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Street Lights

(A)   Factors Affecting Street lighting

        1)      Luminaries

•   High Pressure Sodium vapor lamps(HPSV)
•   Compact fluorescent lamp (CFL)
•   Light Emitting Diode (LED)

         2)      Pole to pole distance
         3)      Height of the pole
         4)      Overhang
         5)      Level of illumination(LUX)
         6)      Uniformity of luminaries
         7)      Dimming system         
8)      Automatic shutoff
9)      Power factor
         10)    Operation & maintenance

(B)    Advantages of Effective Energy-efficient Street Lighting

  • Uniformly light on roads of sidewalks
  • Reduced glare and improved visibility
  • Improved safety and security
  • Energy savings
  • Maintenance cost savings
  • Aesthetically pleasing atmosphere

(C)    Various features of Effective Energy-efficient Street Lighting Systems are

  1. Luminaires

    It is a complete unit consisting of a lamp, together with the parts designed to distribute the light, to position and protect the lamp, and to connect the lamp to the power supply.
    These are important to ensure luminaire efficiency and cutoff and glare control, to guarantee the right level of lighting

    Cutoff luminaire is recommended where the direction of maximum intensity may vary but below 65º. The principal advantage of the cutoff system is the reduction of glare.
    Semi-cutoff luminaire is recommended where the direction of maximum intensity may vary but is below 75º. The principal advantage of the semi-cutoff system is a greater flexibility in siting.

COMPARISON SHEET OF HPSV, CFL, LED

Fixture Parameters

HPSV

CFL

LED

Wattage

191

120

78

Lifespan(yrs)

2.7

3.9

5.7

Energy used(kwh)

1647

1267

683

Durability

Not Very Durable - glass or filament can break easily

Not Very Durable - glass can break easily

Very Durable - LEDs can handle jarring and bumping

Light output(3100 lumen)

190 watt

120-125 watt

78-80 watt

Switching

Instant

Takes time

Instant

Sensitivity

Yes

Yes

No

Source: www.designrecycleinc.com

LED street lights are preferred instead of high pressure sodium vapor (HPSV) or high pressure mercury vapor (HPMV)

Advantages:

  • Very longer life
  • Reduced maintenance costs due to long lifetimes
  • Do not contain toxic chemicals (e.g., mercury)
  • No warm up needed (no time delay to reach optimum brightness levels)
  • No production of ultraviolet light (which is what attracts insects)
  • Useful for directing light on specific areas, since they produce “directional” light -- light emitted in one direction, rather than a diffused glow
  • Can be dimmed (unlike CFLs), allowing for flexibility in controlling light levels
  • High color index, providing bright, true colors during night hours
  • No glare effect, reducing visual fatigue for both drivers and pedestrians
  1. Pole to pole distance

Spacing is the distance, measured along the center line of the road, between successive luminaires in an installation.
To preserve longitudinal uniformity, the space-height ratio should generally be greater than 3.

  1. Height of the pole

 It provides uniform light distribution, which improves appearance for safety and security. Also minimizes the number of poles, reducing energy and maintenance costs.
For very important routes with rapid and dense traffic recommended height is 9 to 10 meters,
For secondary roads with considerable traffic height recommended is 7.5 to 9 meters
For roads bordered by trees and for residential roads it should be less than 7.5 meters

  1. Overhang

Overhang is the horizontal distance between the center of a luminaire mounted on a bracket and the adjacent edge of a carriage way.
In general, overhang should not exceed one-fourth of the mounting height to avoid reduced visibility of curbs, obstacles, and footpaths.

Recommended levels of illumination in LUX for street lighting are:-

  • Important traffic routes carrying fast traffic should have 30 LUX

  • Main roads carrying mixed traffic like city main roads/streets should have 15 LUX

  • Secondary roads with considerable traffic like local traffic routes should maintain 8 LUX

  1. Uniformity of Luminaires

There should be uniformity in the LUX level of the light on the road, thus in order to maintain so there are four fundamental types of siting arrangements are recognized in street lighting. They are:

  • Single side arrangement.

Here all the luminaires are on one side of the road. This is recommended only when the width of the road is equal to or less than the mounting height.

  • Staggered arrangement

In this the luminaires are placed on either side of the road in a zigzag formation. This is recommended when the road width is 1 to 1.5 times that of the mounting height.

  • Opposite mounting

In this the luminaires are situated on either side of the road opposite to one another. This is advisable for road widths more than 1.5 times that of the mounting height.

  • Axial mounting

Here the luminaires are placed along the axis of the road. This is recommended for narrow roads the width of which does not exceed the mounting height.

  1. Dimming Systems

The use of dimming systems for street lighting is recommended when the supply voltage exceeds 220 V. This typically occurs between late night and early morning hours when traffic density is significantly reduced.
Automatic shutoff
Automatic shutoff in lighting should be provide as it saves energy and maintenance costs by turning lamps off when not needed.

  1. POWER FACTOR

Power factor of the lighting system is required to be near to unity.


Luminary

HPSV

CFL

LED

Power factor

0.77

0.65

0.9

Since LEDs provide highest power factor, thus can give high efficiency.

  1. Operation & Maintenance

Energy consumption for street lighting can be reduced by incorporating good maintenance practices such as:

  • Replacing defective lamps, accessories, and wires
  • Early rectification of cable faults
  • Making sure that cables are joined properly
  • Regular maintenance of service cabinet/fuse box to avoid loose connections
  • Regular cleaning of the luminaire cover to keep it free of dust/dirt and increase light output

A substantial amount of energy savings can also be achieved by installing mechanical/electronic timers and/or daylight sensors for turning street lights on and off.

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