1.0 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 metre (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
Type of Lighting
Lighting Level Lumens/m2
Lights an area so that people can see one another and move about.
Provides enough light for detail rendering
5 - 50 lux
Localised or task lighting:
Provides enough light for close work and full illumination.
50 lux or more
Although 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 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. Good choice of reflectors reduces energy consumption.
Cost: This will normally be most important determinant in choice of lighting system. Cost of lighting options is 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/Standardisation: 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 colour, etc.) Some customers may require lamps that can be dimmed. Others may be particularly sensitive to light colour. 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
TYPES OF OFF-GRID LIGHTING
Acceptability for lighting tasks
Fuel-based Lighting Alternatives
Pressure lamp (mantle)
High fuel consumption.
LPG gas lamp
Electric Lighting Technologies
Torch with incandescent bulb
Directional light only.
Incandescent bulb (10W)
Low first cost. Widely available. Expensive use of PV power.
Expensive use of PV power.
12V Fluorescent tube
Some task lighting
Electricity (12V dc)
High first cost. Very efficient. Best matched to PV systems. Need to standardise bulb type.
240 VAC fluorescent tube
Extremely high reliability and lifetime.
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 for 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 the 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, light output of candles 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 vaporise 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 which also is 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 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
Typ. Market Price [US$]
PV module 50 Wp (4.5$/Wp)
Battery 100 Ah (lead-acid)
Cables, switches & mounting struct.
40 - 100
Fluorescent lamps 11 W x 4
Commissioning & overheads
System costs (not including taxes)
$ 580 - 950
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 back-up 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 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 establishment and households. DC lighting systems can also power with black and white TVs and radio/cassettes; however, when end-users desire larger appliances (videos, colour 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 which 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 back-ups 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 in 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.
For further reading, in addition to those you can access by clicking on the further reading icon below "Lighting" below, try:
"Rural Lighting Services: A Comparison of Lamps for Domestic Lighting in Developing Countries", Willem M. Floor and Robert J. van der Plas
Click on any of the icons below, or click here for further readings on off-grid lighting; or here for off-grid lighting supplier information. If you wish to go to the next module, click here for the "Pumping Module (Number 2)"of this Guidebook, or click on one of the other modules below. Click here for links to visit some good links to other Internet sites.