A subcategory of exterior lighting, landscape lighting is distinctive in its goal of presenting a pleasing outdoor scene. While safety, security and use of space are important, aesthetics are key, as designers use light to tell a night-visual story within a living, growing environment.

With this bit of mystery surrounding landscape lighting, guidance can be valuable. In late 2023, the Illuminating Engineering Society published ANSI/IES RP-47-32, “Recommended Practice: Landscape Lighting.” This 77-page document provides guidance to the landscape lighting environment, design process and techniques, and equipment and methods.

Design

Identify project parameters and goals, including main viewing areas, focal points, traffic patterns and access, tasks, hours of use, occupant age, security issues, how the lighting should be controlled, and importance of minimizing light trespass, skyglow and glare. For example, a main viewing area might be from a deck or certain rooms.

Similar to indoor lighting, landscape lighting can use a layered design approach (task, ambient, accent) to highlight points of interest, set a mood and overall respect a sense of balance and unity across the visual scene. Points of interest may be as much as 10 times brighter than the grounds and three to five times brighter than secondary focal points. Some fill light can tie these points together within the field of view.

Darkness is as important as light here, as we are not seeking to turn night into day, but compose a scene. This requires careful attention to what must and must not be lit. A sense of depth can be cultivated by breaking the view into fore, middle and backgrounds, with progressively higher brightness on vertical surfaces toward the back. Depth and texture can be emphasized with luminaires that produce shadows.

Downlighting and uplighting can be accomplished by washing, grazing, cross-lighting, side-lighting, backlighting and silhouetting. RP-47 explores how to apply these techniques to numerous landscape lighting applications. One interesting technique is moonlighting, where luminaires are mounted in a tree to emit light through branches and leaves. A 4,100K light source with a very wide beam distribution can roughly mimic moonlight with a broad, soft light and patterns of shadows on the ground.

While 4,000K to 4,200K correlated color temperature luminaires are available, and 2,400K luminaires are available to imitate the warm glow of candlelight, many landscape lighting luminaires have a warm visual appearance at 2,700K to 3,000K. A 2,700K source is considered well suited to traditional architecture (stone and brick) and residential landscape lighting. The somewhat cooler 3,000K source is well matched for contemporary architecture and public spaces. RP-47 recommends a good color rendering index of 80+. Luminaires with color tuning can create striking scenes.

Installation

Installation is a close second to design in terms of project success. For existing landscaping, all installation should respect the existing plants, ensure the design will be preserved based on future plant growth and enable future ease of maintenance.

Wiring should be planned based on design requirements, voltage drop (lessened with LED, but still a concern) accounted for and all wiring concealed. The transformer should be where it does not interfere with aesthetics and is otherwise optimized for the wiring layout and maintenance accessibility. Luminaire positioning and aiming may need to be adjusted based on existing landscaping, and the commissioning process should ensure objectionable glare does not exist at any viewing angle. If luminaires are placed in trees, an arborist may need to be involved.

Quality assurance 

Commissioning can involve a daytime and nighttime review. Equipment placement and wiring connections should be checked during the day. At night, the team can see the design operate in its intended use and fine-tune it, ideally with the designer involved.

Maintenance

Maintenance is critical to ensuring design integrity, particularly given the challenges of outdoor environmental conditions and the constantly growing and shifting vegetation.

RP-47 recommends that the owner indicate or agree to maintenance practices during the design and prior to installation. Maintenance includes replacing failed components, cleaning luminaires, checking wiring for damage and adjusting the angle of luminaires. Considerations for future maintenance include typical plant growth, seasonal impacts, wildlife, expected traffic and vandalism potential. If the owner is unsure, they can commit to programmed maintenance. RP-47 suggests keeping the design simple, such as avoiding placing luminaires in trees, where the tree may grow around the luminaire and become damaged by it.

ANSI/IES RP-47-23 can be purchased at tinyurl.com/ycxzt6y2.