Uplighting is the most commonly used garden lighting technique, for shrub borders and large trees especially. By uplighting trees, one exploits a unique opportunity to add vertical emphasis and drama in a garden lighting scheme. Trees with an open habit allow light to fully display the branch structure, while the contrast of colour between subjects can be emphasised. The light coloured bark of a silver birch, the coppery stems of Prunus serrula Tai-Haku, the golden fern-like foliage of Gleditsia triacanthos "Sunburst" or the subtle green and white striped bark of Acer pensylvanicum are all examples of good lighting subjects.
For trees with dense canopies and darker foliage, uplighting rarely works well on its own. Uplighting through the central branch structure and crosslighting the canopy from a second source is one alternative; really dense canopies, such as conifers, can only be lit from outside. Where there are several trees in a view, avoid lighting them uniformly (unless you are lighting an avenue). Light some from the front and others from the side to provide contrast.
Lighting a house wall to silhouette a tree in front is an interesting effect if the tree has an open structure. Alternatively a spotlight in front can project the shadow of a tree onto the wall behind, a good way of using a small acer to create a big effect in a newly planted garden. Try to “fit” the lamp beam to the tree shape to avoid wastage of light and energy by studying the lamp beam diameter and the pool of light it provides at a given distance. To uplight small to medium size trees, use one or more a tungsten halogen lamps of 50 - 75 watts and a beam angle to suit the tree - 24 degrees for a slender silver birch, 60 degrees for a weeping tree and 36 degrees for most tree shapes in between.
Trees can be good lighting platforms in relation to shrub borders, as well as a way of lighting terraces, driveways, paths, steps and seating areas. A favourite technique is "moonlighting" down from low power lights fixed in a tree to shadow the lower branches and foliage onto the ground below. This provides a subtle, dappled lighting effect over a tree seat and is also a creative way of integrating the lawn into the lighting scene or lighting a path or drive in a rural garden. For moonlighting, or if you are spotlighting a feature from a tree, use a dedicated tree spotlight on a tree or surface-mount, with a glare shield to hide the light source from view and a brown or “bronze textured” powder-coat finish which blends well with tree bark. You can find more advice on designing lighting for trees and on choosing the right lighting products at places like Lighting for Gardens.