Friday , 14 August 2020

Reducing Carbon Footprint using Smart Fluorescent Street Lamps

Appropriate design for lamp module

One of the common problems of the existing caged fluorescent lamps is their maintenance. The lamps once installed on the pole are not attended to unless a complaint is received by the local body of its failure. As a consequence, the working lamps which are exposed to the dusty environment are generally observed to be dirty with a layer of dust accumulated on top of them. The caged structure prevents the cleaning of the tubes in the mounted position on the street poles. In this situation, the efficacy of the lamps is compromised with (up to 70% reduction in light output). Even if the cage of some designs can be opened, the exposed connections of the lamps make the cleaning of the tubes with a wet or damp cloth, risky and hazardous.

The lamp should, therefore, have a sealed construction and be modular with minimal connections (only the pair of AC supply wires) coming out to the external world. The sealed lamp unit should have IPX5 protection to counter the environmental problems. The sealed lamp unit should be easy to clean with a wet or damp cloth in a fitted condition inside a fixture.

Since the transparent material is exposed to UV light, it has a tendency to degrade after a sustained period if it is made of ordinary plastic or polycarbonate. A material such as glass or ‘lexan’ (a special resin that is resistant to UV light), should be used to ensure that it continues to pass through it over 90% of the light produced by the lamp even after years of operation.

Appropriate design for lamp fixture

The fixture should be retrofittable onto the existing mounting arrangements. The design should be simple and low cost. Its main purpose is to protect and house or shelter the lamp module. Additionally, it should direct the light and offer partial ‘Cut-Off’ so that maximum lumens are directed to the place of interest, namely the section of the road below it and surrounding area around it. The light reflecting surface should be accessible and easy to clean.

While undertaking the design of the lamp, the cost increase if any should be limited so that the same can be recovered within 18 to 20 months through the energy savings that accrue through its usage.

The Light SaberTM Lamp

After listing out the requirement specifications, the design of the new energy efficient lamp, which we call the Light-SaberTM was carried out. Depending on the width and category of the street, we decided to arrive at different models, and this resulted in the development of three different lamps as follows:

  1. Light-SaberT5TM with maximum Lumen output of 2350 lumens and average consumption of 18 Watts
  2. Light-SaberT8TM with maximum Lumen output of 3000 lumens and average consumption of 25 Watts
  3. Light-SaberTWINTM with maximum Lumen output of 6000 lumens and average consumption of 60 Watts

While the Light-SaberT5 is suitable for small residential roads up to 30 feet wide, the Light-SaberT8 suits slightly wider connecting roads that are up to 50 feet wide, and the Light-SaberTWIN is for main roads with a width of up to 60 or 100 feet when used in singular and paired (two numbers of twin fixtures per pole) configurations respectively. Figure 1(a) and (b) show the Light-SaberT8 lamp module and fixture respectively. Its design is patented. As can be observed from Figure 1(a), the tube and the ballast is housed inside a transparent tube made of Lexan SLX resin. This transparent tube has a sealed construction to prevent ingress of dust, rain and insects. It is also hard enough to resist the stones pelted by miscreants to protect the inner glass fluorescent tube.

The fixture design (figure 1 b) is simple and at the same time, elegant and aesthetically appealing. The open construction allows easy access for wet cleaning of the lamp module.

The Light-Saber lamp is microcontroller based and therefore, stored programme controlled. Latest flash technology allows reconfiguration of the lamp depending on seasonal requirements (since winter nights are longer than summer nights). The intelligent software is able to detect these seasonal change requirements and adjust its characteristic curves for best light utilisation in every season (Figure 2). These seasonal adjustments take place silently, smoothly and automatically with every season without any need for reconfiguration. Hence, there is no need for remote gadgets or for any additional external equipment.

These intelligent lamps also incorporate a patented mains switch based remote setting facility wherein, using the same common mains switch, the settings of all the lamps in the feeder can be conveniently changed from one characteristic to another if so required. The other salient features of the Light-Saber lamps are as follows:

* Three Intensity Control Patterns (a) Automatic (b) Winter, and (c) Non-Dim

* Automatic seasonal change setting requiring no manual intervention

* Memory ensuring the continuation of dimming cycle in case of momentary power failure

* Setting of new cycle as per the seasonal requirement automatically every night

* Low Ballast Losses – approx. 1½ Watt power dissipation

* Non-dissipative Dimming Feature for Additional Energy Savings.

* Programmed start / Warm start – hot ignition of the tube to enhance tube life (enabling the lamps to be switched on and off without reducing useful life by preheating the lamp electrodes)

* Controlled heating of lamp electrodes during dimming operation for enhanced tube life

* 50% longer tube life than with conventional ballasts (tube life = 15000 hours)

* Smart power: Constant light independent of mains voltage fluctuations

* Automatic stop: Facilitates the operating of the circuit within five seconds of lamp failure (safety stop), and the resetting of ballasts automatically after the replacing of the lamp

* Option of switching off the lamp when it cannot be ignited normally thereby preventing damage to the lamp and helping in saving energy

*Operating in the non-audible frequency range for a silent operation

* Limiting the short-circuit current and/or the current during the running-up of the lamp to protect the lamp electrodes from overloading, thereby enhancing the tube life

* Keeping the lamp current within specifications during mains voltage fluctuations

* Use of SMD (surface mount) components for better manufacturability and higher reliability

Intensity Control Curves

Figure 2 compares the light output of the Light-Saber Lamp with that of the magnetic ballast operated T12 lamps. The characteristic curves are plotted for two seasonal settings, namely,

1. Summer Night and

2. Winter Night

Power consumption and savings

Table 1 gives the Power savings with the Light-Saber T8 lamp when compared with Class C Magnetic Ballast operated T12 Lamp. The average consumption of the lamp over the year is approx. 27 Watts. This represents a 27 Watts savings on an average over the magnetic ballast operated lamp. If we consider the cost of energy to be र4/kWh, then this represents a savings of र421 per annum.

There are many power saving advantages of the Light Saber-T8 Lamps over Magnetic Ballast Operated T12 Lamps. Some of them are: Reduction in losses due to shift from magnetic ballasts to electronic ballasts of the lamps (savings of 8 Watts); reduction in losses due to shift in size of fluorescent lamps from T12 to T8 lamps (savings of 4 Watts); increase in efficacy (efficiency of lumen output) of the fluorescent tube due to high frequency (50kHz) operation instead of 50Hz operation (10% savings); increase in efficacy due to selection of more efficient (5 star rating) fluorescent tube that offers 3250 lumens instead of 2600 lumens (20% savings); savings due to Constant Power Consumption that is independent of line voltage variation (approx. 15 to 20% savings) and operation at Unity Power Factor – Reduction of line current to half, resulting in 75% reduction in Line losses (approx. savings of 4 Watts).

Dr Vithal Kamat
Centre for Apparent
Energy Research


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