When most people think of lighting they think, "Is there enough light in this room so that I can see what I'm doing?" While it is important to see what one is doing by meeting minimum illuminance levels on the work plane, it is also important to make the space visually pleasing. There are many different ways to make a space visually pleasing. Some tactics to make a space visually pleasing is to add cove lighting, backlight a picture, and have a spot light on a piece of artwork in the room. One of the more common tactics is to illuminate a wall. We can usually find an illuminated wall in a lobby behind the reception desk. The illumination of this wall adds a decorative touch to the space, but it also draws the viewer's attention to the reception desk. This is one tactic that is used to make sure that people who enter the space know where they need to go to check in or get information from. Another reason that one might decide to illuminate a wall is to make the space look larger than it really is. This helps people to feel less trapped and more comfortable in smaller spaces.
If a designer decides to illuminate a wall there are multiple ways that it can be done, but two of the most common ways to illuminate a wall are wall grazing and wall washing. Wall grazing picks up all minor imperfections (in even application of spackle, nails, cracks, etc.) on a wall, therefore it is only used when there is a texture on the wall. By wall grazing a textured wall one accentuates the material being used because the grazer creates shadows and highlights. A wall grazer creates shadows and highlights on a wall because the light fixture is located anywhere from 0' - 2' away from the wall that is being illuminated. By illuminating a wall with a wall washer, one can achieve even lighting across the surface. A wall washer can be used on a smooth surface because unlike a wall grazer a wall washer will not pick up any minor imperfections on the wall. A wall washer is usually located one-third of the height of the wall. Wall grazing and wall washing are two different methods that are used to illuminate a wall, but achieve the same goal very differently. This assignment compares the outcome of wall washing vs. wall grazing in a room that is 25' wide x 75' long x 24' high. For the purpose of this assignment we will be lighting the vertical wall that is 75' x 24'. To ensure that we look at a broad scope of luminaire options, I will be preforming three calculations for wall grazing and three calculations for wall washing. Each calculation will use a different lamp type so that it can be seen how the outcomes compare when the source is changed. For the wall washing calculations a linear fluorescent, an LED, and a metal halide lamp will be used, and for the wall grazing calculations a linear fluorescent, an LED, and a halogen lamp will be used. Below you will find the methods I used to perform these calculations, the results that I obtained as well as what was determined by these results. If you would like more specific details about each calculation that was performed you will be able to find that information in Appendix B. Examples of wall washing and wall grazing can be found in Appendix A. |
In order to compare the results of the calculations, it first has to be determined what will be kept constant. It is not easy to decide what should be kept constant for each scenario because the variables that are being changed vary so much already. If calculations were being preformed only with an LED lamp then it would be easier to have constant color temperatures, input watts, CRI values, etc., but the calculations are being preformed with different lamp types. Since different lamps are being used in each calculation it is difficult to keep those variables constant for two main reasons. The first is that each lamp type has different properties that are more common for that lamp type, for example a metal halide lamp consume more Watts than a fluorescent lamp, and a fluorescent lamp consumes more Watts than an LED does. The second is that the lighting industry is starting to shift towards LED luminaires. Since the LED technology has become so much better in the last few years, manufacturers are starting to shift all of their products to LEDs, and discontinuing older products that were using halogen, metal halide and fluorescent lamps. Since they are discontinuing these products it is harder to find IES files that are using these lamps to run the calculations.
Since it is difficult to keep the luminaire properties as constant variables, a new constant had to be determined. The next solution was to place the luminaires the same distance away from the wall. However, wall washers and wall grazers are not placed within the same distance from the wall to begin with. It was decided that while this is a variable that changes between the methods to illuminate the wall it would be a constant variable within each method. The wall grazers would be placed right against the wall, and the wall washers would be located at 8' (one-third of the height of the wall) from the wall. The next constant that was considered was the number of luminaires that would be used. The wall washer fixtures are closer to point sources so it was not difficult to keep the number of those fixtures constant, but wall grazing is achieved by using a constant run of luminaires along the length of the entire wall. Since each company manufactures the fixtures at different lengths it is harder to keep the number of fixtures constant for wall grazing. Since the main purpose is to create an even illumination across the surface of the wall I decided to focus on 6 main zones. The zones revolve around the average height of a person which is 5'. The breakdown of the zones and their heights can be seen below. |
The top two graphs above compare the input Watts with the the fixture type. This allows us to see that the metal halide lamp consumes approximately 7 times the amount of watts than the LED and linear fluorescent fixture. From the wall washer graph it would be assumed that LEDs consume the least aount of Watts, but as you can see from the wall grazer graph LEDs, may not always consume the least amount of Watts. The LED wall grazer consumes the second highest amount of Watts, but it also produces the greatest illuminance on the wall if tou look at the illuminance wall grazer graph.
As the calculations were performed, it became noticeable that the metal halide luminaire produced the highest illuminance values for the wall wash fixture while the LED produced the highest illuminacne values for the wall grazer fixture. While both of these produce the highest illuminance values in their respective categories they also create the brightest hot spot at the top of the wall. The hot spot is less noticeable with the metal halide fixture because there is a relatively smooth gradient across the surface of the wall. The LED wall grazer however does not have a smooth gradient when the illuminance values drop off therefore the hot spot on the top of the wall is more noticeable. A area of concern for all of these calculations is the spill light on the floor and adjacent side walls. Since I kept the fixtures in the same location and had approximately the same number of fixtures for each situation. There was no way to control where the light will be spilling onto the walls or the floor. |