Hi, it’s Robert Hawkins and I’m here on behalf of the TLA Applications Team to talk about best practices and share my “rules of thumb” for how to successfully graze, wash, and flood in your next project.

Basically, all three describe ways to light up a whole vertical surface, but all three have very different results and parameters to ensure success.  You can think of each as the result of the application of different setbacks along with different optics tailored to that setback.

While outlining the content for this post, Ryan Stewart asked me to share my “rules of thumb” for each technique. Here you go Ryan…

Bob’s Rules of thumb for lighting a vertical surface

1. Grazing only applies to closest to surface illumination.
2. Wall washing can start anywhere from 12” from the surface to much further, depending on the height of the surface to be illuminated and how much setback you have available.
   • Consider how far up the wall you want light to start.
   • Find a balance sometimes between how close to ceiling to start, vs how far down a surface you need to illuminate.
   • Dependent on the optics of the fixture utilized.
3. Flood lighting can only occur from much further from the surface (see further discussion below).

What is grazing?

Grazing results from the application of very narrow beam light sources from the closest distance to the intended surface. Grazing brings out the texture of the surface the most of all three techniques.

This can be good…as shown in the ledger stone installation below that creates a strong visual statement wall in a commercial elevator lobby. Note that the ledger stone represents deliberate texture where the grazing accentuates the difference in geometric surface elevation and plays on the contrast between light and shadow.

Or this can be bad… like in the image from our office below. Here you can see the result of bad drywall texture and bad lighting happening to good people.

When the surface is smooth it is more difficult for any light to be reflected to the eye. Think polished marble. VERY difficult to get a return off this material surface as it requires vast amounts of incident light.

Calculation of grazing is very difficult as the cosine of the incident angle falls off very rapidly as you leave the source. Best practice here is to take out your graph paper and Sharpie and do the math.

Footcandles at a surface = Intensity (candela) to the point (from the fixture), times the cosine of the incident angle, divided by the distance squared from source to surface.  

Horizontal illuminance:

Cosine function:

Vertical illuminance:

Grazing provides very little defined, calculated incident footcandles as a result once you get any distance from the source.

1. Graze: Bob’s rules of thumb for grazing

1. Best implemented with a continuous source, but individual units can be used as well.
2. They would need to be quite close together (an old-style system basically used par lamps 6” o.c to illuminate the marble wall mentioned above).

Let’s take a closer look at an example.

Center of optics 3” from a 9’ wall.  At 4’ down the wall, the incident angle is already 86.5 degrees with a cosine value of .06.   One can see why we don’t show much calculated fc there already, at .06 times the incident candlepower and then dividing by roughly 16 again for the distance. Defined incident footcandles are then .00375 times the intensity at that angle.

All fine from a calculation perspective showing not much light, but there is light there to catch textured surfaces and other items that are not parallel to the wall surface. Those not-parallel items then can “catch” the light with incident angles much closer to 0.

Below, here’s an example of grazing from our friends at Selux featuring an organically shaped wall and using M-Series LED with the A5 lens to highlight variances in the wall and to pull out dimensional aspects.

So grazing is a great way to bring out texture if desired, and the worst way to hide bad texture.  If there are to be items with significant depth sticking off the wall, it’s easy to get a bad result from not hitting the fronts of those items, but only their tops.

Think corporate lettering. This application would be best to address with washing.

2. Wash: What is wall washing?

Wall washing starts out with a further setback to the surface. Distinct distributions of light are designed for this purpose. A relatively tight, asymmetric beam in and out of the wall, with peak candlepower aimed toward the wall. This, along with some good side-side throw tends to define a wall washer. The source can take the form of downlights, with special reflectors, spaced close enough together that the wall gets smoothly illuminated below where the scallops join. The reflector attempts to minimize this high scallop and the close spacing is needed to ensure the best results highest on the wall.

Typically, a 1/1 – 1.5/1 spacing to setback ratio is used for these styles, sometimes stretching to 2/1. This results in many fixtures in a row, near the surface to be lit.  Single wall wash downlights do not really accomplish much, they need their friends to really be effective.

A linear, continuous source can be utilized as well. No scallops at all here, just the fade at the top, depending on setback. This can range from 6” to several feet depending on wall height. Both styles can be recessed, surface or pendant mounted.

Bob’s rules of thumb for wall washing

1. Lighting source can be downlights or continuous linear source with fade at the top depending on setback.
2. For individual units, typical spacing to setback ratio of 1/1 – 1.5/1 but may go as high as 2/1.
3. Sources can be recessed, surface, or pendant mounted.

Below, look at this example below of a focal artwork wall using Selux’s M-Series LED with the A2 lens to create a focal point by highlighting artwork. You can read more from Selux here in their Application Guide.

And this brings us to technique #3: Floodlighting…

3. Flood: Effective floodlighting

Floodlighting the surface is the most uniform way to illuminate a vertical surface. This also hides or minimizes texture.

Here is the same wall from our grazing photo above now evenly or flat lit:

What a difference!

Compared to the other two techniques, floodlighting requires more setback and then wider distribution of light source (hence “flood”). We often use floodlighting outdoors where setbacks can be greater, without affecting the space occupants with direct glare (since they are not normally present).

Floodlighting can use fewer sources of higher output to achieve similar average fc results as the previous methods. Floodlighting usually allows for complete top to bottom lighting without the scalloping seen in the recessed wall washing.

When applying this technique indoors, lighting the complete surface is typically handled by multiple sources on, say, a track system that can be aimed independently from each other. The track can be used for accent lighting as well, another discussion. Whereas outdoors, the source is often is turned upside down lighting from the bottom up.  Same discussion, just upside down.

Bob’s rules of thumb for floodlighting

1. Spacing can exceed the setback for flood lighting by several times depending on the optics and lumen package used.
2. Think 3-4 times setback from the surface.

If you have any questions on the information presented in this post, or would like to discuss an upcoming project with TLA’s team of experts, send me an email at rhawkins@thelightingagency.com