as these sound waves get absorbed over time. This is most noticeable when the sound source stops, but the reflections continue, decreasing in amplitude, until they disappear. Although both are results of reflected sound, Reverberation (Hellllloooooo…) should not be confused with echo (Hello, hello, hello…). Reverberation creates noise, so to create a good sound environment, we want to reduce the reverberation time, or the time for a reflected sound to fade away. Like lighting has standard levels of illumination based on tasks, there are recommended practices that exist for reverberation time of various environments, and it is recommended to consult an acoustician for specific guidelines.

If the goal is to reduce reverberation time, then as lighting folks, what you need to know are the basic ABCs of acoustics. Absorb sound energy and reduce reflection. Block sound-using barriers to prevent straight line travel. And in some cases, Cover noise by using background sound. Lighting designers already know how to do this, since it is all about reflection, transmission, refraction and diffusion.

As lighting designers and lighting fixture designers, we have an opportunity to fill a void of sound-absorbing material in an unobtrusive, and even, elegant manner. The goal of the open-office design is to break down barriers, not create problems. Since lighting installed in the ceiling space and on walls is out of the direct visual field, there is an opportunity to add back some sound-absorbing material, while improving the overall aesthetic. In fact, the proximity to walls and ceilings will help the sound-absorbing effect, since sound will have the tendency to get trapped between the sound-absorbing surfaces and the building structure. At the same time, lighting fixture designers have been designing with fabrics for many years and this new approach to sound-absorbing provides many new creative opportunities. At the recent lighting shows, we have seen many companies jumping on this bandwagon and for good reason.

There are many approaches and technical solutions to integrating sound-absorbing into lighting fixtures, but not all solutions make great lighting. In terms of materials that will absorb sound there are a wide range of felts, fabrics, foams, or pulps. The bigger challenge is structurally integrating these materials in a way that the luminaire design is effective, firstly as a lighting fixture and secondly, as a sound-absorbing device. For effective sound-absorbing, the goal is to maximize the surface area, but this is not always easy when you are designing elegant lighting solutions. Another issue we have run into is the required amount of sound-absorbing material often outnumbers the required number of lighting fixtures to correctly illuminate a space. In this respect we find the most effective designs have been those with multiple layers of sound-absorbing material that provide sound traps that exponentially increase a luminaire’s sound-absorbing

Like in lighting, there are often wild claims regarding sound-absorbing performance. It is a good idea to look for fixtures that come with accredited lab tests measuring the sound absorption coefficients (NRC or SAA) but more importantly, it is important to review the way a product has been tested. Does the test scenario reflect the normal usage of that product, or is it simply trying to maximize sound-absorbing performance by maximizing surface area during testing? It makes no sense to have fixture spacing in a test that is unrealistic from a cost or lighting distribution point of view.

For critical projects there might be a need for hiring a professional acoustician who acts in a similar way to that of a lighting designer. Just like complex photometric calculations, acoustic studies can prove essential on larger architectural projects. There are many ways to achieve effective illumination in an open-office environment, and likewise, type, quantity and placement to maximize sound-absorbing elements is a complicated equation. That said, a good rule-of-thumb is more absorbing surfaces means reduced reverberation time, and due to trends in modern office design, you will probably never have too many sound-absorbing lighting fixtures.

This article is based on a presentation delivered at LEDucation 2019.