What is Lighting Quality?

a guest post by Lisa J. Reed, Lighting Designer

We often talk about how high-quality lighting can promote productivity, comfort, and well-being. Now this concept has been incorporated into a credit in the newest version of LEED.

We often talk about how high-quality lighting can promote productivity, comfort, and well-being. Now this concept has been incorporated into a credit in the newest version of LEED.

According to LEED v4, lighting quality is five things. In the new LEED, a lighting quality credit can be achieved by employing four of eight optional strategies.

Lighting quality is:

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  1. Low glare
    Luminance of below 2500 cd/m2 at high viewing angles between 45 and 90 degrees above nadir. This means using cutoff fixtures or those without glare. Lamps need to be recessed into the light fixtures to achieve this, not hanging out at the ceiling plane.
  2. Good color rendering
    The LEED version of “good” color rendering is a CRI of 80 or higher. I submit that in today’s world, we can do better. Try for 90+.
  3. Long life
    75% of your installed lighting will have to last 24,000 hours or longer. Many linear fluorescent lamps will qualify. Most LED lamps will qualify. Halogen and CFL sources will not.
  4. Indirect lighting
    Only 25% of the installed lighting load for regularly occupied spaces can be direct only. Use direct/indirect fixtures or indirect lighting. People love indirect lighting. Now we get LEED points for it too.
  5. Good surface reflectances
    1. These two options can be used to achieve comfortable and energy efficient reflectances within a space. One is for the reflectance of ceiling, walls, and floor to be fairly high. White paint is more reflective than black paint. When surface reflectance is high, less energy is required, because light bounces around the space instead of being absorbed by dark colored surfaces. LEED v4 requires a minimum weighted average reflectance of 85% for ceilings, 60% for walls, and 25% for floors.
    2. Furniture finishes are important for lighting reflectance and contrast, too. Where furniture is included, work surfaces should have a minimum 45% reflectance (this probably rules out mahogany desktops), and movable partitions need to be 50% reflective. Light surfaces all around.
  6. Even illumination
    1. We experience spaces three dimensionally, so the illuminance ratio of the task to the walls around us is important to minimize eye fatigue. Used in conjunction with the good reflectance requirements, the maximum ratio of walls to work surface for 75% of the regularly occupied area must be 1:10. This means that the light falling onto the work surface can be no more than 10x the amount of light falling onto the walls.
    2. Similarly, the maximum ratio of ceiling illuminance to work surface illuminance for 75% of regularly occupied spaces is required to be 1:10. Sitting in a completely dark room with just a task light will probably not meet these requirements.

While this may fall short of a complete and thorough description of lighting quality, it is a step in the right direction, and I applaud USGBC for addressing the issues of quality and not just energy consumption without regard for its effect on people.

Lisa J Reed photo - Lighting Blog

Lisa J. Reed has been attracted to lighting (like a moth to a flame) for 20+ years. She is the Founding Principal at Envision Lighting Design, LLC in St. Louis, where she designs, teaches, and writes about architectural lighting.


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