LED Street Light Replace Traditional Street Light Analysis

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LED Street Light Replace Traditional Street Light Analysis

1, Basic concepts of  Road

According to road using function,  the city road can be divided into two kinds. One is motorway for  vehicle using  and another one is pavement mainly  use for non-motor vehicles and pedestrian.

Motorway can be divided into Expressway and 3 grade road: Major Road, Collector Road, Local Road.

Express Way

Long distance, large traffic volume, service for fast vehicle. Having central reservation separate the traffic flow in opposite directions. Full control or portion control on the Exit and Entrance.

Major Road

Connect the main area of the city, separate the motorway and pavement. like 3 lanes or 4 lanes.



Collector Road

Combined with the main road to form the road network to distributing traffic.



Local Road

Connection Collector Road and residential areas



                                                         Urban Road Basic Profile Statistics

Road grade


Motor vehicle lanes


Non-motorized vehicles



Major road

Two- way 6 lanes



With Divider

Collector road

Two-way 4 lanes



With Divider

Local road

Two lanes







Note: 1. Generally lane is 3.5-meter-wide, some is 4-meter-wide

2. The divider include double yellow lines, iron fence, green belts, etc.


Basic concepts of lighting

Luminous Flux

The light source emits the sum of visible light per unit time . Symbol ΦLumen units(LM)

Express the unit of the power of light source, represent light source ability. the luminous flux indicates the radiated power of the human eye to see, as the function of the spectral radiant power of influence after the physical size of the luminous flux, in essence, use your eyes to measure radiation flux of light,with the light intensity of the radiation and the wavelength related.


Receive the lumoinous flux per unit area.Symbol E, Lux units (Lux)

It indicates the degree of the object to be lighted, 1 lux=1 lm/m2. A lux is 1 Lumen uniform illuminance on a 1 square meter area . Vertical illuminance is accepted as a standard flux, if oblique irradiation illuminance is decreased.

Average Road Surface Luminance 

Measure the data through  preset point on the road or calculate the average of  each point of illumination according to the relative  rules  of the CIE.

 Uniformity of Road Surface Luminance 

The ratio of the minimum illuminance and the average illuminance on the road


the intensity of light emitted from a surface per unit area in a given direction.Symbol L, units of candela / square meter (cd / m2)

Brightness is refers to the light (reflective) surface luminescence (reflective) the strength of physical quantities, namely, the luminous intensity on unit projection area

Longitudinal Uniformity of Road Surface  Luminance

The ratio  of the minimum brightness and the maximum brightness  in the center of the same lanes

Luminous Efficacy

The ratio of  total light flux emitted by the light source and electric power consumed. Symbol η, units of lumens per watt (lm / w)

Luminous efficiency is an important indicator to measure the light energy. Luminous efficiency with higher values indicating the ability to lighting equipment turn electrical energy into light  is stronger, that is in the case of providing the same brightness, the energy-saving lighting equipment is stronger; at the same power, the lighting fixtures is stronger, that the greater brightness.

 Power Factor

In AC circuits, the phase difference (Φ) cosine for voltage and current. Symbol cosΦ.In value, power factor is the ratio of active power and apparent power ,  cosΦ = P / S, P represents active, S indicates apparent power.Power factor determine the ratio of the effective power and reactive power.Higher Power factor, higher the effective power, the higher the utilization of electrical energy .

Color Temperature 

Represents the scale of light source color ,symbol Tc, unit K (Kelvin).Color Temperature  is defined by the blackbody, and the color of the light source emitted light hue blackbody radiation while at a temperature, at this time the blackbody temperature is called the color temperature.

 Color Rendering Index 

The extent of the original source of the object color rendering. Symbol Ra, range 0-100. It denotes a light source on the color capability of the object, the higher  CRI, the bettercolor.

Photometric Data

It means a light source (or lamps) light intensity distribution space in all directions.



National standards of lighting

Motor vehicle traffic road lighting should take the average surface brightness (or average surface illumination), surface brightness uniformity and vertical uniformity (or road illumination uniformity), glare limits, inductivity and the environment as  assessment index.


Motor vehicle traffic road lighting standard value


Luminance  Illumination Glare limitation Environment
average luminance (cd/m2 ) Total uniformitymin longitudinal uniformitymin Average Illumination(lx) Maintain value Uniformitymin The threshold incrementmax SRmin
I Express road Major road 1.5/2.0 0.4 0.75 20/30 0.4 10 0.5
II Collector road 0.75/1.0 0.4 0.5 10/15 0.35 10 0.5
III Local road 0.5/0.75 0.4 8/10 0.3 15


  1. The average illuminance only for asphalt pavement in the form. If the Department of cement concrete pavement, the average luminance value may be reduced by about 30%. Appendix A of this standard average luminance coefficient can be determined given the same average brightness pavement, asphalt pavement and cement concrete pavement were average illuminance required.
  2. Maintaining the average luminance calculation or maintenance of the road should be based on the average illumination light sources, lighting protection and wipe cycle, determined in accordance with Appendix B of this standard maintenance factor.
  3. The values in the form apply only to dry road .
  4. The left side of the average luminance and the average luminance of each level is given two tranches road standard values, “/” for the low value of the right side is the high-end value in the form.

Sidewalk  road lighting should take the average surface illumination, pavement minimum illumination and vertical illumination as  assessment index

Sidewalk road lighting standard value

The night traffic Area Average Illumination Eav(lx) Minimum Illumination Emin (lx) Minimum vertical illuminanceEvmin (lx)
Large traffic Commercial district 20 7.5 4
Residential area 10 3 2
Medium traffic Commercial district 15 5 3
Residential area 7.5 1.5 1.5
Little traffic Commercial district 10 3 2
Residential area 5 1 1


The minimum vertical illuminance is the center line of the road at a height of 1.5m from the road, in both directions perpendicular to the plane of the road axis of minimum illumination

Lighting parameters comparison

According to the planning and design of urban road lighting,  generally major road use high pressure sodium lamp 400w, collector road 250w, branch 150w,major road,  collector road and voeux Road use 150w.


High pressure sodium lights and LED street lights parameter comparison

Performance parameters High pressure sodium light LED street light
Power (w) 150 250 400 78 126 172
Luminous efficiency (lm / w) 100 112 120 97 100 102
Luminous flux 15000 28000 48000 7500 12600 17400
Color Temperature (K) 1900 2000 2000 5000 5000 5000
Power factor 0.44 0.44 0.44 >0.92 >0.92 >0.92
CRI 23 23 23 70 70 70
Lifespan  4000 4000 50000 50000 50000  4000


Light Parameter Reference Philips SON-T high-pressure sodium lamps, LED street lights LED general reference. High pressure sodium lamp is a gas discharge lamp ballasts need to maintain a stable voltage, high pressure sodium lamp power including the power source, power ballasts, transformers, power lines and power loss, the whole lamp power is generally 1.2 times the power of the light source. Therefore, the entire sodium lamp 150w power consumption is 180w, 250w sodium lamp power consumption is the 300w, 400w high pressure sodium lamp whole power consumption is 480w

Road lighting planning

 Conventional road planning standard

Road grade Pole height /m Pole spacing/m Arm length/m Lamps elevation/o Pole mrgins/m
Major road 12 35 1.5 15 0.5
Collector road 10 30 1.5 15 0.5
Local road 8 25 1.5 15 0.5


1 Arm should not exceed 1/4 of the height of the installation, generally 1.5 meters long, and 0.5 meters and 2 meters long

2 lamps elevation ≤15 °, there are 0 °, 10 °, 12 °.

3 pole margin refers to the horizontal distance from the road edge stone, generally 0.5 m, 1 meter, 2 meters ,etc.


Pattern of lighting

Conventional lighting arrangement can be divided into five basic ways that is  one-sided arrangement, bilateral staggered, bilaterally symmetrical arrangement, the central and lateral suspension disposed symmetrically arranged. When using conventional lighting methods, it should be selected based on the road cross section forms, width and lighting requirements, and  meet the following requirements:1992 11 11

(a)                                      (b)                                  (c)                                       (d)                                   (e)


(a):one-sided arrangement

(b):bilateral staggered

(c) :bilaterally symmetrical arrangement

(d): the central symmetrical arrangement

(e):lateral suspension arrangement


Pole height and spacing

The relationship between the type of light distribution、arrangement and Installation height、spacing

Light distribution type cut-off luminaire semi-cut-off luminaire non-cut-off luminaire
Arrangementmethod InstallHeightH(m) SpacingS(m) InstallHeightH(m) SpacingS(m) InstallHeightH(m) SpacingS(m)
one-sided arrangement H≥1Weff S≤3H H≥1.2 Weff S≤3.5H H≥1.4 Weff S≤4H
bilateral staggered H≥0.7 Weff S≤3H H≥0.8 Weff S≤3.5H H≥0.9 Weff S≤4H
bilaterally symmetrical arrangement H≥0.5 Weff S≤3H H≥0.6 Weff S≤3.5H H≥0.7 Weff S≤4H


Weff is road surface effective width (m),LED street light are semi-cut-off luminaire.


Effective Road Width

theory width for road lighting design , which is the actual width of the road, the cantilever length and lighting fixture Arrangement and so on. When the lamp unilateral Arrangement, effective road width minus a cantilevered length of the actual road width. When the lamp with bilateral (including staggered relative) Arrangement, the effective width of the actual road lane minus two cantilevered length. When the lamp in the middle of double-width belt-way car use is not centrally symmetric Arrangement, the effective width of the road is the actual width of the road.

Cut-off Luminaire

The direction of the maximum intensity of lamps and  lamps down vertical axis Angle between 0 ° ~ 65 °,the maximum permissible value of light intensity angle of 90 ° and 80 ° diagonal direction were 10cd / 1000lm and 30cd / 1000lm . And regardless of the size of the luminous flux, the maximum light intensity in the 90 ° diagonal direction shall not exceed 1000cd.

Semi-cut-off Luminaire

The direction of the maximum intensity of lamps and  lamps down vertical axis Angle between 0 ° ~ 75 °,the maximum permissible value of light intensity angle of 90 ° and 80 ° diagonal direction were 50cd / 1000lm and 100cd / 1000lm . And regardless of the size of the luminous flux, the maximum light intensity in the 90 ° diagonal direction shall not exceed 1000cd.

Non-cut-off Luminaire

The direction of maximum intensity of the lamp is not limited, the maximum light intensity 90 ° diagonal direction shall not exceed 1000cd

Feasibility Analysis


Lighting efficiency

 High pressure sodium lamp  360 ° omni-directional light, only 45% to 55% luminous flux irradiated to the road, the second optical design optical loss of 10%, 10% glass transparent varnish damage, so the actual exposure to the pavement flux only 35 to 45%. In 250w high pressure sodium lamp, for example, the initial luminous flux 28000 actual exposure to the pavement luminous 11200 lm. LED lights directional light, directional light output is good, after the adoption of the second optical design is still 85% of the luminous flux reach the road. In 126w LED lights, for example, the initial luminous flux 12600 lm, irradiated ground flux 10710 lm.

2016 7 4

lighting  effect

High pressure sodium lamp with high light efficiency, generally above 100 lm/w, LED street  lighting is 95 lm/w.But the actual luminous efficiency, LED street lamp is higher than the high-pressure sodium lamp. Such as the initial luminous efficiency 112 lm / w, the whole lamp power 280w, pavement effective luminous flux 11200 lm, the actual luminous efficiency 40 lm / w in  250w high pressure sodium lamp.the initial luminous efficiency 100 lm / w, the whole lamp power 126w, pavement effective luminous flux 10710 lm, the actual luminous efficiency 80 lm / w in 126w LED street lamp.

CRI ( color rendering index )

Narrow spectrum of high pressure sodium lamp, color rendering index is low, generally only 23-33, feel dark on road surface , poor color reproduction on the object itself, light irradiation object obvious distortion, low pressure sodium lamp color rendering assistance can only help drivers and pedestrians detect road conditions, and can not help pedestrians clearly identified. LED color rendering index is high, generally 75-80
Close to the sun, so that the irradiated object color more
Vivid, color rendering is more real, more able to reflect the color of the object itself. LED high color rendering help drivers and pedestrians do not identify the target, the road looks brighter, feel more comfortable, safer and better traffic conditions at the same brightness pavement.



Color Temperature

High pressure sodium lamp spectrum relatively concentrated in yellow, the color temperature is relatively low, only 2300-3200K, dark yellow, prone to hypnotic mood. LED color temperature is higher,  generally is above 3500-5500K ,with warm colors and cool colors color temperature, pavement bright and comfortable, to meet a variety of lighting applications for color temperature, LED higher than high pressure sodium lamp the in actual lighting effect .

Light distribution curve

 High pressure sodium lamp 360 ° omni-directional light, the reflector  through the secondary optical design, spot is oval, easy to form a dark band and zebra effect, a lower degree of road illumination uniformity.


LED lights directional light, favorable light distribution curve design and control, LED street light distribution curve is symmetrical Batwing, rectangular spot, help improve the average intensity of street lighting and illumination uniformity, control the generation of glare.



High pressure sodium lamp                                                            LED street light



High pressure sodium lamp is a gas discharge lamp, lamp life is greatly affected by voltage fluctuations, the design life of 20,000 hours, light fades serious, light fades 30% after 1000 hours, the actual life is 4000-6000 hours, replaced once a year. LED lights use of advanced technology systems integration, ingenious cooling structure, and application of polymer materials, life of 50,000 hours and 10,000 after the maintenance of the initial luminous flux of 95%, 50,000 hours to maintain 70% of the initial luminous flux.

Repair and maintenance 

High pressure sodium lamp is convenient maintenance, mainly to replace the lamp and ballast bulb average 1-year replacement, ballast average of 2 to 3 years to replace one, lower maintenance costs. LED lights integrated modular technology, maintenance is simple, easy to maintain, just a screwdriver to disassembly lamps, if bad driving, driving on the exchange; if an LED light source module damage, damage the module to change without replace the whole lamp, which saves cost and easy to operate. In summary, the two-year warranty LED lights instead of traditional lights have the advantage, life expectancy has increased more than 10 times, saving more than 60%, the overall illumination increased about 70%, low maintenance cost and easy maintenance. Qinhuangdao Hebei Avenue with a total length of about 10 kilometers an example, the number of two-way street dual lamp 462, a total of 924 lamp, the main pole 12 meters high 400W + 30W high pressure sodium lamps totaling 462 199.8 kilowatts / hour, sidewalk auxiliary poles 10 meters high 250W + 30W high pressure sodium lamp, a total of 462 130 kilowatts / hour, light summer time is short, lighting time long winter annual average daily lighting 10 hours, according to commercial electricity 1.2 yuan a day, electricity 3957.6 yuan, 1.45 million yuan per year, LED lights replace 120W and 78W combination lamp combination lamp, according to the above criteria is 55 kW / h and 35 kW / h of electricity 1080 yuan per day, the annual electricity 473,000 yuan, the annual electricity savings of 977,000 yuan. 1.954 million yuan for two years saving street lamp market price of 500 yuan, the annual average of 1,000 yuan to replace the second annual procurement costs 925,000 yuan. Two years procurement costs 1.85 million yuan. Mechanical street maintenance fee per year labor costs of about 30 million, two-year $ 600,000 to replace the LED road
Two lights save about 450 yuan. Replacing the LED lights will cost about 3.7 million yuan two years, saving an average of 80 million, LED lamp actual life  is longer than warranty,and save more costs.


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