The layout of road lighting should be based on nature of the road (brightness & uniformity requirement) and the lighting fixtures
(power, lumen output, beam angle, etc). We need to take a comprehensive consideration on the function, aesthetics and the
investment cost in order to achieve the best street lighting design. This article is sharing with you the basic and advanced knowledge,
as well as how our LED street lights fulfil the requirement of different lighting projects.
Installation Parameters of Street Light Fixture
Generally, the road lighting fixtures are mounted to the protruding arm of the light pole. Let’s firstly have a look at how will we describe the installation height,
cantilever length, elevation angle and other parameters.
1. Installation Height of Street Lamp (h)
It refers to the vertical distance from the center of the lamp to road surface. The installation height falls within the range of 6 to 14 meters
depending on the width of the road. In general, the greater the installation height, the fewer the glare, the better the uniformity, and the wider
the spacing between the poles. However, it also means that we will need the luminaries having higher power and lumen output.
In the past few decades, the height of the pole gradually increased. This is due to the improvement of the lighting efficiency, says the energy
efficiency of LED lights raised from 50 to 130 lm/W. Increasing the pole height not only achieve better uniformity, but it is more economical and beautiful.
Majority of the light poles are having the height of 12 meters or more, and multiple lights will be mount to a high mast pole for the highway interchange.
Despite this, sometimes we use very short pole for aesthetic reasons, such as the use of ceiling-mounted garden lights or street lamps
(with decorative light poles) in residential area.
2. Cantilever Length of Luminaries (Oh)
It refers to the horizontal distance from the edge of road to the center of light source. Increasing the cantilever length can also increase
the brightness of road surface; however, the brightness of sidewalks will be decreased in this case. This parameter affects the lux level on the lane and
pavement. If the cantilever length of the lamp post is fixed, we will need to apply asymmetric optics on the street lights to balance the difference.
3. Lamp Elevation Angle (θ)
It indicates the angle between the opening (surface) of the luminary and the horizontal plane. By increasing the elevation angle of the luminary on the light pole,
the light can project farther; however, it also aggregates the glare which irritates the pedestrian and drivers. In general, the elevation angle is controlled within 15°.
4. Street Light Spacing
As its name suggested, it refers to the distance between the adjacent lamp post. To decide the best street lighting installation spacing, we need to consider
the positioning of the pole, size of road grid (distance between adjacent crosswalk), terrain of the road as well as the surrounding buildings.
Generally speaking, it would be more economical to use the lighting fixtures with high luminous, high installation height and weight installation spacing.
To get the better lighting design and layout, the street should be:
i) easy or convenient to access and maintain.
ii) tall enough to avoid the street light is hit by vehicles, and obstructs the growth of trees.
iii) less glare (or even anti-glare).
iv) bright enough to also light up the traffic signs and signals.
v) appearance (to embellish the street).