How Plants Direct the Approach to Lighting Them April 11, 2001 The size and shape of a plant directs our approach to lighting it. Plants with a narrow, upright shape and dense branching best express their texture and shape when lit by a grazing light. Some yews, for example, have a stiff upright shape; when they are pruned to maintain that shape, lighting fixtures can be placed close to the edge of the tree, bringing out the rough texture of their branching habit. The upright shape allows light to reach the tree top. Use a lamp with a narrow beam spread on upright trees, especially on tall palms. Trees with a more pyramidal shape, such as many redwoods, are best lit with fixtures moved back from the edge of the tree. Optimum distance varies -- from a few feet to 10 or 20 feet -- with the angle of the tree's overall shape as well as with the tree's height. Plants that have a rounded form with dense leaf overlap and thick leaf structure benefit from a wall wash technique. Lights placed under the canopy are typically wasted because the leaf overlap is too dense to allow light to filter up into the canopy. Moving fixtures out away from the canopy, as shown in the accompanying illustration, accentuates the shape of the tree. Remember that as you move the fixture away from the edge of the leaves, the effect of texture will be diminished. When selecting lamp wattage, remember to consider the effect of the reflectance value of a plant's leaves. It's also important to consider the "finish" of the leaves -- are they matte or specular -- because those factors affect the preferred aiming angle of the fixture as well as lamp wattage. To capture the full effect of trees that have a rounded shape with medium to open leaf overlap and translucent leaves, place light fixtures under the tree canopy. This filters light up through the branches, accentuating the tree shape and enhancing the three-dimensional qualities of the tree. Small trees with a canopy width of 5 to 15 feet require two to four fixtures. Trees with canopy widths from 15 to 50 feet may require 5, 10, or more fixtures -- depending on the size and shape of the specimen at maturity. With careful placement and attention to a tree's structure, a small number of fixtures may be used on a large tree. This creates a dramatic effect on the tree, because parts of the tree will be left dark. Generally, though, when a small number of lights are used, the result is a tree that looks disfigured. An exception to locating lights directly under the canopy applies when rounded, open-type trees have interest at the outer edge of the canopy. The crape myrtle (Lagerstroemia indica) for example, produces long conical flowers at the ends of branches; it has an open form with medium-sized leaves. Locating fixtures outside the canopy edge to light the flowers still allows light to filter through the canopy. Lights encircling the tree, as shown in the diagram, provide depth and fullness. Moving the fixtures out to the canopy edge provides accenting light on the beautiful flowers when the tree is in bloom and full, balanced light for the tree when it is not in bloom. When trees are close to a wall, fewer fixtures may be needed because the canopy size has been reduced. Consider washing or grazing the trunk softly with one or more of the lights to tie the tree to the ground. The side of the trunk you light depends upon the direction (or directions) from which the tree is viewed and the effect you are attempting to create. Trunk lighting techniques include side lighting to create crisp edges, silhouetting the trunk against a light surface beyond, and front lighting for detail and color. When the tree produces branches close to the ground, fixtures should he placed farther from the canopy in order to completely light the tree from the ground to the top. The angle can be relatively flat -- about 45 degrees from vertical -- because the tree will block glare for viewers on the opposite side of the tree. Plants that start branching a foot or more above the ground, however, need a steep aiming angle -- one no more than 35 degrees from vertical -- to avoid creating glare and to minimize lighting fixture surface brightness. When other plants or objects block the view of these fixtures, the angle may be more horizontal. Trees or shrubs that are dense and have leaves down to ground level often serve as a secondary focal plant in a lighting plan and create a bridge between two larger specimen trees. Often these occur in a border and will be viewed basically from one direction. In this case, the light should he located back away from the plant. A relatively horizontal aiming angle is acceptable because the plant itself shields the lamp brightness from creating glare. February 1989, Architectural Lighting Magazine