Lamps for street lighting

Choose of lamps for street lighting

(i) The selection of luminaries according to its lighting distribution

· two way streets
· crowded streets and high way
· Crosses and intersection.

(ii) Type of lamps which are used for street lighting

(A) Low pressure sodium lamp.

law pressure sodium lamps are the best for:
· More sharpness vision.
· High speed response.
· Less discomfort glare.
· Obtain large brightness area at the same value.

Note:

The power used in high ways is usually:
-150 W for 12 m width street.
-200 W for 15 m width streets.

(B) High pressure sodium lamps

High pressure sodium lamps are the best for the crowded ways because it can transmitted the colours.

Note:
The power which is used in crowed ways is:
-150 W/12 m.
-250 or 400 W/15 m.

Calculation of street lighting:

Where:

F: total luminous flux of the lamp.

UF: utilization factor ranges from (0.2:0.6).

MF: maintenance factor (0.8:0.9).

L: space between the poles in meter.

W: width of the road in meter.

E: Average illumination over the working plane. (10 lux for Sub main streets and up to 30 lux for main streets).

Notes:
For primary initial design the street loading can be estimated according to the next table.




Illumination level for street for lighting and mounting height of lamps

Example for street lighting

For 300 meter road of width 12 meter, compute the luminaries spacing (L) for average illumination of E = 30 LUX using 250 watt high pressure sodium lamp of 25000 lumen (take uf = 0.33, Mf = 0.9, pole height 6 meter)

Solution:



So that, number of luminaires = 300/21 =15 luminaires

Note:

The best tilt angle ( 6) for maximum light utilization ranging from 10:15 degree

Methods of streets lighting design

(i) The factors which effect on the street lighting design

· Passing safety.
· Safety of people.
· The region which pass through the street.
· Type of street.
· Numbers of crimes, rubbers and security requirement.

(ii) The steps which must be known design street lighting

· Street profile.
· The average lighting of street surface.
· The degree of permanent glare.
· The rate of visible direction which must be find.
· The degree of required the lighting regulation.

Comparison between good and bad design of outdoor lighting

Below are bad and good examples of outdoor lighting. Lighting with high glare will have a bright ball of light around the fixture where as lighting that is well shielded, low glare, and with minimal spillage will appear with a smaller or ball of light. First we will look at some bad lighting examples, then some good.

Bad Lighting design Examples

6 Mile by Laurel Park Mall. Notice the large halos around the lamps. These are bright 400 watt HPS fixtures that have very high glare giving a harsh appearance, plus causing unnecessary stress and distraction to the eye . This problem could be significantly reduced by using shielded fixtures and/or reduced wattage.

Mobil gas station on NW corner of Merriman and I-96. Notice the bright balls of light under the canopy, indicating high glare.

Good Lighting design Examples

Livonia City Hall's parking lot on Farmington and 5 Mile. The area uses non-excessive flat glass shoe box fixtures rendering good visibility with low glare. Notice how halos are smaller compared to previous pictures and the parking lot is well lit. (Camera shows HPS brighter that the blue white Metal Halide fixtures in earlier photos).

Sunoco on SW corner of 6 Mile and Farmington. Although the fixtures are not shielded, they are recessed under the overall canopy, and because they are not overly bright, the station is well lit and does not have obtrusive glare. Because the fixtures are not glaring or at excessive levels, attention is not drawn away from the area or activity because of lighting.