How to Design efficient Street lighting-(Part-6)

(3) Light trespass:

• Light trespass is condition when spill (Unwanted or Unneeded) light from a streetlight or floodlight enters a window and illuminates an indoor area.

 How to Reduce Trespass

• Select luminaries, locations, and orientations to minimize spill light onto adjacent properties.
• Use well-shielded luminaries.
• Keep floodlight aiming angles low so that the entire beam falls within the intended lighted area.

 Difference between full cutoffs and fully shielded:

• The full cutoff has is luminaries that have no direct up light (no light emitted above horizontal) and 10% of light intensity between 80° and 90°.
• The term full cutoff is often substituted for the term fully shielded.
• The both terms are not equivalent. Fully shielded luminaires emit no direct up light, but have no limitation on the intensity in the region between 80° and 90°
• Luminaires that are full cutoff, cutoff, semi cutoff, and non cutoff , may also qualify as fully shielded.

• There is also a confusing assumption that a luminaire with a flat lens qualifies as a full cutoff luminaries. While this may be true or not in some Lighting Fixtures case.

• Fully shielded means, a lighting fixture constructed in such a manner that the bulb should be fully recessed into Fixture so that all light is directed downward below the horizontal.
• The fixture is angled so the lamp is not visible below the barrier (no light visible below the horizontal angle).

(G) Selection of Luminas:

(1) Types of Lighting Source

• Street Lights are mostly Low-pressure sodium (LPS), High-pressure sodium (HPS), Metal halide and Light emitting diodes (LED).
• LPS is very energy efficient but emits only a narrow spectrum of pumpkin-colored light that some find to be undesirable.
• LPS is an excellent choice for lighting near astronomical observatories and in some environmentally sensitive areas.
• HPS is commonly used for street lighting in many cities. Although it still emits an orange-colored light, its coloring is more “true to life” than that of LPS.
• Where it’s necessary to use white light, there are metal halide and LEDs.

• High-pressure sodium lamps should be used for expressways, main roads, secondary roads and branch roads.
• Low-power metal halide lamps should be used in mixed traffic roads for motor vehicles and pedestrians in residential areas.
• Metal halide lamps can be used for motor vehicle traffic, such as city centers and commercial centers, which require high color identification.
• Metal halide lamps, CFL lamps are used at Pedestrian streets in industrial areas, sidewalks in residential areas, and sidewalks on both sides of motorway traffic.
• LED streetlights are more durable, longer lasting, efficiency, dimmable capacity and cost effective than traditional lights.
• LED also enhances public safety by delivering superior visible light while providing the environmental advantage of using less energy.

 (2) Color Rendering Index (CRI):

• CRI Measures the ability of the artificial light to show or reproduce the colors of the road or objects on the road, relative to a natural light source.
• The natural light source (the sun) has CRI of 100. The higher
• This index the better the visibility will be. For all types of road CRI ≥ 70 is recommended.

(3) Efficacy

• At the low end LED efficacy starts at 70 lumens per watt (lm/W) and reaches as high as 150 lm/W.
• While the mean efficacy for outdoor area fixtures is slightly lower than common indoor fixtures such as troffers and linear lighting about 100 lm/W for area lights compared to about 110 lm/W for troffers and linear fixtures this difference is not significant. It may be the result of outdoor area lights requiring more precise luminous intensity distributions and other factors unique to outdoor lighting.

(4) Fixture Protection:

• When using sealed road lighting, the protection level of the light source cavity should not be lower than IP54.
• For roads and places with dangerous environmental pollution and heavy maintenance, the protection level of the light source cavity should not be lower than IP65.
• The degree of protection of the lamp electrical appliance cavity should not be lesser than IP43.
• Lamps with excellent corrosion resistance should be used in areas or places with high levels of corrosive gases such as acid and alkali in the air.

(H) Effective Road Lighting:

• Sufficient illumination.
• Good uniformity.
• No Glare.
• Low consumption.
• No Color Temperature abnormalities
• No Zebra effect
• Shielded lighting to ensure light is pointed downwards
•  Completely uniform illuminance.
• No requirement for over lighting to obtain sufficient average illumination.
• Absence of glare.
• Absence of low angle radiation that causes sky glow.
• Control of light trespass.
• High redundancy.