Street lighting systems are becoming more necessary and important nowadays as night use of public roads has increased easily.
In order to have safer, comfortable, more convenient, efficient movement of vehicles and pedestrians at night time, street lighting or highway lighting is required along the road.
Street lighting should be planned appropriately, it should allow night traffic operations with maximum possible safety, comfort and convenience.
Street lighting should be planned in such a way that the driver should be able to see more clearly and explore all the important details of the driving environment.
Need for Street lightning:
- The main purpose of street lighting is to enable road users to see accurately and easily the carriageway and the immediate surroundings in darkness.
- Most road accidents occur at night and poor lighting is the main reason.
- Improved visibility at night through artificial lighting reduces stress on driving and ensures comfort.
- Vehicle drivers feel more confident driving under proper street lighting.
- With better lighting, traffic speed generally improves and traffic flow conditions improve.
- Highway lighting is especially important at intersections, bridge sites, level crossings and places where traffic movements are prohibited.
Types of Street Lighting:
Single side light system:
This system is extremely economical and suitable for narrow pavements for very light traffic.
Staggered light system:
This system is more suitable for wide pavement and light traffic conditions.
Central light system:
This system provides very effective lighting at low cost due to savings in luminaire support and electrical conductors.
It gives consistently well lighted on the road without interruption, but the pavement and bicycle path are comparatively dark.
Design Factors for Street Lighting:
1. Size, colour and brightness of the object:
The Night visibility depends on the size, color, and brightness of the object.
It is more important that there is sufficient color contrast between the object and its background so that an object can be detected on the road, hence visual performance during night driving depends on a factor called contrast.
Principle method of discernment as follows:
Discernment by silhouette:
It is barrier that may appear as a dark field against a bright background.
The brightness and consistency of the road pavement and crossing the roadway is important to enhance the discretion by silhouette.
Discernment by reverse silhouette:
It is an obstacle that can appear bright against a dark background.
This principle method is generally applied to areas adjacent to roadways and projections above the surface of the pavement to have greater visibility.
3. Drivers eye glare:
There are certain types of glare that cause serious effects on the driver’s visual performance.
Types of glare:
It is also known as a disability glare that develops from stray light, which damages visual efficiency due to reduced visual efficiency.
This type of glare can be minimized by increasing mounting height, moving the luminaire from the line of sight and increasing the brightness of the background.
It is also called discomfort glare that occurs because of ocular discomfort from a bright light source.
Such brightness can be reduced by increasing the height and background brightness, reducing the luminaire brightness.
The most common lamps commonly used for street lighting are sodium vapor lamps, tungsten filament lamps, mercury vapor lamps, and fluorescent lamps.
5. Lateral placement of lighting poles:
According to I.R.C, the road poles should be located with horizontal clearance from the pavement edge:
i. For roads with raised kerbs like urban roads, the minimum horizontal clearance is 03 m and it is desirable to have 0.6 m from the edge of the raised curb.
ii. For roads without raised kerb as rural roads, the minimum horizontal clearance is subject to 1.5 meters from the edge of the carriage and a minimum of 5 meters from the line of the center of the carriageway.
6. Layouts of lighting or arrangement of lamps:
Street lights can be arranged in a different system or methods as described below:
- Single Side Light System.
- Staggered light System.
- Central Light System.
- Contrast lighting.
- Combination of central, staggered and contrast lighting systems.
7. Luminaire distribution of light:
The luminaire distribution of light must be appropriate to obtain optimal use of the source of light or luminaire.
The distribution of light should be such that it covers the pavement between the kerbs.
The luminaire distribution of light should focus on the pavement and the surrounding area from 3 m to 5 m.
The distribution of light should be more specific or clear so that traffic signs and other objects on the road can be easily seen.
The distribution of light should be uniform, bright and the pavement should occupy more area.
8. Mounting height and overhang:
The height and overhang of the lamp from the pole is more important because the distribution of light, shadow, and brightness effects from street lamps depends on the height of the lamp and its overhang.
The height of the lamp varies from 6 meters to 9 meters. The increasing value of lamps is more preferred to important urban roads.
The lamp’s overhang from the pole provides better distribution of light on the pavement and enables less glare in the eyes of road users.
Spacing of Lamps for Street Lighting:
It should have closer spacing of lights, so that the road has suitable, better brightness and visibility during the night.
The spacing of light depends on the importance of highway or road.
By performing experiments, the normal distance is recommended to be from 35 m to 55 m for better brightness and visibility during the night for all types of roads.
The difference between pales on highways can be calculated from the following expression.
Lamp lumen X coeffient of utilization X maintenance factor / average flux X width of road.
Note that the maintenance factor is assumed to be 0.8 coefficient of utilization can be determined from the utilization coefficient charts.
Benefits of highway lighting:
1. Due to proper street lighting, police can do better patrol during the night and their work becomes easier and more manageable.
2. Increase in business in a city or town, areas during the night that would otherwise be completely uninhabited.
3. Architects and town planners have considered lighting as a major source for beautification of their projects.
4. Due to good street lighting, the accident rate during the night reduces significantly.
5. Illegal works on the streets and anti-social activities are definitely discouraged by better lighting techniques.
6. It gives a pleasant atmosphere at night.
Street lighting is an essential public service that provides a safe environment for night time travelers as well as pedestrians.
Proper use of street lighting can be considered as a protective method that provides economic and social benefits to the people.