SEMLEDLight
LED lighting solution provider,Top experts in thermal material

LED Lighting Solutions

Street lighting Design

Outdoor Street Lighting Solutions

Program Overview

Sunnyvale is the city that in the second phase of assessing the feasibility of replacing the current high-pressure sodium (HPS) streetlights with light emitting diode (LED) luminaires. The first phase of this evaluation compared several competitive products against a set of criteria, choosing three of them for further evaluation. The second phase assessment involved the installation of these three products on Fremont Avenue between Hollenbeck and Mary Avenues. A total of six units per product were installed on twin-arm poles. Pole spacing for Vendors A, B and D of the monitored luminaires measured 143 feet apart. Pole spacing for Vendor C measured 137 feet. All monitored luminaires had a mounting height of 31 feet 6 inches. Field-testing was designed to determine if the new LED technology meets the Standard Practice approach for designing a roadway lighting system, meeting ANSI/IENSA RP-8-00 Roadway Standards with an emphasis on pedestrian and bicyclist safety. (IENSA is the Illuminating Engineering Society of North America).

Sunnyvale was chose to evaluate LEDs Type III distribution with full cutoff luminaires. LED streetlight performance was evaluated in four areas: Lighting Assessment in conformance with the ANSI/IESNA RP-8-00 Standards, Electrical Energy Use, Safety and Environmental, and Light Pollution.

Technology

An estimated 94% of roadway lighting in the U.S. is High-Intensity Discharge (HID) lamps and59% of those are HPS lamps. The introduction of LED streetlights has gained momentum over the years as a viable replacement for HID lights such as HPS streetlights because of their low energy usage, long predicted lifetime, and reduction in maintenance cost. LEDs also provide improving light quality that enhances road safety. Initial LED cost is higher than HPS, but reduced energy use and lower maintenance costs are a strong argument in favor of LEDs.

An LED is a semi-conducting device that produces light when an electrical current flows through it. It consists of a chip of semi-conducting material treated to create a structure called a p-n (positive-negative) junction. Current flows from the n-side (cathode) to the p-side (anode) when the barrier voltage inherent to the semiconductor materials and the various dopants used in the fabrication of the LED is exceeded. Since very little heat is created, and the voltages and current are relatively small, the resulting emission of photons is efficient compared to the power input.

The atomic characteristics of these materials determine the color (frequency) and efficiency of a device. Today, the standard white LED uses a blue LED that acts as a stimulator for its phosphor packaging material. These phosphors are the key to the broad spectrum of light emitted commonly called white light.

Current LED technology has the potential to provide significant electricity savings for streetlights.

As will be discussed in this report, depending on lighting luminaire design and how the systems are deployed in the field, an energy savings of 33 to 66 % can be realized.

Outdoor Street Lighting SolutionsAdvantages::

Substantial energy savings.

Reduced maintenance and operational costs.

Estimated luminaire life of 50,000 hours.

Light output can be directed and controlled.

Improve light quality for improved visibility and safety.

Project Objectives

Safety

Environmental Aspects

Energy savings

Conformance with ANSI/IESNA RP-8-00 roadway lighting standards    

Economic performance.

Safety is a primary concern for the City, so assessment included roadway, bike lane and sidewalk illuminance measurements. IESNA guidelines for field measurements were followed, with conditions and exceptions noted. Economic performance was evaluated using a simple payback and NPV methods for both retrofit and new construction values.

Efficient street lighting is a part of the City of Sunnyvale’s Framework for Environmental Sustainability. City policy mandates the use of efficient street lighting.

Lighting Assessment

Consistent with the demand of safety of the city, the ANSI/IESNA RP-8-00 roadway lighting standard was chosen as a primary method of assessing lighting quality. The standard specifies lighting metrics covering a variety of different roadway types and carefully defines a measurement methodology to validate conformance. Because there are so many roadway configurations, each of which has a particular lighting requirement. As a representative roadway configuration, the city chose a particular stretch of Fremont Avenue, a 4 - 6 lane roadway with a median island and center-mounted twin-armed streetlight poles. The evaluation covered only this roadway scenario with specific lighting products provided by the vendors.

The ANSI/IESNA RP-8-00 standard allows the choice of three different evaluation methods for determining standard conformance. Although computer modeling was used for all three methods, the illuminance method was chosen for the field evaluation due to instrument availability and simplicity of the measurement process.

Other aspects of lighting quality were also addressed as a part of the study. Correlated color temperature was measured. Controlled digital photography was employed to evaluate color rendering differences between the lights.

Outdoor Street Lighting SolutionsEstablishing The Measurement Grid

There were challenges in establishing a measurement grid in the test area. The result was that not all luminaires were exactly aligned along the median but were generally within two feet of a line along the center of the median. The varying roadway width was dealt with by assuming a uniform lane width, conforming to the narrowest section of Fremont Avenue. A uniform measurement grid was laid out accordingly to allow a fair comparison of the three sections of the test area - the major difference being the narrower pole spacing for Vendor C (137’ versus 143’). The varying roadway width combined with a uniform measurement grid meant some of the sidewalk measurement points were actually laid out on the roadway.

Monitoring Plan

The Monitoring Plan consisted primarily of illuminance measurements and time series electrical power measurements. These included:

Horizontal and Vertical Photopic Illuminance

Correlated Color Temperature

Voltage, Current, True RMS Power (Watts), RMS Volt-Amps, and Power Factor

Luminaire temperature

Controlled digital photographs of objects to illustrate qualitative performance

Horizontal Illuminance

Luminaires were mounted approximately 31feet 6 inches above the roadway on 8-foot mounting arms extending from poles in the roadway median Horizontal illuminance levels were taken with a Minolta T1 Illuminance meter. The meter had a photopic detector mounted on a tripod at a height of 18 inches above ground. It was operated remotely using a 6 foot 6 inches trigger cord.

There was no light source behind the operator. The operator, dressed in dark clothing, tookreadings from a crouched position six feet away from the light meter to minimize any effects on the readings. The meter has a precision of 0.01 foot-candles. The meter was leveled before taking each measurement using the tripod bubble levels. Although the ANSI /IESNA RP-8-00 standard specifies measurements 6 inches above the pavement, due to equipment limitations, we measured at 18 inches. However, modeling shows that measurements at 18 inches should introduce no more than a 1% error in LED average illuminance for purposes of establishing standards conformance.

Vertical Illuminance at Sidewalk

Vertical illuminance levels at the sidewalk were taken with a Minolta Chroma Meter CL200 mounted on a tripod at a height of 4 feet-6 inches as per ANSI /IESNA RP-8-00 standard.

Correlated Color Temperature

Correlated Color Temperature (CCT) values were recorded at each luminaire using the Minolta Chroma Meter CL200. The meter was unable to calculate CCT for the high pressure sodium luminaires due to meter limitations in measuring CCT in the range 2000K and below. Instead, for HPS luminaires, X, Y, Z tristimulus values were recorded and later converted to CCT. CCT was measured at three different positions for each luminaire and averaged to obtain the result.

ANSI/IESNA RP-8-00 Standard Metrics

The ANSI/IESNA RP-8-00 standard lists a variety of metrics required - organized around three different methods, any one of which can be used to demonstrate conformance. ANSI/IESNA RP-8-00 also lists metrics for sidewalk illuminance.

The ANSI/IESNA RP-8-00 column in the table lists the standard requirement. As can be seen, Vendors A and B are standard conformant. Vendor D (HPS) in all metrics with average illuminance are far larger than required for standards conformance. Vendor C underperforms in several of the metrics for the test scenario.

Note: In the tables below, results that meet ANSI/IESNA RP-8-00 standards are green; those that fail to meet red.  mean bigger values are better and  means smaller values are better. Typically bigger illuminance values are better, while smaller ratios are better, smaller numbers indicate better uniformity.

Location on Roadway Middl West East Midd

Results (model) Unit RP-8-00 A B C D

Pole Spacing Ft NA 143 143 137 143

Horizontal Illuminance Average Fc >0.4 0.85 0.88 0.65 2.35

Horizontal Illuminance Average/Min <6 2.59 2.21 23.02 2.20

Roadway Luminance, Average cd/m2 >0.3 0.57 0.57 0.29 2.25

Roadway Luminance, Average/Min <6.0 2.11 2.32 7.91 2.63

Roadway Luminance, Max/Min <10.0 4.15 4.81 19.79 4.71

Veiling Luminance Ratio, VL max/L avg. <0.4 0.26 0.28 0.15 0.28

Weighting Average Visibility Level >1.6 2.81 2.83 3.59 3.30

Key: a > means bigger is better, > x means value must exceed x to be ANSI/IESNA RP-8-00 conformant

Modeled results are initial lumens, RP-8-00 standard mandates maintained lumens (see section on Light Loss)

Pedestrian Safety

Pedestrian safety is an important aspect for roadway street lighting for the City. Sidewalk illumination was therefore evaluated. ANSI/IESNA RP-8-00 specifies standard metrics for the sidewalk, including horizontal and vertical illuminance.

Results Unit RP-8-00 A B C D

Sidewalk Horiz. Illuminance Average fc >0.3 0.39 0.40 0.32 0.73

Sidewalk Horiz. Illuminance Average/min <6.0 2.17 1.82 3.56 1.62

Sidewalk Vertical Illuminance, min fc >0.08 0.25 0.39 0.11 0.75

Outdoor Street Lighting Solutions

 3D Rendering  

Outdoor Street Lighting Solutions

False Color Rendering

Outdoor Street Lighting Solutions

 3D Rendering  

Outdoor Street Lighting Solutions

False Color Rendering