TrafficInfraTech Magazine Linking People Places & Progress
With the Government of India focusing on issues like health, education of the masses, water supply, drainage and transportation through the municipalities and gram panchayats for urban and rural areas respectively, the issue of street lighting has not got its due attention. As a result, street lights have, over the years, gradually moved to dilapidated conditions while the street lighting system itself has become grossly ineffective. It is important to note that the subject of street-lighting does not merely deal with lighting for a street but more importantly, with lighting for people. Lighting offers a social identity, which is a key aspect of urban design. It directly affects the home environment of the masses and thereby, influences their lives. Hence, there is a need to push it up on the social and political agenda.
Cause for Deterioration in Street Lighting
In spite of the various community related benefits that street lighting offers, there are two main reasons for the steady deterioration of street lighting systems – both in urban as well as rural local bodies. They are accurate electricity billing and the use of CFLs
Accurate Electricity Billing:
Earlier, the energy meters installed on municipality/panchayat street lighting circuits either ran slow or often, didn’t function. The electric utilities often turned a blind eye to this issue. However, with strict instructions from the electric regulatory commissions, even the state run electric utilities are now made accountable. Owing to the now mandatory audit and accounting procedures and loss control, faulty meters have had to be replaced with highly accurate electric meters. All this has led to all local bodies accrue very high bills which many find difficult to clear. In this changed scenario, a reduction in the maintenance activity not only decreases the maintenance cost but also the number of working lamps. The local bodies find this to be an effective means to bring down the electricity bills to a manageable figure.
Use of CFLs: The widespread replacement of incandescent lamps by Compact Fluorescent Lamps (CFLs) in the western countries has had its impact in India as well. The constant bombardment of CFL advertisements by media has been so intense that they now also display the tag of ‘80% efficient’. This efficiency message has spilled over to the street lighting sector too and now four feet long fluorescent lamps (TL) and sodium vapour (SOX) and mercury vapour (MBF) lamps are being replaced by the less efficient and less reliable CFLs. The use of CFLs has not only resulted in lower efficiency levels but also lower illumination levels (ranging from 2 lux to 5 lux). It has increased the maintenance cost and the high intensity levels from a point source have also amplified the glare resulting in temporary blindness and accidents. In short, in the street lighting segment, CFLs serve well as indicator lamps (to help identify the location of the poles) but are highly ineffective in addressing the issue of street illumination – the main purpose of installing street lamps.
Coping with Greenhouse Issues in the West
As has been established above, the use of CFLs has been counter-productive and has added to the environmental problems inclusive of green house gases. The learning from the CFL episode is that before putting any product to use and bringing about a change, it is important to carefully and extensively test it from every angle. Some of the ways in which the western world is trying to cope with the greenhouse and efficiency issue are as follows:
P
hoto-electric cells: The western countries have been using photo-electric cells since a long time to control the street lighting system. These cells, which were earlier set to switch on at 70 lux and off at 35 lux, have been changed to now switch on at 35 lux and off at 17 lux respectively. This has resulted in a saving of about 2%.
Reducing the number of hours of operation: When the requirement of light is less, the lamps are switched off with the use of electronic time switches. However, both in urban and rural areas, this measure has gained little popularity.
Reduce the light output of the lamps (dimming them) as an acceptable alternative to switching off for a certain duration at night: Although the capital cost of dimming equipment is high the current and projected increases in energy costs are starting to make the installation of such equipment, even in the case of low wattage lamps used in residential areas, cost effective. The environmental benefits of reduced light pollution and reduced carbon footprint of the lighting system have made the dimmable lamp option the most acceptable practice. However, the use of centralised voltage control gadgets for dimming has been a failure due to inconsistent dimming among different types of lamps possessing different technologies (electronic vs. magnetic) on each feeder.
Design of an Efficient Street Lighting System for India
India being a tropical country with dusty roads, incessant rains, high temperatures and high power fluctuations, it is a challenge to design an efficient street lighting system. A sincere attempt has been made though at designing a lamp that accommodates the much sought after efficiency – ‘green’ features along with characteristics that counter the harsh environmental conditions. Mainly four aspects have to be kept in mind for this.
Appropriate lamp technology
Currently LED lamps are considered to be the latest technology innovations that can offer the longest life. Though the efficacy of LEDs is increasing every month, it is not able to match the efficacy levels of other more efficient technologies. Also, LED manufacturers have been unable to address its lumen maintenance problem – light output drops considerably after two years of use. Moreover, the exorbitant cost of the LED technology makes its use prohibitive today. While making a choice amongst the other lighting technologies and taking a decision on purchases, it has to be borne in mind that the LED technology will be ripe for street lighting at low cost in two to three years. Hence, the cost of the chosen lighting technology in the interim period should be recoverable within this period. This will facilitate its replacement with LED technology thereafter.
Amongst the balanced lighting technologies, though low pressure sodium vapour lamps are considered to be the best in terms of efficacy (>140 lumens per Watt), due to their poor colour rendering properties and non-availability in low wattages, and high cost, they are preferred to the other technologies only for lighting main arterial roads.
The technology that is low in cost and also comparable in terms of efficacy levels is the fluorescent technology. The fluorescent tubes come in a wide range of shapes and sizes, ranging from 5 Watt CFLs to 58 Watts TLs. Amongst all shapes and sizes, the straight four feet long TLs are the most efficient. India has been familiar with the four feet TL lamps for over five decades, and has been using them not only for street lighting, but also in domestic, industrial, and commercial sectors. Over the years, the TLs have become more and more efficient and the latest range of T8 and T5 tubes has efficiency levels that exceed 90 lumens / watt. The lumen output of the TL lamps should exceed 2500 lumens as distance between the poles will not have to be reduced then.
While making a choice amongst the other lighting technologies and taking a decision on purchases, it has to be borne in mind that the LED technology will be ripe for street lighting at low cost in two to three years. Hence, the cost of the chosen lighting technology in the interim period should be recoverable within this period. This will facilitate its replacement with LED technology thereafter.
Appropriate ballast technology
As per the European Standards Committee, the ballast that occupies the topmost position in the efficiency ladder is the Class A1 ballast. A timer based dimmable ballast occupies this category. Hence, our interest is to drive a TL lamp with a Class A1 ballast that consumes approx. 1 Watt. This is achievable by using a fast switching device (to reduce the switching losses), namely a MOSFET instead of a transistor. The drive to the MOSFET is achieved using a semiconductor lighting ASIC chip. The ballast should be a warm start ballast which ignites the lamp only after a couple of seconds of filament preheating so that the life of the lamp can be enhanced.
The ballast should operate at a power factor very close to unity (PF approx. 0.99) and the Total Harmonic Distortion (THD) should be less than 10%. This can be achieved by incorporating an active power factor correction circuit. The ballast should operate at a constant power and offer constant light output even when the voltage fluctuates.
