Comparison of CFL-based and LED-based solar lanterns

Comparison of CFL-based andLED-based solar lanterns

A.K. MukerjeeCentre for Energy Studies, Indian Institute of Technology Delhi, New Delhi-110 016, India

E-mail: [email protected]

Solar lanterns are designed to replace hurricane lanterns for use in remote places where conven-tional electricity is not available. They not only provide illumination at night but are also instru-mental in avoiding the emission of greenhouse gases normally emitted from burning the wick andkerosene in the latter. Light is produced in a solar lantern by igniting either a compact fluorescentlamp (CFL) or a light emitting diode (LED) while the energy to do so is generated by a string ofsolar cells, called a solar panel, exposed to sunlight. This energy, generated during sunlight hours,is stored in a battery to be used at night. LEDs are the latest development as a source of light.Therefore the cost and performance of two solar lanterns, one based on a CFL and the other basedon an LED, have been studied and compared to determine the better device for low-level lightingin the future. The comparison is based on lumens/watt (lm/W) output of the device. It has beenfound that the LED- and the CFL-based system cost almost the same if they are used to replacethe hurricane lantern which has a light output of 40 to 50 lm. The life of the former is more,typically 10,000 to 50,000 hours with luminous efficacy of 47 lm/W, and its driving and controlcircuit is less complicated than that of the latter. The luminous efficacy of the latter is slightlyhigher, 50 to 60 lm/W, and it has a life span of up to 15,000 hours. On the other hand, LEDs areavailable from powers ranging from a few mW to 3 W, enabling lower-illumination lanterns to beconstructed as an almost exact replacement of the hurricane lantern. However, at higher levels ofillumination the CFL is still a cheaper source. The electrical efficiency of the circuit used with theCFL is about 82 % whereas that used with the LED is 69 % since it is based on an analog constantcurrent generator. The efficiency of the latter can be improved by using a switch-mode constantcurrent generator.

1. IntroductionSolar lanterns were made as a viable alternative to thehurricane lantern for use in the remote areas of Indiawhere conventional electric power was not available[Bhargava and Sastry, 1982]. Subsequently a model wasdesigned and fabricated [Mukerjee, 2000] to be marketedas desired in a project financed by the Ministry of Non-Conventional Energy Sources (MNES) (now renamedMinistry of New and Renewable Energy, MNRE), Gov-ernment of India, in 1992 with the objective of supplyingthe basic lighting needs of people living in those areaswhere they were dependent on the hurricane lantern forillumination [Dutta et al., 1993]. Since sunlight is freelyand abundantly available at all places not covered byclouds, it can be easily converted into electricity by solarcells, a string of which makes a solar panel. Details aboutsolar panels are given in the catalogue of Central Elec-tronics Limited (CEL) [CEL, 2007] and other manufac-turers. This electricity can then be stored in suitablebatteries, normally lead-acid maintenance-free type, to beused at night or in dark places. To produce light the op-tions were limited to either a general lighting service(GLS) incandescent filament lamp, the ordinary householdelectric bulb, or the compact fluorescent lamp (CFL),

since other devices such as the 1.2-m fluorescent tube areeither too bulky or consume too much power or both. Theobjective was simply to produce enough light to equal orslightly exceed that of the kerosene lantern – hence thename solar lantern. Since the cost of a solar panel is about(US)$ 4 per peak watt (Wp), the light output of the lampper unit power input, defined as its efficacy, had to be ashigh as possible to keep the cost of the solar lantern withinthe reach of the buyer. The clear choice was therefore theCFL with an efficacy of 50 to 60 lumens/watt (lm/W) [Os-ram, 2007] over the GLS lamp with its efficacy of about10-14 lm/W [Cayless and Marsden, 1983, p. 475].

CFLs are gas discharge tubes and therefore require highvoltages, of the order of hundreds of volts, to start glow-ing. For this reason an oscillator circuit with high outputvoltage and the required power to operate the tube has tobe constructed. This also must have a high electrical ef-ficiency, exceeding 80 %, so that most of the solar elec-tricity actually reaches the tube instead of being wastedin the circuit. The block diagram of the solar lantern isshown in Figure 1. A solar panel generates the electricity,which is given to the oscillator and the control circuit.The control circuit, in addition to operating the oscillator,also contains a charge controller which saves the battery

Energy for Sustainable Development • Volume XI No. 3 • September 2007

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from being damaged by preventing it from getting eitherover-charged or over-discharged. The ballast, in this casea capacitor, ensures that excessive current does not flowthrough the lamp and thus prolongs the lamp’s life.

The CFL is a miniature version of the normal 1.2 m(fluorescent) tube light. The 1.2 m lamp is a low-pressuregas discharge tube with two filaments at the ends. Thefinished lamp is filled with an inert gas such as argon, toa pressure of 200-660 Pa (1.5 to 5 mm of mercury). Atiny droplet of mercury is introduced which is used in thedischarge to create light. The discharge produces, in ad-dition to visible light, ultraviolet radiation which is thenconverted to visible light by a coating of phosphor on theinside of the tube [Cayless and Marsden, 1983, p. 185]. Thisconversion of wavelength is responsible for the increasedemission of visible light resulting in a higher efficacy.

Light emitting diodes (LEDs) have now come up as anenergy-efficient alternative to the CFL at low-level illu-mination, with a considerably longer life. Being solid statedevices, they can be operated with direct current at lowvoltage levels of 2 to 4 V. Hence it was an interestingexercise to compare lanterns made with these two lightsources.

The efficacy of LEDs has steadily increased over thelast few years. An interesting comparison among effica-cies of different light sources, and the progress the LEDshave made with time, can be seen in [Craford et al., 2001].It shows a steep rise in the efficacy of LEDs from 1985to 2000. The white light LED was in its infancy with anefficacy of 20 lm/W in 2000. Now it is 47 lm/W [Cree,2007] and is a strong rival of the CFL.

The basic LED consists of a junction between two dif-ferent semiconductor materials, one n-type and the otherp-type (illustrated in Figure 2), in which an applied volt-age produces a current flow, which generates light whencharge carriers injected across the junction recombine.

This p-n junction in the form of an integrated circuitchip is placed in a concave reflector with two wires at-tached to carry current to it, with an epoxy-based lens infront [Spring et al., 2003]. The reflector sends the back-ward-going light to the front whereas the lens focuses itat the desired angle, which can range from 15º to 100º.The frequency, and perceived colour, of emitted photonsis characteristic of the semiconductor material, and con-sequently, different colours are achieved by makingchanges in the semiconductor composition of the chip.

Figure 1. Block diagram of a solar lantern

Figure 2. A p-n junction (left) as a light emitting diode (right)


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[Mills, 2007] gives figures to indicate that there is a largevariation in the efficacies of the LEDs available in themarket. Therefore, care should be taken to select suitableproducts while fabricating lanterns.

Dependence on fossil fuels like kerosene and the re-sulting polluting greenhouse gases had also to be reducedfor which the solar lantern was the obvious answer. Be-sides, the cost of transporting the kerosene to such loca-tions is high and the buyers, especially in hilly regions,have to travel long distances over difficult terrain to fetchit. Fuel-based lighting was shown to be significantly cost-lier than solar-powered CFL and LED alternatives, perunit of lighting service delivered. It was calculated [Joneset al., 2005] that the running cost of a hurricane-stylekerosene lamp is approximately $ 0.40 per 1000 lumen

hours (klmh), while that of a solar-CFL lantern is$ 0.17/klmh, and a solar-LED device costs $ 0.15/klmh.Furthermore, as LED efficiencies continue to improve,solar-LED products will become even more economical.[Dutt, 1994] gives the data about the output of differentsources as shown in Tables 1 and 2. The two tables showdifference in the light output from the kerosene wick sincethe material, the thickness and the burning conditions maynot have been the same in the two cases. However, anidea of the light outputs can be had by comparing thetwo. [Rajvanshi, 2005; 2006] gives additional data on theoutput from different sources, but the data of interest, thelight output from kerosene lanterns, does not differ muchfrom that given in Table 2. The 1 W white LED fromCree Inc., type XR7090WT, gives an output of 47 lm/W

Table 2. Another comparison of electric and non-electric light sources

Light source Flux (lm) Luminous efficacy(lm/W)

Specific fuel consumption(kg/klmh)

Fuel consumptionrate (kg/h)

Kerosene

Chirag (diya)[1] 21 0.26[2] 0.299[3] 0.006

Hurricane lantern 69 0.38 0.203 0.014

Petromax (mantle) 1303 1.25 0.056 0.073

Electricity

25 W incandescent 225 9 0.029[4] 0.007

60 W incandescent 660 11 0.023 0.016

Source: Selected from [Rajvanshi, 1987] as quoted in [Sinha and Kandpal, 1991].

Notes

1. The chirag or diya is a simple lamp made using a wick and a glass bottle.

2. Same as Note 2 of Table 1



Table 1. Some characteristics of different light sources

Light source Flux (lm) Colour[1] Luminousefficacy(lm/W)

Specific fuelconsumption

(kg/klmh)

Fuelconsumption

rate (kg/h)

Candle 12 Excellent 0.2[2] 0.5[3] 0.006

Kerosene wick 40 Excellent 0.1 0.8 0.032

Kerosene mantle 400 Poor 0.8 0.1 0.040

60 W incand. 730 Excellent 12 0.21[4] 0.016

16 W compact fluorescent 900 Good 56 0.005 0.004

1.2 W LED[5] 56.4 Good 47 - -

Source: [van der Plas, 1988]; original includes additional non-electric sources – carbide lamp, butane lamp, and gasoline mantle lamp; compact fluorescent data calculated here from datapresented earlier in the chapter.

Notes

1. Colour rendering index (CRI) is difficult to measure for non-electric sources, according to van der Plas [1988]. Thus, colour quality is shown here on a qualitative scale.

2. For non-electric lamps, the power input in W has been calculated using the higher heating value of the fuel.

3. Specific fuel consumption is expressed as kg of fuel use per 1000 lm-h of light (kg/klm-h).

4. For electric sources, we assume a conversion efficiency of 0.30 from kerosene to electricity, and express specific fuel consumption and fuel consumption rate as equivalent amountsof kerosene.

5. The LED data has been taken from [Cree, 2007].


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[Cree, 2007] and can be ranked as the second best sourceof light next to the 16 W CFL. This device costs $ 3 perunit in strip package and $ 3.50 if reflow-mounted on a1.9 cm round or star printed circuit board. It also has abuilt-in lens that can diverge light at an angle of 100º.

Two lanterns were, therefore, constructed for compari-son. One was made from white LEDs and the other wasmade from a 5 W CFL with a soft/cold start, the mostefficient firing mechanism, to give the maximum electri-cal circuit efficiency [Mukerjee and Dasgupta, 2007].

2. ExperimentsComparisons were made between the two circuits for theirelectrical efficiency and cost. Both these circuits were de-signed and fabricated by the author; one for the MNES,as mentioned earlier, but subsequently modified to com-pensate for the changes in the battery voltage with tem-perature, and the other to operate a white LED from aconstant current source. The first circuit, for the CFL, hasbeen widely manufactured and sold all over India and isvery reliable. The basis for this comparison is to find themost cost-effective solution for the replacement of thehurricane lantern, which should provide light for aboutthree hours with the required protections for the battery[TEC, 1993].2.1. The CFL-based circuitThe circuit of the whole lantern is split into two parts:(1) the charge-discharge controller as shown in Figure 3and the (2) oscillator plus the lamp as shown in Figure4. These are discussed below.2.1.1. The charge-discharge controllerFigure 3 shows the circuit of the charge-discharge con-troller of the CFL-based lantern, which can operate eithera 4-pin 5 W, or a 7 W CFL of any standard make. Thiscircuit is needed to prevent the battery, of the sealed main-tenance-free lead-acid type [Linden, 1995], from beingover-charged or over-discharged, thus prolonging its life.This also controls the switching of the oscillator, whichin turn drives the CFL, as shown in Figure 4. The de-scription of the oscillator follows later.

An LM 324 14-pin quad operational amplifier (fouropamps in one envelope) is used to operate the controller.The four sections of the opamp are indicated by four tri-angles with their accompanying components. One section,U3C, with its associated components, makes a stable 5 Vregulator used as a reference source. U1A uses this volt-age to form a 14.5 V feedback regulator with the P-chan-nel MOSFET MTP 2955E as the series pass element.Diodes D1, D2, and D3 are low-voltage drop Schottkydiodes, which protect the circuit against accidental rever-sal of photovoltaic panel and battery polarities. DiodesD7 to D14 are 1N 4148 silicon diodes in the feedbackloop of the regulator, used to provide temperature com-pensation for the battery during the process of charging.The 12 V lead-acid maintenance-free battery is connectedbetween the B+ and B- terminals to store the charge gen-erated by the PV panel during daytime while the PV panelis connected between the PV+ and PV- terminals. U2Bacts as a comparator by detecting the voltage across diode

D3. When the battery is being charged the terminal 5 ofU2B is more positive than the terminal 6 and the greenlight emitting diode, D11, glows to indicate it.

When the battery voltage goes lower than 11.5 V theoutput voltage of operational amplifier U4D goes low andthe transistor Q1 stops conducting. This shuts down theCFL-driving oscillator, shown in Figure 4, while the redLED D14 gives an indication of “battery low”. When thebattery is charged from a partially discharged conditionthe series resistance of the PV panel reduces its outputvoltage to latch on to that of the battery plus some voltagedrop across the MOSFET and diodes that come in series.When the battery is fully charged the output of the regu-lator settles down to a fixed value of 14.5 V so that over-charging does not damage the battery. However, theregulator continues to furnish a small current to compen-sate the loss of charge, an inherent property of lead-acidcells, which is known as trickle charging. A double-pole,double-throw switch, SW 1, turns the lantern on/off manu-ally.

A 10 W solar panel is used to charge the 12 V battery.Although this is the nominal battery voltage its actualvalue really depends on its state of charge. This may varyfrom 10.8 V, for deep discharge, to 14.5 V for a fullycharged state for both lead-acid and valve-regulated lead-acid types [TEC, 1993; Linden, 1995; Berndt, 1993].Therefore, the open circuit voltage of the panel should be12/0.8 = 15 V so that it operates at its maximum powerpoint. Since there are some diodes and a MOSFET in thecharging path the panel voltage is usually kept between16 to 17 V to also account for the temperature rise in thetropics.2.1.2. The oscillator and the lamp circuitThe circuit diagram of the oscillator used to drive theCFL is shown in Figure 4. This is a current-fed, class-Dsinusoidal circuit in a push-pull configuration, describedin [Yarrow, 1959] and [Baxandall, 1959], that has a theo-retical efficiency of 100 %, which is the reason for itsselection. Diode D1 ensures that a negative polarity busvoltage from a solar panel or a battery does not damagethe circuit while the inductor L2 maintains a current-fedtopology. The value of L2 should be at least five timesthe primary inductance of the transformer T1 from its cen-tre tap. The primary voltage is then stepped up to about125 Vrms (root mean square voltage value) to ignite theCFL, which is either a 5 W or a 7 W device, through aballast capacitor C2. To help start the discharge in thetube, a shield, a thin strip of copper, is placed betweenthe two bent columns of the CFL and tied to its horizontalupper part with a few turns of thin copper wire. This ef-fectively reduces the length of the tube for creating a glow.

A Hewlett-Packard digitizing oscilloscope model54501A was used to measure the voltage across the lampat F3 and ground and the signal at point 4 of the secon-dary of the transformer, that is across R2, which was pro-portional to the current through the lamp. A built-inmultiplier gave the product of these two quantities to dis-play the power waveform. And since it is point-to-pointmultiplication, the power factor was automatically


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Figure 3. Charge-discharge controller of the CFL-based solar lantern


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taken into account. The power was then averaged over 16cycles to get a stable power value. A 3n3F capacitor, C3,is placed between the two filaments of the tube so that itprovides a current path through them when the inverteris switched on. Although this current of approximately200 mA is adequate for pre-heating the filaments, it alsoreduces the voltage across the tube because of the capaci-

tive divider formed by C2 and C3. Initially this low volt-age fails to start a discharge but when the hot filamentsemit enough electrons the voltage is sufficient to cause aglow. The slow heating of the filaments thus delays theignition and allows for a gradual increase in the intensityof the emitted light, which is called a “soft start”. Oncethe tube attains full conduction the voltage across it comes

Figure 4. Circuit diagram of the current-fed oscillator


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down to its sustaining value, which is about 30 Vrms fora 5 W CFL, and therefore the current through C3 at thislower voltage reduces.

Another factor that affects the current flow through thefilaments is the reduction of the oscillator frequency whenthe CFL lights up. The ballast capacitor C2, in series withthe tube effective resistance of about 170 ohms (Ω), comesin parallel with the secondary winding of the transformer.The shift in frequency is quite drastic as can be seen fromTable 3. The two effects combined reduce the currentthrough the capacitor C3 since its reactance increases atlow frequency while the voltage across it drops to 30 Vfrom the initial value of 125 Vrms.

For cold-starting of the CFL capacitor C3 is removedfrom the circuit. The circuit was cold-started and switchedoff 5000 times without any appreciable blackening of theCFL near its filaments, which was earlier observed for alimited number of cold start operations [Cayless andMarsden, 1983, p. 186]. The oscillator is started when thewinding of the base terminal of the transistors 2N6292 israised to 11 V by Q1 of Figure 3, the output transistor ofthe controller. When the battery voltage falls below a cer-tain value, corresponding to a level of discharge, the volt-age at the emitter of Q1 goes to zero, thereby shuttingdown the oscillator.

All resistor values are in Ω and 250 mW, 5% toleranceunless stated. All capacitor values are in microfarad (µF)unless stated.2.2. The LED-based circuitFigure 5 shows the circuit diagram of the 12 V LED-based solar lantern complete with the charge-dischargecontroller. The circuit is similar to that given in Figure 3except that a constant current source comprising transis-tors Q1 and Q2 has been added. Resistor R 31 has to beadjusted to give a current of 350 mA through the LEDsD17 to D19, which are placed in series. This circuit hasa poor efficiency, as shown in Table 4, compared to theone with the CFL. This is because of the power dissipatedin the transistors and the resistance R31.

3. ResultsThe solar lantern with a 5 W CFL gives a total light out-put of about 250 lm whereas the one with the LEDs gives150 lm. The light output data are the nominal values sup-plied by the manufacturers in their data sheets. This isbecause the lowest-power CFL available is 5 W, whichyields 250 lm, whereas the circuit of Figure 3 can sup-port only 3 white LEDs of 1 W each, which togetheremit 150 lm.

The overall electrical efficiency of the CFL-based lan-tern exceeds 80 % with a 12 V DC input. The correspond-ing figure for the LED-based lantern is 69.2 % because

0.445 (1.78 × 0.25) W of power is wasted in the constantcurrent generator. This wastage increases to (4.2 × 0.327)= 1.373 W, thereby reducing the efficiency to 63.7 %. Aswitch-mode design will yield a better efficiency figure.The suggested part is LM 3402/LM 3402HV by NationalSemiconductor [NS, 2006].

4. ConclusionA replacement for a hurricane lantern needs a light sourcethat can give an output of 40 to 69 lm, as given in Tables1 and 2. 5 W CFLs, used earlier since lower-power tubeswere not available, gave a lot more light than required.However, with the arrival of high-intensity LEDs in themarket only one or two are needed to give the requiredlight. With one LED in circuit the battery and the solarpanel size will also reduce and the whole system will costbetween $ 20 and $ 25.

The circuit given in Figure 5 has three LEDs and costsas much as that given in Figures 3 and 4 because the costof the oscillator is eliminated. This also requires a solarpanel of 8 W as against the 10 W panel used for the CFL-based lantern, which amounts to a reduction of 20 % inthe panel cost. However, the life of a white LED is verysensitive to temperature [Narendran and Gu, 2005].Thus, the following conclusions are drawn.1. For a direct replacement of the hurricane lantern, with

a light output of 47 lm, a single LED-based lantern ischeaper than a CFL-based lantern. The cost of this

Table 3. Key performance parameters shownfor soft- and cold-start CFLs

Type of circuit 4-pin(5 W)

soft start

4-pin(5 W)

cold start

DC input voltage (V) 12.06 12.06

DC input current (mA) 474 470

Output voltage (Vrms) on load 29.66 29.66

Output voltage (Vrms) without load 212 212

Output current (Irms) (mA) 156 150

Power output (W) 4.58 4.59

Efficiency (%) 80.12 80.96

Frequency (kHz) on load 25.8 26.5

Frequency (kHz) without load 41.0 80.6

Short circuit current DC (mA) on load 82.0 83.0

Short circuit current DC (mA) without load 34.0 34.0

Power factor 0.995 0.995

Table 4. Parameters when the LEDs are operated from the circuit of Figure 5

Input DCvoltage (V)

Input DC(A)

DC voltage across lamp (V)

DC through lamp(A)

DC voltage acrosslamp & Q1 (V)

Voltage dropacross R31 & Q1

Efficiency(%)

15.1 0.34 10.0 0.327 14.2 4.2 63.7

12.2 0.288 9.72 0.25 11.5 1.78 69.2


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Figure 5. Circuit diagram of charge-discharge controller for LED-based lantern


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whole system will be between $ 20 and $ 25.2. For higher illumination, a lantern based on a 5 W CFL,

because it is the minimum power available, is cheaper.For solar-powered street lights that should give higherlight output, CFL-based designs are still cheaper thantheir LED counterparts.

References

Baxandall, P.J., 1959. “Transistor sine wave LC oscillators, some general considerationsand new developments”, IEE, Vol. 106, p. 748.

Berndt, D., 1993. Maintenance-free Batteries, Research Studies Press, Taunton, Somerset,England, pp. 165-204.

Bhargava, B., and Sastry, E.V.R., 1992. “Solar lanterns: problems and prospects”, 6th In-ternational Photovoltaic Science and Engineering Conference (PVSEC-6), New Delhi, India,February 10-14, pp. 885-889.

Cayless, M.A., and Marsden, A.M., 1983. Lamps and Lighting, (3rd ed.), Edward ArnoldLtd., London.

CEL (Central Electronics Limited), 2007. Catalogue of Central Electronics Limited, 4, Indus-trial Area, Sahibabad 201010, Ghaziabad, UP, India,http://www.celindia.co.in/solar_photoVolt_module.asp

Craford, M.G., Holonyak, Jr., N., and Kish, Jr., F.A., 2001. “In pursuit of the ultimate lamp”,Scientific American, February, p. 62.

Cree, 2007. Data sheet of Cree XLamp 7090 LEDs, http://www.cree.com/xlamp.

Dutt, G.S., 1994. “Illumination and sustainable development, Part I: Technology and eco-nomics”, Energy for Sustainable Development, Vol. I, No. 1, May, p. 23.

Dutta, V., Saxena, A.K., Mukerjee, A.K., and Joshi, J.C., 1993. Performance Evaluation ofPhotovoltaic Based Lighting System, Centre for Energy Studies, Indian Institute of Technol-ogy, Delhi, May 20, report submitted to the Ministry of Non-Conventional Energy Sources,Government of India.

Jones, R., Du, J., Gentry, Z., Gur, I., and Mills, E., 2005. “Alternatives to fuel-based lightingin rural China”, paper presented at Right Light 6, the 6th International Conference on En-ergy-Efficient Lighting, Shanghai, 9-11 May.

Linden, D., (ed.), 1995. Handbook of Batteries, (2nd ed.), McGraw-Hill Inc., New York, pp.25.1-25.39.

Mills, E., 2007. The Lumina Project, Research Memo #1*, “Assessing the performance of5mm white LED light sources for developing-country applications”, Lawrence Berkeley Na-tional Laboratory, MS 90-4000, Berkeley, CA 94720, USA, May,http://light.lbl.gov/pubs/rm/Lumina-RM1.pdf.

Mukerjee, A.K., 2000. “Comparative study of solar lanterns”, Energy Conversion and Man-agement, Vol. 41, pp. 621-624.

Mukerjee, A.K., and Dasgupta, N., 2007. “Firing options for CFLs used in solar lanterns”,Proceedings of 3rd International Conference on Solar Radiation and Day Lighting (SOLARIS2007), February 7-9, New Delhi, India.

Narendran, N., and Gu, Y., 2005. “Life of LED-based white light sources”, IEEE/OSA Journalof Display Technology, Vol. 1, No. 1, September.

NS (National Semiconductor), 2006. Data sheet of LM 3402, October,http://www.national.com/JS/searchDocument.do?textfield=lm3402

Osram, 2007. OSRAM catalogue, http://www.osram.com/osram_com/Professionals/General_Lighting/Compact_Fluorescent_Lamps/CFL_Energy_Saver.html

Rajvanshi, A.K., 1987. Design and Development of Improved Lantern for Rural Areas, reportprepared for the Advisory Board on Energy, New Delhi.

Rajvanshi, A.K., 2005. Rocket Science for Rural Development,http://nariphaltan.virtualave.net/rocketscience.pdf

Rajvanshi, A.K., 2006. Development of Improved Lanterns for Rural Areas, Nimbkar Agri-cultural Research Institute (NARI), Phaltan-415523, Maharashtra, India, February,http://nariphaltan.virtualave.net/lantern.htm

Sinha, C.S., and Kandpal, T.C., 1991. “Optimal mix of technologies for rural India: the lightingsector”, International Journal of Energy Research, Vol. 15, pp. 653-665.

Spring, K.R., Fellers, T.J., and Davidson, M.W., 2003. Molecular Expressions MicroscopyPrimer Physics of Light and Color - Introduction to Light Emitting Diodes, October 9,www.micro.magnet.fsu.edu/primer/lightandcolor/ledsintro.html

TEC (Telecommunication Engineering Centre), 1993. “Solar photovoltaic power source forsingle channel VHF and similar systems”, Specification No. P520S93, Power Plant, Issue-II,Telecommunication Engineering Centre, Khurshid Lal Bhawan, Janpath, New Delhi-110001,India, September.

Van der Plas, R., 1988, Domestic Lighting, Working Paper WPS 68, Industry and EnergyDepartment, World Bank.

Yarrow, C.J., 1959. “Transistor converters for the generation of high-voltage low-current D.C.supplies”, IEE, Vol. 106, p. 1320.

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Comparison of CFL-based and LED-based solar lanterns