Road Lighting Design is another fascinating field for newbie Civil Engineers. Please read this interesting blog to understand Road Lighting Design Process, key design constraints, software’s, etc.
Why Road Lighting is Required?
Road Lights are provided to illuminate the road and associated infrastructure such as footway, cycle track, controlled & controlled crossings, etc so that all road users can safely travel in dark hours.
Road Light cannot entirely replicate the same daylight, but road lighting design helps designers to develop a lighting model to eliminate dark spots, provide a clear view of the road and associated infrastructure and provide a desirable minimum illumination for all road users. Following are the Key roles that Road Lights play:
- Eliminate the Dark Spots and Illuminate the Road and associated Infrastructure.
- Illuminated Road Sign and ADS Signs assist drivers to make an informed decision.
- Minimise the risk of accident in dark hours.
- Discourage vandalism and crime in dark hours and low traffic environment.
Key Factor to consider for Street Lighting Design
The position of Lighting Columns and the level of illumination from each column should be made consistent so the drivers and other road users view a uniform level of brightness along the road. Uneven illumination can generate a blind spot for drivers and pose a severe road user risk.
Limit the Glare
A sudden glare (disability glare) and or a discomfort glare create a visual obstruction to the drivers and may lead to a serious road accident. Disability glare creates a black when the driver suddenly sees the light and move the eyes away from it. That’s why it very important to minimise the suddenly illuminated spots and sudden dark spots along the road.
Discomfort glare doesn’t come from sudden illumination. It comes uneven illumination, which means when there are spots where a very high level of illumination or bright spots are provided and then it is combined with a low level of illumination spots.
This creates a blurred image and low illuminated object because the eyelid fails to absorb the lower illuminated object immediately after seeing a higher illuminated object.
Adequate Contrast Sensitivity
Illumination makes road and associated infrastructure brighter as compare to the dark surrounding. it works very well along rural highways, but in the case of urban streets, dark surroundings are replaced by building and flashy glass office buildings.
As a result, the contrast level goes down and drivers don’t receive that level of contrast illumination. That’s why it’s very important to consider the surrounding land use pattern while developing the road lighting design and 3D model.
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Key Steps of Road Lighting Design:
Illumination Level depends on the point where it is measured, the height of that point from the road and the angular position of the lamp. Please see the formula below:
Ep = I cos2y / h2
Ep = Illimitation at a point
h = height of that point
Y = Angle of Illumination
I = Intensity of Illumination
Angle of Luminaire
Luminaire angles are split into two categories:
The throw angle is measured from the lamp along the road as shown in the picture.
The spread angle is measured from the lamp across the road as shown in the picture.
Variation of Street Lighting with Type of Road
Road Lighting varies with the road types. This means, for a high-speed motorway, Road Lightings are designed considering a different set of constraints than a low-speed road.
Constraints of the high-speed road for Road Lighting Design:
- High-speed and high traffic volume
- Hard Central Median such as concrete barrier or steel barrier
- Access & Exit through grade-separated junction only
- Advance Directional signs are placed
Constraints of Low-speed Urban Road Lighting Design:
- Low-speed traffic environment
- Traffic Calming Places
- Heavy pedestrian volume
- On-street Parking
- Taxi Bays and Frequent Bus Stops
- High Street Shopping Areas
The constraint of Low-speed traffic in Residential environment
- Low-speed Residential Roads
- Moderate pedestrian movement
- Bus Stops with or without bays
- School Zones with traffic measures
Lighting Pole Arrangement over the Column
For low speed urban single carriageway road, single-sided columns with frequent interval (8-10m) are provided. The spacing between poles is made consistent to provide uniform illumination.
Double-Sided columns are used for a dual carriageway road where lighting poles are places at the central median. In this case, double-sided columns hold lanterns for both side of the
Road Illumination Calculation Process
Road illumination is calculated using Lumen’s method as shown below:
E = n x N x Cou x MFx OL / A
A= Road Surface Area
OL = Illumination Level
N = Number of Lantern (1 for lighting columns placed on one side, 2 for both side of a carriageway)
n = number of lanterns in a lighting column (1 for single-sided and 2 for double-sided lanterns)
Cou = Utilization Coefficient
Road Lighting Design Software’s
There are many robust lighting design software’s to develop road lighting models and they come with a variety of options to address site conditions, constraints, and many other factors.
Please read this blog for details:
Use of BIM in Street Light Design
BIM Model provides a huge benefit when it comes to quality and accuracy of the design model and for lighting model, it adds further benefit such as linking to GIS (Geographic Information system) of power cables, voltage drops, photometric data and other parameters to the main control system for maintenance purposes.
To understand the advantages of BIM, please read this blog for details:
Hope this blog gives you some clarity on Road Lighting Design. Please feel free to like, share and comments.
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