Roadway lighting Roadway lighting is one of the most common exterior lighting applications. provides illumination for drivers, pedestrians and associated users. is a key element in the development of many urban and rural areas. requires large investment in energy use

Roadway lighting Methods for specifying efficient products and maintaining aesthetically pleasing installations provide : energy efficiency benefits, potential economic benefits (by increased commercial activity and tourism). (by increased commercial activity and tourism). The science and art of roadway lighting : new and more efficient light sources, improved luminaires and controls, new standards of roadway lighting practices

PURPOSE OF ROADWAY LIGHTING Promotion of safety by providing quick, accurate, and comfortable vision for drivers or motorists and pedestrians. Promotion of safety by providing quick, accurate, and comfortable vision for drivers or motorists and pedestrians. Improvement of traffic flow by providing light, beyond that provided by vehicle lights. This aids drivers in orienting themselves, and delineating roadway lighting geometries and obstructions, which reduce vehicular accidents. Improvement of traffic flow by providing light, beyond that provided by vehicle lights. This aids drivers in orienting themselves, and delineating roadway lighting geometries and obstructions, which reduce vehicular accidents. Provision of adequate illumination visibility for safe vehicle operation in long underpasses and tunnels. Provision of adequate illumination visibility for safe vehicle operation in long underpasses and tunnels. Help prevent street crimes. Help prevent street crimes. Increase commerce within the premises. Increase commerce within the premises.

ROADWAY LIGHTING EQUIPMENT Roadway lighting equipment can be grouped into three general components : Optical System : light source, reflector, refractor and housing. Optical System : light source, reflector, refractor and housing. Electrical System : ballast, wiring, photoelectric control and other minor components. Electrical System : ballast, wiring, photoelectric control and other minor components. Structural System : the mounting brackets, pole and foundation supporting the luminaire and associated equipment. Structural System : the mounting brackets, pole and foundation supporting the luminaire and associated equipment.

Light Sources for Roadway Lighting Light sources determine the visual quality, economy, efficiency, and energy conservation aspects of the illumination system. Light sources determine the visual quality, economy, efficiency, and energy conservation aspects of the illumination system. The factors affect the cost and effectiveness of installing, operating, and maintaining the light: The factors affect the cost and effectiveness of installing, operating, and maintaining the light: + the efficiency of a lamp in converting electrical energy to light, + the ability of the lamp to maintain its light output over the course of the lamp life, + the length of the lamp life, + the color of the light, + the distribution of the light.

CHARACTERISTICS OF COMMON LIGHT SOURCES Color Characteristics Color Characteristics Color Rendering Color Rendering Index (CRI). Correlated Color Temperature (CCT). Lamp Lumen Depreciation (LLD). Lamp Lumen Depreciation (LLD). Average Rated Life Average Rated Life

Color Rendering Index (CRI) Color Rendering Index The measure of the degree of color shift, which objects undergo when illuminated by the light source, as compared with the color of those same objects when illuminated by a reference source of comparable color temperature. The CRI uses filament light as a base for 100 and the warm white fluorescent for 50. Values for common light sources vary from about 20 to 99. The higher the number, the better the color rendering or color appearance (less color shift or distortion occurs).

Correlated Color Temperature (CCT) Correlated Color Temperature The absolute temperature (in Kelvin) of a blackbody radiator whose chromaticity nearly resembles that of the light source. The chromaticity of general lighting lamps, measured in Kelvin (K) falls in the range 2200 to 7500K. The CCT indicates visual warmth or coolness. At 4000K and above, the chromaticity usually described as cool. Around 3500K, sources have a neutral appearance. At 3000K and below, the lighting effect is judged to be warm.

CHARACTERISTICS OF COMMON LIGHT SOURCES (cont.) CHARACTERISTICS OF COMMON LIGHT SOURCES (cont.) Lamp Lumen Depreciation (LLD) Lamp Lumen Depreciation (LLD) The fractional loss of lamp light output in lumens at rated operating conditions that progressively occurs during lamp operation. Lamps produces less light as it ages and near end of life. LLD is caused by lamp coating and electrode filament deterioration. Average Rated Life. The life value assigned to a particular type lamp. It is commonly statistically determined estimate of average or of median operational life. Rated life is the point at which 50% of a large group of lamps is expected to fail under standard or specified test conditions.

LIGHT SOURCES FOR ROADWAY LIGHTING Most roadway lighting installations use one of three types of high­ intensity discharge (HID) lamps : Mercury Vapor (MV) lamps, Metal Halide (MH) lamps, High Pressure Sodium (HPS) lamps, (the most commonly used). (the most commonly used).

Lamp Identification In present practice,the designation commonly starts with the following letter: "H" for mercury vapor "M" for metal halide "S" for high pressure sodium This is followed usually by designations that identify the electrical characteristics of the lamp and ballast; the size and shape of the lamp; the wattage and color of the lamp. Color temperature, base type and mounting (burning) position designations may also be added.

Mercury Vapor Lamps Mercury Vapor Lamp is an HID lamp in which the major portion of the light is produced by radiation from mercury operating at a partial pressure in excess of 105Pa (# 1atm).

Mercury Vapor Lamps Construction and Operation. The outer glass envelope of the mercury lamp is made of a borosilicate hard glass, which is needed to withstand the high operating temperature of the lamp. The outer glass envelope of the mercury lamp is made of a borosilicate hard glass, which is needed to withstand the high operating temperature of the lamp. This outer glass shell absorbs much of the UV radiation emitted by the mercury arc. This outer glass shell absorbs much of the UV radiation emitted by the mercury arc. Some mercury vapor lamps have a self­ extinguishing feature to shut the lamp off if the outer glass bulb is broken, preventing exposure to ultraviolet radiation. Some mercury vapor lamps have a self­ extinguishing feature to shut the lamp off if the outer glass bulb is broken, preventing exposure to ultraviolet radiation.

Mercury Vapor Lamps

Metal Halide Lamps Metal Halide Lamp is an HID lamp in which the major portion of the light is produced by radiation of metal halides and their products of dissociation ­ possibly in combination with metallic vapors such as mercury.

Metal Halide Lamps Similar in construction to mercury lamps, metal halide lamps provide white light at higher efficacies and with better lumen maintenance than mercury sources (due to metal halides in the arc tube). Metal halides may feature a phosphor coating that converts the excess UV into visible light, improving the lamp's CRI rating in the process.

Metal Halide Lamps

High­pressure Sodium Lamps In HPS Lamps, light is produced by radiation from sodium vapor operating at a partial pressure There exist clear and diffuse­coated lamps.

High­pressure Sodium Lamps The outer glass envelope of a high pressure sodium lamp is made of a borosilicate hard glass, which is needed to withstand the high operating temperature of the lamp. The arc discharge is produced by a mixture of xenon and a sodium­mercury amalgam in the polycrystalline alumina arc tube.

High­pressure Sodium Lamps

HPS with Starter

Characteristics of Lamps for Roadway Lighting TypeRatingwInitialOutputlmEfficacylm/WCRIColorTemp. o K ColorAppearanceWarm-upTimeminRestrikeTimeminAve.Op.Hours MV40to100012,000to13,00030­6515­205600to7000Coolblue­green3­5510,000to16,000 MH32to1,50019,500to26,30070­12560­963000to6000 white light 2­10153,000to20,000 HPS35to100023,000to28,50060­14022­652100to2200yellow­orange3­53­410,000to24,000

SELECTION OF LIGHTING EQUIPMENT FOR ROADWAY LIGHTING AFFECTING FACTORS lamp lumen output. lamp lumen output. lamp life. lamp life. lamp lumen depreciation. lamp lumen depreciation. luminaire lamp distribution. luminaire lamp distribution. lamp restrike time. lamp restrike time. lamp color. lamp color. surrounding or ambient temperature. surrounding or ambient temperature. physical size of lamp and luminaire. physical size of lamp and luminaire. physical durability of lamp and luminaire. physical durability of lamp and luminaire. cost. cost.

LAMP INSTALLATION POSITION The output of some type of lamps is sensitive to lamp position. Choose the right lamp for the intended position for installation. The output of some type of lamps is sensitive to lamp position. Choose the right lamp for the intended position for installation. Manufacturers classify their products into 3 categories: Manufacturers classify their products into 3 categories: Vertical base­up (VBU) Vertical base­down (VBD) Horizontal position

Type of Light SourcesAdvantagesDisadvantages Mercury vapor lamps · Long life · Good luminaire light control · Small luminaire size · Long restrike time · High lumen depreciation · Poor lamp efficacy Metal halide lamps · High CRI · High lamp efficacy · Good luminaire light control · Small luminaire size · Long restrike time · High lumen depreciation · Poor lamp efficacy (photopic efficiency) (photopic efficiency) High pressure sodium lamps · Long lamp life · High lamp efficacy · Good luminaire light control · Small luminaire size · Minimal lumen depreciation · Low CRI · Restrike time required

LIGHT LOSS FACTOR LIGHT LOSS FACTOR (Maintenance Factor) LIGHT LOSS FACTOR (Maintenance Factor) The light loss factor (LLF) is the ratio of the illuminance when it reaches its lower level just before corrective action is taken as compared to the initial level. The light loss factor (LLF) is the ratio of the illuminance when it reaches its lower level just before corrective action is taken as compared to the initial level. This is estimated by a study of This is estimated by a study of the conditions under which the system will operate, the atmospheric conditions, the frequency of cleaning, and the depreciation of the lighting effect. The LLF are divided into two categories The LLF are divided into two categoriesunrecoverablerecoverable.

LIGHT LOSS FACTOR Unrecoverable Light Loss Factor. attributed to equipment and site conditions that cannot be changed with normal maintenance procedure. (temperature factor, line voltage factor, ballast factor, luminaire surface depreciation, equipment operating factor, and the lamp positioning factors). (temperature factor, line voltage factor, ballast factor, luminaire surface depreciation, equipment operating factor, and the lamp positioning factors). Recoverable Light Loss Factor. can be changed by regular scheduled maintenance. (cleaning and relamping luminaires, cleaning and painting room surfaces, lamp lumen depreciation, luminaire dirt depreciation, and lamp burnouts).

LIGHT LOSS FACTOR Calculations for Total Light Loss Factor. The total light loss factor is simply the product of all the individual factors that contribute to the loss of light. The total light loss factor is simply the product of all the individual factors that contribute to the loss of light. Where factors are not known, or applicable, they are assumed to be unity (or may be omitted in the calculation). Where factors are not known, or applicable, they are assumed to be unity (or may be omitted in the calculation).