Runnels-Wells Group, LLC

McNeill, Mississippi

Plants with glossy leaf surfaces offer a reflective property that can create a dynamic effect when combined with overhead lighting.

Creative use of lighting has become increasingly popular in landscape design. Garden lighting offers extended evening hours for the enjoyment of outdoor environments, aesthetical enhancement of the landscape, human safety and comfort. This artifice of lighting has also increased the complexity of concepts used in the design of landscape lighting.

New technologies for implementing sophisticated landscape environments are not only dependent on lighting manufacturers' continued effort to give Landscape Contractors diversity when selecting a product, but also on the ability of the landscape designer to identify lighting needs that will compliment the visual effects of the darkened landscape.

Basic lighting techniques incorporate the use of design concepts such as focal points, depth-of-field perception and reflective patterns when creating special effects in the darkness of evening landscapes. Therefore, a lighting designer has many aspects to consider in the design stages of landscape lighting. One important aspect is the relation of luminance to the selected plant material. It is important that the lighting design approaches the same design line, texture, density and color that were originally intended for the landscape.

Considering Color in the Landscape

An effective technique for certain trees involves uplighting, such as this Live Oak on St. Charles Avenue in New Orleans.

Perception of color in the landscape follows the rule that red, yellow and orange jump out at you, where as greens, blues, and violets seem to fade away.

In the evening landscape, whites and silvers are reflective and showy, yet disappear during daylight hours. An explanation for this rule is that the visual light spectrum has wavelengths between 400 (violet) and 700 (red) nanometers. These wavelengths are often adsorbed by plant surfaces and a reduction of the overall luminance of the plant material occurs. We commonly refer to luminance as "the measurable brightness or reflective properties of an object in a landscape." The wavelength emitted by the light source and the color adsorbed by the plant will determine the color in which the plant appears in the landscape.

The color of a plant or object that is perceived by human visualization depends on the color reflected and not the color that is adsorbed. In general, when an object adsorbs all of the light rays it appears black and when all of the light rays are reflected an object appears white. The diversity found in the surface area and adsorption properties of plants result in a considerable change in reflective properties being measured. Appropriate illumination needed for a particular landscape area is often hard to determine without a general knowledge of plant material. Lamp criteria will be directly related to foliage density, morphology and the viewing distance.

Plants are also extremely sensitive to lighting due to physiological processes as well as aesthetical properties. Not only can lighting the landscape during the evening hours interrupt the photoperiodic responses of plants, but it can also change the plant's aesthetical presence in the landscape. Interruption of natural lighting conditions can effectively induce flowering of some plants and require groupings of herbaceous plants to appear inconsistent. It is also the question of Landscape Contractors whether or not these light breaks have an effect on the cold hardiness of plants.

Selecting Plants for Landscape Lighting

Shadows and highlights draw the eye to the aged trunk of this Ligustrium Japicium.

Important aspects of plant selection for lighting components in a landscape design include identifying the plant type, determining plant texture, density and color.

Evergreen trees and shrubs have a tendency to offer a silhouette appearance and consistent illumination year-round. Deciduous trees and shrubs show seasonal change, therefore illumination of these plants in the landscape changes drastically during seasonal transition and will often require lighting adjustments during periods of dormancy where foliage has experienced abscission from the plant.

Plant density is defined as open, medium or compact. Plants with an open density are often used to highlight plant structure, filter light and create patterns against walls and other surfaces. Plants with medium density are primarily used to conceal light sources and reflect light from glossy leaf surfaces. Finally, compact plants make suitable material for use as silhouettes against backlighted areas and as reflective borders along pathways.

The texture of a plant refers to the foliage. Fine, medium, and coarse textures provide variance in luminance. Surface areas of these textures vary and create many different reflections of light. The coloration of a plant will often change during seasonal transition. Seasonal changes such as successional status, flower and fruit production, and bark exposure as the plant matures can greatly change the adsorption of visual light. A plant may appear to be a perfect selection during its growing season and then become quite a nuisance during periods of dormancy. It is important that the lighting designer determine the overall aesthetical appearance of landscape design year-round.

Below is a short list of interesting plants that have a proven visual performance in landscape designs where lighting is used to enhance plant structure, form and texture.

Trees and shrubs with interesting foliage color:

This Prytania Street apartment building in New Orleans shows how to enhance the beauty of the architectural design through the use of a soft overhead lighting source, which is concealed above the doorways.

• Blue spruce (Picea pungens)

• Sweet bay magnolia (Magnolia virginiana)

• Russian Olive (Elaeagnus angustifolia)

• Southern magnolia (Magnolia grandiflora)

• Cherokee Chief dogwood (Cornus florida 'Cherokee Chief')

• Nellie Stevens holly (Ilex cornuta 'Nellie R. Stevens')

• China fir (Cunninghamia lanceolata)

• Japanese maple (Acer palmatum)

• Carolina silverbell (Halesia carolina)

• Ginkgo (Ginkgo biloba)

• Chinese pistachio (Pistachia chinensis)

• Red Maple (Acer rubrum 'Drummondii')

• Japanese cleyera (Ternstromia gymnanthera)

• Nandina (Nandina domestica)

• Leatherleaf mahonia (Mahonia bealei)

• Japanese aucuba (Aucuba japonica)

• Littleleaf boxwood (Buxus microphylla)

• Burford holly (Ilex cornuta 'Burfordii')

• Florida anise (Illicium floridanum)

• Fatsia (Fatsia japonica)

Trees with interesting trunks:

• Crape myrtle (Lagerstroemia indica)

• Yoshino cherry (Prunus yedoensis)

• Whitespire birch (Betula platyphylla var. japonica 'Whitespire')

• Lacebark pine (Pinus bungeana)

• River birch (Betula nigra)

• Lacebark elm (Ulmus parvifolia)

• Sycamore (Platanus occidentalis)

• Shagbark Hickory (Carya ovata)

• Paperbark maple (Acer griseum)

• Live Oak (Quercus virginiana)

• Hackberry (Celtis occidentalis)

• Honey Locust (Gleditsia triacanthos)

Columnar Specimens for Silhouette:

Overhead lighting from a pole lamp provides safe lighting for this walkway in the French Market. The diversity of the reflective properties of plants is well described in this photo.

• Yew podocarpus (Podocarpus macrophyllus)

• Arizona cypress (Cupressus arizonica)

• Skyrocket juniper (Juniperus scopulorum 'Skyrocket')

• Italian cypress (Cupressus sempervirens)

• Spartin juniper (Juniperus chinensis 'Spartan')

• Bradford pear (Pyrus calleryana 'Bradford')

Answering Important Questions

New Orleans French Market landscape architecture captures the interesting brilliance of plant form, textures, and color as well as luminance of water features and bronze sculpture.

Important decisions must be made with clients before the designers' preparation of the landscape lighting designs.

First, what is the intended use of the landscape lighting? To provide safety and security, aesthetical enhancement of plant material, create an ambiance of outdoor living space, or display focal points and special effects throughout the garden? These questions are not so easily answered and may change many times in the as built plan of the garden.

Second, budgeting of lighting maintenance could very well eliminate many plant selections. For example, trees and shrubs with high amounts of leaf litter will require increased maintenance of up lighting fixtures, and plants such as vines and groundcovers that often have increased meristematic tissue activity will require more pruning to prevent obstruction of the lighting source.

Finally, as the landscape matures there is often a need to make changes in the selection of lighting fixtures. Budgeting for the future maintenance and lighting improvements may require the designer to use plant material with slower growth rates or plants whose growth habits can be controlled through selective pruning techniques.

Low levels of lighting in the landscape will be sufficient in providing the perfect harmony between landscape plants and structures. With careful design and construction, nightscapes can and will result in a work of art for all who contribute to their planning.