sitelights
09-10-2001, 04:32 PM
If the trees are the focal point the trees should be uplighted. On trees with a large spreading canopy you may need to use multiple fixtures. We usually triangulate and use a fourth fixture for the trunk. An illuminated canopy without trunk lighting looks a bit strange. A tree with branches 25' from the ground can be illuminated with a single fixture with the appropriate lamp. A table of photometrics can be used to determine the necessary beam spread to match the diameter of the canopy. Example: an MR-16 20w 40 degree BAB lamp would create a circle of light about 20' across if the canopy started at 24' from the ground. These tables can be found in lamp catalogs and in some fixture catalogs. The 20w lamp would produce about 1 footcandle (fc) at 24'; a 50w EXN lamp would produce about 3 fc under the same circumstances. With multiple fixtures 20w lamps would be enough; a single fixture would need 50w if more than just a glow was desired.
If the focal point is beneath the trees (a walkway or a patio, etc.) then downlighting would be preferable. To avoid glare the downlights should have a regressed lamp or a shroud and should be aimed almost straight down. Again, photometric tables will guide you in your choice of lamps. Some trees, particularly "prunus" varieties, should not have screws driven into their bark and never use screws of copper or copper alloys in any tree.
Maintenance of tree-mounted downlights is always a problem since you must mount at least 24' above the ground to keep the light beam out of ordinary line-of-sight. Use stainless steel screws and staples; loop a cable tie through the staple and around the low voltage wire with enough slack to allow the wire to travel through the loop. Tree growth will otherwise engulf the cable or pull it taut enough to break. At a 24' working height you should always have an assistant to steady the ladder.
If the focal point is beneath the trees (a walkway or a patio, etc.) then downlighting would be preferable. To avoid glare the downlights should have a regressed lamp or a shroud and should be aimed almost straight down. Again, photometric tables will guide you in your choice of lamps. Some trees, particularly "prunus" varieties, should not have screws driven into their bark and never use screws of copper or copper alloys in any tree.
Maintenance of tree-mounted downlights is always a problem since you must mount at least 24' above the ground to keep the light beam out of ordinary line-of-sight. Use stainless steel screws and staples; loop a cable tie through the staple and around the low voltage wire with enough slack to allow the wire to travel through the loop. Tree growth will otherwise engulf the cable or pull it taut enough to break. At a 24' working height you should always have an assistant to steady the ladder.