Domestic Lighting for Off-Grid Homes

The use of electricity to provide lighting services usually has very high priority among homeowners living off the grid. This is because electric lamps have major advantages over their nonelectric counterparts (such as kerosene lighting and candles), including increased levels of light, better quality light, greater ease of use, and lower cost per unit of light output. However, there are few incentives to apply energy-efficient lighting in conventional rural electrification (grid extension).

Electricity tariffs are often low and do not provide strong incentives to choose the optimal lighting source. In addition, alternative more efficient lamps are either not available or consumers lack information about them. 

In contrast, when solar photovoltaics provide electricity for rural lighting, the high cost of electricity per unit motivates more careful selection of the lamp or are already included in the kit that comes with the purchase of a photovoltaic system. However, cheaper, less efficient types of electric lamps may be more appropriate under certain circumstances.

New types of low-wattage electric lamps have entered the market in the last decade. These new applications and the changing focus of rural development planners toward photovoltaics (or rechargeable batteries) as a source of electricity prompted the present update of the state of the art in household lamps.

Off-Grid Lighting Technologies

Quality light is a critical – and often unrecognized – tool in community development. There are an estimated 2 billion people in the world who rely on inferior lighting systems (i.e., kerosene wick lamps) and pay far more per unit of light than those in the developed world. 

Without light, rural development is inhibited as people spend their nights “in the dark” and are unable to engage in many types of evening activities that those in the developed world take for granted.

Today, high-quality lighting technologies are available at affordable prices for all types of lighting systems. Solar electricity is an ideal, cost-effective power source for many lighting energy requirements.

Lighting Considerations: What Type of Light do you Need?

There are several general categories of lighting – each requires different types of light and, often, different types of lamps (also called luminaires). Lighting needs can be divided into 3 general categories, broadly described by the amount of light provided:

Measuring Light Output

The total output from a light source is measured in “lumens”.

The brightness of light on a given surface is measured in lumens per square meter (or lux).

• “Ambient” lighting provides a minimum amount of illumination for people to see each other and move about,
• “General lighting” provides enough illumination for reading or viewing objects,
• “Task lighting” provides bright enough light for close work and viewing detail.

Table 1: Lighting Applications and Examples

Although the amount of light is important, there are a number of other factors that need to be considered when choosing lighting systems.

Duration: How long is the lighting required? This is crucial for energy calculations and the design of energy supply systems. For example, security lights left on all night use much more energy than household lights left on for a few hours.

Lighting fixtures and reflectors: The light fixture, which directs the light to the area needed, is often as important as the luminaire itself. With solar lanterns, the spread of the light is crucial to consumer acceptance. Most task lighting luminaires require some type of reflector to concentrate the light where it’s needed. A good reflector reduces energy consumption.

Cost: This will normally be the most important determinant in your choice of lighting system. The costs of various lighting options are considered in detail below.

Portability: Do the end-users require lights that are portable, or lights that are for a fixed place or room?

Spare parts/Standardization: The wide variety of bulbs and tubes often causes problems. Local spare part availability should always be considered when lamps are bought internationally for rural LDC “projects”.

Lifetime/Quality: The lifetime of bulbs, mantles and lighting electronics is important when considering alternatives. There may be a trade-off between lower-priced luminaires and higher priced ones.

Other lighting considerations (adjustability, light color, etc.): Some customers may require lamps that can be dimmed. Others may be particularly sensitive to light color. These needs should be factored into lighting choices.

2. Off-Grid Lighting Technologies Options

A wide range of options, at a wide range of prices, are available to meet lighting demands. Table 1 presents the most common options:

Table 2: Lighting Options for Off-Grid Rural Households and Institutions

Option 1: Fuel-Based Lamps (candles, kerosene, LPG, white gas, etc.)

Electric lamps are superior in most regards to fuel-based lamps. When grid electricity is available, candles, kerosene lamps and gas lamps are unacceptable for most lighting tasks, barring emergencies or aesthetic purposes. 

However, in off-grid situations, fuel-based lamps play a much more important role and have many advantages. They are already in wide use. They are portable. They have low incremental costs. Lanterns and fuels are widely available and are often locally made. Therefore, planners should not completely discard these technologies to replace them with electric lights.

Fuel-based lighting technologies use the flame from burning fuels to produce light. Light quality varies depending on the lamp technology. These lamps expose users to open flames and should not be used where there is a danger of fire. Some of them produce smoke or CO2, and should not be used in enclosed spaces.

Candles are the simplest and cheapest means to provide lighting in an isolated, non-grid situation. However, the light output of a candle is only suitable for ambient needs where the danger of fire is low. Candles are an unacceptable choice for general lighting.

Kerosene lamps are available in three general types:

• Wick lamps use wicks dipped in kerosene to produce a flame. Wick lamps are similar to candles in light output, but give off smoke and particulates.
• Hurricane lamps are like wick lamps but enclose the flame in a glass case, making the lamp portable and safer. Hurricane lamps give off much less smoke and have an adjustable flame.

Pressure lamps vaporize kerosene and burn it on a “mantle” instead of a wick. The glowing mantle gives off light that is much brighter than other kerosene lamps (in fact the mantle has an intense glare), but it is also noisy and maintenance intensive.

Gas lamps, like pressure lamps, burn gas fuels (LPG, biogas, etc.) on a mantle. Gas lamps should not be placed in unattended situations, as there is some danger of fire or explosion if flames are accidentally extinguished when the gas supply is left on.

Technology Availability: All types of kerosene lanterns are widely available throughout the developing world. LPG gas lamps are available in developing countries but less so than kerosene units. Biogas lamps are available in some countries; where unavailable they can be fashioned from conventional gas mantle lamps.

Fuel/Energy Availability: Kerosene is widely available in most parts of the world. In extremely remote areas, diesel is often substituted for kerosene. LPG gas is less accessible in many regions, and it is necessary to check each area before deciding on the technology.

Spare Parts and Service: Spare parts for fuel-based lamps are commonly available where each technology is available.

Optimum Situation: Fuel-based lighting technologies should be considered as a first choice only in situations where infrastructure for PV/RET systems is not available (i.e. no battery replacements) or where there is no capacity to meet the high first costs of PV/RET systems. All off-grid situations should keep a few kerosene or LPG lanterns on hand as back-ups and/or as portable lighting systems.

Option 2: DC Electric Lighting Systems

Electric lighting systems are superior to fuel-based lighting systems because of convenience, cost, safety, and overall quality of light output. Small, 12 or 24V DC lighting systems are appropriate for systems of between 1 and 20 lights. They can cost-effectively be powered by lead-acid or nicad batteries recharged by PV, wind, and, in some cases, generator sets or central recharging stations.

It is often economical to have a number of dispersed lighting systems rather than a central interconnected system. 

In general, DC lighting systems should use fluorescent-type light fixtures, as they are much more efficient than incandescent or halogen alternatives. Low-power incandescent lights (3-10 W) can be used for ambient lighting needs. Halogen lamps with reflectors are ideal task lights. Note that PV lighting systems must be properly sized, using the daily energy requirement. Wind turbines can also be used to power lighting systems.

Table 3: PV Lighting Kit Prices

PV Lighting Systems

• Solar Lanterns: Solar lanterns incorporate a solar module, a battery, and a light into a single unit. They can provide high quality portable or backup emergency lights in a number of situations and range in price from US$150 to $350.
• Component-based PV Lighting Systems. One advantage of PV-based lighting systems is that they can be built up on a modular basis over a period of time. Where financing is a constraint for project planners or consumers, they can buy systems in small pieces.

  For example, end-users can buy a 10 Wp module, a battery, a charge regulator, and one or two lights, and expand the system eventually to power many more lights and radio/TV appliances. When buying on a component basis, local manufacturers of lamps, charge regulators, and batteries can also be used, thereby building an infrastructure for the supply of spares. A 2 light starter system can be purchased in most parts of the world for under $250.

• Kit-based PV Lighting Systems. Kit or full-sized PV systems are best for consumers or projects that can purchase equipment up-front. They are available in 2-20 light systems or can be designed for even larger needs (i.e. 40 lights) by suppliers. Table 3 shows typical prices for a 4 light system.

Technology Availability: PV lighting systems and components are now widely available in developing countries and on international markets. See PV light suppliers.

Fuel/Energy Availability: PV lighting systems depend on proper sizing and readily available solar radiation. 4 kWh/m2/day is considered a minimum for economic performance in developing countries.

Spare Parts and Service: PV systems require a minimum level of technical maintenance abilities. They also require a good source of spare bulbs/tubes, and batteries (batteries normally last 2-5 years before replacement).

Optimum Situation: 12V PV lighting systems are best used in small off-grid institutions, commercial establishments, and households. DC lighting systems can also power with black and white TVs and radio/cassettes; however, when end-users desire larger appliances (videos, color TVs, projectors) as well, it often makes sense to step up to 240 AC systems. 

Because of their simplicity and safety, 12V systems are nearly always better when technical expertise is limited on site. Example rural system types might include: Lighting for 4 rooms in a rural office or house, lighting for 6 classrooms, a laboratory and staff offices in a school.

Option 3: 110/240 VAC Electric Lighting Systems

It may be economically viable in some situations (generally larger systems) to choose 240 or 110 VAC powered lighting systems. AC systems can transmit power long distances (unlike low voltage dc systems). For example, a hospital with 15-20 widely dispersed wards might find it easier to distribute 240 VAC power than to use low voltage DC. 

Secondly, AC power can run other standard appliances in addition to lights. 

Thirdly, AC power systems and lighting fixtures do not need to be changed if the site is eventually connected to grid power. Finally, AC power systems easily deliver more power than 12 or 24VDC systems.

• Stand-Alone Generator (without batteries). When there are a large number of lighting points (50+), stand-alone generators (petrol or diesel “gensets”) may be economically viable for a few hours each night, particularly when there are other loads that are required occasionally (pumping, X-ray, computers – see also Audio-visuals). If the genset must be run more than a few hours, these systems are invariably an expensive solution. Note that in this system, the generator must be started up even if a few lights are needed.
• Generator plus Battery Charger/Inverter. When a genset has excess capacity, it may be a good idea to use a generator to charge batteries through an inverter/battery charger, and then to use the stored power to run lighting loads (in this case fluorescent lights should be used). For example, the genset might be needed for a pump or workshop during the day; it could charge batteries, and the batteries could run lights at night.
• PV/Hybrid System plus Charger/Inverter. Gensets can be used as backups to PV or RET power systems. In such situations, the generator would only be run when there was not enough solar/wind power. The advantage of this type of system is that the costs and size of the generator would be reduced. The disadvantage of this type of system is the increased complexity and higher up-front costs. A supplier would be able to recommend whether this type of system is viable.

Technology Availability: Generators are widely available. Inverter/battery chargers are a fairly new technology but are considered reliable. They should be carefully chosen by experts.

Fuel/Energy Availability: Fuel availability will be a crucial requirement for situations that use generators.

Spare Parts and Service: The costs of running, servicing, and fuelling generators should not be under-estimated. As well, keep in mind that inverters, though reliable, can break; if the system relies on inverters and the inverter goes down, then the whole system goes down.

Optimum Situation: Optimum sites for AC electric systems are large institutions where there are more than 50 lighting points. As well, AC systems are best in places where there is already a requirement for genset to power 110/240VAC appliances or power tools.

Suitability of lights for different tasks

With information about the spatial distribution of luminous intensity, it is possible to make qualitative statements about the suitability of different light types for different tasks. For orientation lighting, very low illumination levels of 5 lux (lumens per square meter) or below are acceptable. 

General lighting requires 10 to 50 lux, and task lighting at least 50 lux (Table 1). Lights with a lumen output of less than about 20 are usually suitable only for orientation lighting. Although most users want one or more orientation lights inside or outside their homes, the typical solar home kits do not include them because of their low efficiency.

Table 1: Suitability of lights for different tasks

+++very suitable; ++ suitable; + possible; – less suitable; — unsuitable

Laboratory Tests of Lamps

From mid to late 1997, the Netherlands Energy Research Foundation (ECN) carried out a series of laboratory tests, focusing on measuring and comparing the light output characteristics and energy consumption of a number of different electric and nonelectric lamps. 

The results complement the lamp manufacturers’ data sheets. ECN also evaluated other, nontechnical aspects of value to consumers, such as color and ease of use. The electric lamps tested are in the low-power range and are already in use in solar photovoltaic systems or have the potential for such use (12 Volt, DC).

Three categories of lighting are relevant for solar photovoltaic systems or other direct current applications for households in developing countries: general lighting (illumination of a whole room), localized and task lighting (illumination of a part of a room such as a table), and orientation lighting (sufficient only to recognize shapes). 

Both the luminaire and the type of lamp determine overall lighting characteristics. Consumers can usually satisfy their lighting needs by buying an appropriate lamp with an appropriate luminaire.

The total output of visible light (luminous flux) is one of the most important characteristics of a lamp. Conversion of fuels or electricity into visible light takes place in a number of different processes and under different conditions, resulting in a wide range of luminous efficacy. Electric lights are far more efficient than non-electric lights. In the test, they consumed 65 times less power, on average, at the same output level of visible light.

The luminous flux of the lights in the test sample ranged from about 1 to 1,000 lumens for the electric lights and from 10 to 2,000 lumens for the nonelectric lamps. Power consumption ranged from less than 1 watts to 15 watts for the electric lights and from 60 watts (wax candle) to 1,400 watts for the nonelectric lights (petromax). 

For both types of lamps, the range in the levels of luminous efficacy was very wide: from 1.7 to 60 lumens per watt for electric lamps; and from about 0.1 to 1.4 lumens per watt for non-electric lamps. Different combinations of (electronic) ballasts and lamps (tubes) produced significant variations

Standards for light fixtures

There are neither international standards for solar photovoltaic systems nor their components. In formulating lighting standards, it is important to focus not just on the lumen output, but also on color, ease of use, availability, lifetime, tube blackening, and, in particular, cost, as these aspects are important to consumers. 

Lighting standards that may be adopted should:

• Set a minimum luminous efficacy, taking into account the effects of color
• Apply only to the luminous efficacy of general lighting (power consumption of about 4 watts or more), not to orientation lighting
• Include a maximum power level for orientation lights
• Have different luminous efficacy standards for lamps or luminaires with and without a reflector

Minimum quality norms can be proposed based on laboratory tests. The laboratory measurements of 36 lamps yielded a range of luminous efficacy of 25 to 47 lumens per watt. Fluorescent lights without a reflector averaged 37 lumens per watt. The empirical number of 37 lumens per watt should therefore be used as the standard for compact fluorescent (CFL) lamps without a reflector and for fluorescent tubes without any fixture. 

The tests showed that a fluorescent tube mounted on a fixture but without a reflector has a luminous flux about 5-10 percent lower than that of a tube without any fixture. The proposed standard for fluorescent tubes without a reflector is therefore 35 lumens per watt. ( “without a reflector” and “without any fixture” has me confused)

Assuming a typical value of 80 percent for the efficiency of a luminaire with a reflector, the proposed efficiency standard for luminaires with fluorescent tubes and a reflector is 30 lumens per watt. More detailed information about the test results will be available in a forthcoming ECN publication.

Options and Availability

For household applications in off grid or rural settings, there are numerous lighting options covering a wide range of lumen output levels, energy consumption, and costs. But many technically feasible alternatives for household lighting are not commercially available in developing countries. Consumers in rural areas, in particular, have very few choices of lamps. 

One reason is that lamp manufacturers do not appreciate the potential of the rural lamp market and believe it is too small for more efficient low-wattage lights. Field surveys have demonstrated, to the contrary, that a wider spectrum of lights, particularly in the low power range (1-10 watts), would better meet the cost and quality criteria of many rural customers. This applies to both photovoltaic installations and rechargeable (car) batteries.

In addition, consumers should be better informed about the different factors that should guide the purchase of a lamp. Better standards would improve consumers’ access to good information; printing the information on the lamp’s packaging would be better still. 

Above all, a larger range of lamps should be available in rural retail shops. Designs of solar home systems need to offer one or more low-cost, low-wattage lights for orientation lighting. When only orientation lighting is required, a low-efficiency, low-power (for example, 1 or 2 watts) incandescent light is better than a high-efficiency 6-watt light to meet both energy efficiency and consumer preferences.

Means of Lighting

There are a number of means to meet lighting demands. Candles remain the most widely-used lighting source in the world. Kerosene follows candles as the next most widely used energy source for lighting. There are a number of kerosene lamps, ranging from simple wick lamps (simple to “hurricane” with a glass globe) to high pressure kerosene (or “paraffin” as it is known in many parts of the world) lamps.  

Flashlights, powered by dry cell or rechargeable (general nickel-cadmium/nicad) batteries follow kerosene as the next most widely used source of off-grid lighting. These can range from simple hand-held flashlights used for simple tasks (walking, bike riding, etc.) to more complex fixed rechargeable lighting systems.  

Next in order of use are lights and lighting systems powered by lead-acid batteries (e.g., automobile batteries). These lights can be of the incandescent or the fluorescent type. People rarely use car batteries only for lighting. Lead-acid batteries tend to be used for lighting and other purposes, such as for powering radios, radio/cassettes, televisions and video (VCR) machines. 

Next in order of use are generating sets (“gensets”) either powered by diesel or petrol (gasoline, benzene). As with automobile batteries, gensets generally power far more than lights, and are generally not purchased only to provide lighting power. One of the most rapidly expanding sources of energy for lighting comes from photovoltaic (PV) systems. PV lighting systems, and the technology that goes with those systems, have reached virtually all parts of the globe.  

Lamps and Bulbs

Electrical lighting devices have changed dramatically over the past several decades. The original incandescent light (highly inefficient, short life span), is rapidly being replaced by more energy efficient, and healthier lighting. 

Fluorescent lights have been around for many years. They are readily available, much more efficient than incandescent lights, and are adaptable to virtually any form of electricity system. Newer, more efficient lights include halogen, CFLs and LEDs. 

This new generation of lamps is evolving very rapidly and is quickly being adapted from conventional grid-connected systems, for off-grid applications, including hand-held flashlights, PV lighting systems, and other isolated electricity systems. 

Helpful Terms and Definitions

candela: Unit of luminous intensity (cd)

CCT: Correlated Color Temperature = color appearance of the light source. Unit: Kelvin

CFL: Compact Fluorescent Lamp

CIE: International Commission on Illumination

cluster-LED: Recently-developed lighting technology based on output of Light Emitting Diodes. Cluster LEDs are more efficient and long-lasting than fluorescent lamps. They are best suited for task-lighting as their output is directional.

domestic: Usually refers to the household sector. Example: Families use domestic lighting for reading in the home.

fluorescent: light emitted from special inert gases (generally neon) when an electric current is passed through it. Fluorescent lamps are much more efficient than incandescent lamps, and are preferred over incandescent lamps for energy efficiency. However, it is not as efficient as halogen or LED.

general lighting: Illumination of a large area. Unit lux = lumen/m2

halogen lamps: lamps with very low wattage, that generate high intensity light through a combination of specially coated, highly efficient reflectors. Very low voltage with high efficiency delivery of light for low power.

illuminance: Luminous flux per unit area. Unit lux = lumen/m2

illuminous efficacy: Efficiency with which a surface is lit. Unit: lux/Watt

incandescent: an incandescent lamp produces light when its wire filament is heated by electricity to ‘incandescence. Wire filaments are made of tungsten.

lamp: Light source (such as incandescent bulb, fluorescent tube)

LED: Light Emitting Diode (a small, low-voltage light source)

light-emitting diode (LED): a type of diode which lights up when current is flowing through it. Commonly used as an indicator in charge controller

light color: the actual appearance of light emitted by lighting appliances.

lmh: Lumen-hour: luminous flux integrated over one hour

local lighting: Illumination of a (small) work area

localized lighting: Illumination of only part of an area

LOR: Light Output ratio = Luminaire efficiency

lumen: Unit of luminous flux (1m)

luminaire: Complete lighting system

luminous efficacy: Efficiency of lamp or luminaire. Unit: lumen/Watt

luminous intensity: Amount of light emitted in a certain direction

lux: Unit of illuminance

orientation light: Lighting which is just sufficient to recognize shapes

PLC: Type of CFL, with 2 or 4 tubes

pressure lamp: a term usually used to refer to a kerosene lamp that is charged to a high pressure (usually by hand) in order to achieve vaporization of the kerosene to aid combustion and generate a high-intensity light. The kerosene is burnt and light emitted through the ‘mantle’.

PV Lighting System: a system that includes at least a PV module, a battery, an inverter, and a light. Can include a large number of lights, preferably high-efficiency fluorescent, LED, halogen lamps.

RA: Color Rendering Index = Degree with which different colors can be recognized compared to a standard light source

reflector: Part of the luminaire with reflects light (usually downwards)

Summary

Lighting is one of the most important sources of energy demand in the world. Most people concerned with rural electrification and off-grid electrification, view lighting as a key to people’s demand for electricity. 

Recent studies show that this is not always the case, that people may want electricity first for television and radio/cassettes, but the lighting of homes, businesses, and institutions (schools, hospitals, clinics, government buildings) remains one of the most important demands for electrification. 

REFERENCES

Louineau, Jean-Paul, Mobido Dicko, Peter Fraenkel, Roy Barlow, and Varis Kodalers. 1994. “Rural Lighting: a Guide for Development Workers.” IT Publications in association with the Stockholm Environment Institute, London.

van der Plas, Robert, and A. B. de Graaff. 1988. “A Comparison of Lamps for Domestic Lighting in Developing Countries.” World Bank Energy Series No. 6. Washington, D.C.