Tshwane ~ Power Matla Innolumis
16223
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Tshwane

Pilot sites were identified in Centurion (Lyttleton) across the municipality office where traditional HPS streetlight fittings (ranging from 70W to 250W) were retrofitted with LED streetlight fittings. Qualitative and quantitative light and electrical power measurements were taken on all the sites, economic cost estimated, and qualitative survey to be gauged with the resident survey. Different types of LED streetlights (Photopic & Mesopic) were used in this pilot to analyse the performance on different design concepts. The LED streetlight lighting project was conducted as part of the energy saving program of the City of Tshwane Municipality.

 

Pilot Site Information and Light Measurements

For the purpose of this pilot, no changes were effected on the street conditions i.e. the streetlight pole height & pole spacing remained as was with HPS.

 

For light and energy measurements, instruments with valid calibration certificates were used throughout the pilot viz, Solar Light Meter SL3101 and Fluke Energy analyser 1730 respectively. The Photopic, Scotopic, and Visual efficacy light levels were measured as per unified system of photometry recommended by RENSSELAER’s Light Research Centre.

 

Light and power measurements on HPS fittings were taken on the 29th of May 2014 between 6:30PM and 8 PM and signed off by the municipality official prior to installation of LEDs. Retrofit LEDs were installed on the 9th of June 2014; light measurements were taken on 19 June 2014 between 6:30PM and 8PM – also signed off by the municipality official.

 

70W HPS Site: Centurion, Lyttleton on Basden St between pole 13 & 14 – Pole spacing @38m, Photometric height@10m, road width @ 8m (single sided arrangement).

 

Table 1 : A summary of the test measurements 70W site.

Type Photopic lux Scotopic lux Visual efficacy lux SP Ratio
E ave E min E ave E min E ave E min
70W HPS 6.88 2 3.63 1 3.81 1 NM
30W LED Photopic 8.75 3 12.75 4 11.94 4 NM

 

150W HPS Site: Centurion, Lyttleton on Basden St between pole 37 & 38 – Pole spacing @ 38m, Photometric height @ 10m, and road width @ 8m (single sided arrangement.

 

Table 2: Summary of Test measurement 150W site

Type Photopic lux Scotopic lux Visual efficacy lux SP Ratio
E ave E min E ave E min E ave E min
150W HPS 8.69 3 4.31 1 5.19 1 NM
70 LED Photopic 13.31 5 19.06 7 18.81 7 NM

 

250W HPS Site: Centurion, Lyttleton on Gerhard St between pole 15 & 16 – Pole spacing @ 34m, Photometric height @ 10m, road width @ 8m(single sided):

 

Lighting Performance Summary

The above measurement results depict an interesting picture in terms of HPS & LED performance in relation to Photopic and Scotopic conditions. The results show that the HPS maintains a fairly high Photopic lux level whilst the Scotopic & visual effective lux levels are lower, keeping in mind that as night-time falls our eye’ sensitivity curve shifts from Photopic (daytime mode -555nm) to Scotopic (night time mode -507nm), hence we still experience poor visibility when subjected to HPS lights despite their high Photopic lux levels because of the misalignment of its Spectral Power Distribution as depicted on figure 1.

 

On the other hand the Photopic LED maintains comparatively higher Photopic, Scotopic and Visual Efficacy lux levels, thus outperforming the HPS in terms of the unified system of photometry measurement.

 

The variable nature of these measurements goes to show that the Photopic measurements alone do not give a full picture in terms of the performance of light sources in outdoor or street lighting application. It is a given that our eyes remains the best measuring tool for visibility – however the advancement in light measuring equipment has added a lot of value when it comes to documenting the scientific aspect of lighting.

 

Electrical Demand and Energy Savings

Power analysis was conducted on single samples of each respective Streetlight type e.g a power analyser was connected on one 250W HPS, one 90W LED, etc. The meter was left on the streetlight pole to run overnight so as to allow sufficient data logging sessions. The raw data extracted from energy analyser was used to compile the energy summary table below.

 

Table 4: Energy consumption summary

Streetlight Type Power (Watts) Savings(watts) Savings%
Min Max
70W HPS 85.3
30W LED 40.55 44.75 52%
150W HPS 167.6
70W LED 84.5 83.1 50%
250W HPS 250
90W LED 90 160 64%
120W HPS 120 130 52%

 

 Customer Acceptance

NTL Lemnis and Tshireletso will, in conjunction with City of Tshwane Municipality conduct a customer acceptance survey during the course of the pilot to gauge the general public’s level of acceptance or feedback on the LED Lights as compared to the HPS Lights.

 

The questionnaire form will be filled by pedestrians and drivers, then compressed in a summary table below.

 

Table 5: preferences expressed for new or old lights

Preference Number of Respondents
Prefer new lights 15
Prefer old lights 1
No difference 3

 

Closing Summary

LED street lighting has proven to be a worthy investment for municipalities and commercial customers. Their higher performance vs HPS’ combined with growing acceptance.