Ekurhuleni ~ Power Matla Innolumis
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Pilot sites were identified in two towns i.e. Benoni and Boksburg 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 gauged with the resident survey. Different types of LED streetlights from different manufactures 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 Ekurhuleni Municipality, and the emerging technology program by Power Matla Innolumis’s former distributor NTL Lemnis Africa.


Photopic LED technology and scotopically enhanced (Mesopic LED) technology was used in this project.


For light measurements purposes, the latest lighting measurement technology was used to measure the Photopic, Scotopic, SP ratio and visual effective light levels.


Light and power measurements on HPS fittings were taken between 7:30PM and 12 midnight as a reference, and signed off by the municipality officials prior to installation of LEDs. Post installations, light measurements were taken on LEDs between 7:30PM and 12 midnight and also signed off by the municipality officials throughout the project.


Benoni – Lessing Street – Pole spacing @40m, Photometric height@10m, road width @ 6m (single sided):

To allow variety of measurements, a total of 9 LED fittings comprising of 3 x 36W Mesopic LED, 3 x 40W Photopic LED and 3 x 50W Photopic LED replaced 9 x 100W HPS fittings.


A summary of the test measurements are illustrated on table 1 and figure 1 below.

Type Photopic (lux) Scotopic (lux) Visual effectiveness SP Ratio
  E ave E min E ave E min E ave E min  
100W HPS 7.4 4.3 3 1 4.1 2 0.57
40W LED Photopic 5.3 2.6 7.5 3 8.3 2 2
36W ed Mesopic 2 1.3 5.8 3 4.4 2 3.8


Benoni – Cloudy Street – Pole spacing @ 40m, Photometric height@10m, and road width @ 6m (single sided):

A total of 10 x 56W Mesopic LED fittings replaced 10 x 150W HPS fittings.


Test measurement summary illustrated on table 2 and figure 2 below

Type Photopic (lux) Scotopic (lux) Visual effectiveness SP Ratio
  E ave E min E ave E min E ave E min  
150W HPS 7.4 3.6 4.1 1 4.6 2 0.57
56W LED Mesopic 3.1 1.1 8.8 2 6.9 2 3


Benoni – Fifth avenue – Pole spacing @ 40m, Photometric height@10m, road width @ 8m(single sided):

A total of 12 LED fittings comprising of 3 x 70W Photopic LED(Lemnis), 3 x 70W Photopic LED (Cerabix), 3 x 60W Photopic LED (Cerabix2), 3 x 60W Photopic LED (Cerabix)


Test measurements summary illustrated on table 3 and figure 3 below.

Type Photopic (lux) Scotopic (lux) Visual effectiveness SP Ratio
  E ave E min E ave E min E ave E min  
150W HPS 9.6 4.6 4.5 2 5.1 2 0.56
70W LED Photopic 10.2 4.2 15.2 6 13.1 5 1.8


Boksburg – Milkwood Street – Pole spacing @ 38m, Photometric height@7.4m, road width @ 7.6m (single sided):

8 LED fittings comprising of 4 x 24W Mesopic LED, 4 x 30W Photopic LED (Lemnis) replaced 8 x 70W HPS fittings


Test measurements summary illustrated on table 4 and figure 4 below.

Type Photopic (lux) Scotopic (lux) Visual effectiveness SP Ratio
  E ave E min E ave E min E ave E min  
70W HPS 5.7 1.7 2.9 1 3.8 1 0.59
24W Mesopic LED 3 2.1 9.2 5 7.3 3 3
30W Photopic LED 7.9 1.7 12.3 2 11 2 1.6


Boksburg – Trichardt Street – Pole spacing @ 45m, Photometric height@12m, road width @ 7.6m (staggered):

12 LED fittings comprising of 4 x 90W Mesopic LED, 4 x 110W Mesopic LED, 4 x 120W Photopic LED(Lemnis), replaced 12 x 250W HPS fittings.


Test measurements summary illustrated on table 5 and figure 5 below.

Type Photopic (lux) Scotopic (lux) Visual effectiveness SP Ratio
  E ave E min E ave E min E ave E min  
250W HPS 10 7 6.6 3 6.3 3 0.66
120W Photopic LED 15.4 8.2 23.4 11 21.1 10 1.56
80W Photopic LED(2) 11.7 7.5 19.5 11 16.9 10 1.66
110W Mesopic LED 6.5 3.2 18.4 8 14.4 6 2.96
90W Mesopic LED 4.5 3.2 12.8 9 10.2 7 3.1


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 fairly high Photopic lux levels 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.


On the other hand the Photopic LED maintains a comparatively higher Photopic and Scotopic lux level, and in most cases outperforming the HPS across the board.


Mesopic LED’s as expected shows a comparatively lower Photopic lux level (still meeting minimum requirements), good Scotopic/visual effective lux levels, the best SP ratio and uniformity ratio. And from a power consumption point of view, they also offer the best energy savings.


The variable nature of these measurements goes to show that 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 remain 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 measurements were taken by the municipality on each respective luminaire type i.e. HPS luminaires and LED luminaires to verify the rated wattages of the luminaires. As power monitoring was conducted by the municipality – they reported no significant variation in power consumption during the measured period. The hours of operation for both the HPS and the LED’s was monitored during summer (December 2013) so as to ensure same operational hours during power monitoring.


Replacement guide summary table for this pilot project

Current HPS fitting type LED Replacement type Energy Savings
100W HPS 36W LED Nicole Mesopic 64%
100W HPS 40W LED Nicole Photopic 60%
150W HPS 56W LED Nicole Mesopic 62%
150 HPS 70W LED Nicole Photopic 53%
250W HPS 90W LED Oprah Mesopic 64%
250W HPS 110W LED Oprah Mesopic 56%
250W HPS 120W LED Oprah Photopic 52%
400W HPS 170W LED Oprah Photopic 57%


Customer Acceptance

Some of the residents in the pilot sites neighborhood, passers-by pedestrians and drivers were engaged to obtain feedback on the new lights.


The first question asked of residents, pedestrians and drivers was if they noticed any change in street lighting. Out the overall 25 respondents, 22 felt that the new lights were preferable, while the other three had no particular preference or preferred the old lights.


Table 7: preferences expressed for new or old lights

Preference Number of Respondents
Prefer new lights 22
Prefer old lights 2
No difference 1

Economic Performance

Economic performance was evaluated primarily by simple payback of LED luminaires vs HPS luminaires. For calculation purposes, initial cost of LEDs, operating costs (energy costs), maintenance cost, and estimated lifespan were taken into account assuming current energy and LED costs.


Maintenance costs for the HPS included bulb replacements, ballast replacement, labour and cherry picker/vehicular costs for the each maintenance cycle. Maintenance costs were estimated for spot replacements in which lamps are replaced on an individual basis at failure, therefore assuming lamp or ballast replacement every 2 years. The fixture Replacement costs of the HPS fitting was not taken into account, assuming the fixture housing will have an extended lifespan, thereby making the maintenance estimates conservative.


The LED luminaires were assumed to have zero regular maintenance over the course of their lifetime due to their robust nature and long lifespan. Since maintenance costs for LED were effectively assumed to be zero, energy costs accounted for 100% of the annual cost.


Figure 6 illustrates Payback Periods in 5.5yrs on assumed current costs

Figure 7 illustrates KWh Consumption (savings)


Summary on Economic benefits

Some of the many benefits of retrofitting HPS to LEDs are as follows:

  • Immediate reduction in energy savings
  • Increased visibility with less energy consumption
  • No maintenance costs
  • Extended warranty
  • Contributing towards a greener environment (reduction in Greenhouse Gas Emissions).


LED street lighting has proven to be a worthy invest for municipalities and commercial customers. Their higher performance vs HPS combined with growing acceptance fast tracked the adoption of this technology.