In regard to estimation and costing of public lighting, which of the following should be adequate to provide v

Question

In regard to estimation and costing of public lighting, which of the following should be adequate to provide visibility that guarantees for the user the maximum safety and sufficient visual comfort?

Examoogle · Accepted Answer

The correct answer is Option B: Level of luminance. The level of luminance is the primary requirement for road lighting design as it directly determines the brightness perceived by the driver's eye. Providing an adequate level of luminance ensures that obstacles and road features are visible against the background, thereby guaranteeing safety and comfort for road users.

Step-by-Step Solution & Concepts:
The level of luminance is the primary requirement for road lighting design as it directly determines the brightness perceived by the driver's eye. Providing an adequate level of luminance ensures that obstacles and road features are visible against the background, thereby guaranteeing safety and comfort for road users.

Working Principle: Road lighting functions based on the principle of luminance contrast, where objects become visible when there is a luminance difference between the object and the road surface. By maintaining a specific luminance level, the contrast threshold of the human visual system is satisfied, allowing for the detection of hazards at safe distances.

Key Formulas: $L = \frac{ho 	imes E}{\pi}$ — relationship between luminance $L$, illuminance $E$, and reflectance $ho$ of the road surface; $	ext{Contrast} = \frac{L_{obj} - L_{bg}}{L_{bg}}$ — basic formula for visibility contrast

Key Points: Luminance is the measure of the light reflected from the road surface towards the eye.; Higher luminance levels reduce the reaction time of drivers in hazardous conditions.; Visibility depends on both the level of luminance and the uniformity of luminance.; Glare control and optical guidance are supplementary to ensure visual comfort.

Advantages: Reduced accident risk at night; Improved traffic flow and capacity

Disadvantages: High energy consumption; Potential for light pollution

Applications: Street lighting design; Highway illumination; Tunnel lighting

Additional Info: Luminance is measured in $cd/m^2$ (candelas per square meter).. While uniformity of luminance is important for avoiding visual 'patchiness', the absolute level of luminance is the fundamental requirement for the threshold of visibility.. Glare limitations refer to the restriction of disability and discomfort glare caused by luminaires.

Answer: B is correct — Level of luminance is the fundamental metric that dictates the visibility of road surfaces and objects for safe nocturnal driving.

Exam Tip: In illumination engineering exams, always distinguish between 'Illuminance' (light falling on a surface, measured in Lux) and 'Luminance' (light reflected/emitted towards the eye, measured in $cd/m^2$); road safety design is almost always governed by Luminance.

Examoogle · Answer

Option A: Limitations of glare

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Option C: Optical guidance

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Option D: Uniformity of luminance

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