There are three important points to consider
when choosing and installing lights:

• The amount of visible light the lamp produces
• The amount of electric power required by the lamp
• The direction in which the light shines

While this all sounds very obvious, we are mostly used to living in an environment where electricity is plentiful and lighting is as much cosmetic as functional.

Efficient lighting involves a slightly greater initial investment but gives savings in other system costs, extends the potential of the system and gives a superior quality of light.

Keeping rooms as light (in colour) as possible, and maximising natural lighting will reduce lighting demand and improve overall lighting efficiency.

When a lamp is in use it produces both heat and light. Visible light produced by a lamp is called the luminous flux; the amount of visible light a source produces is measured in lumens (lm).

The rating of an electric lamp is always given in watts. An 8 watt fluorescent lamp draws 8 watts of electric power. Efficacy is a special term, which tells how much light (in lumens) is produced per watt of electric power. Lamps with a high efficacy produce more light energy watt of power than lamps with a low efficacy and are therefore more desirable in a solar powered property.

The table below shows some typical luminous flux, and efficacy values.

Light radiates from a bulb in all directions, but it may only be needed in one direction. For reading the light should shine on the pages of the book and not on the ceiling. Light efficiency can be improved by using reflectors to direct the light where it is needed.

Low Voltage Lighting

Fluorescent

Fluorescent lamps have high efficiencies of between 30 to 75 lumens per watt. An 8 watt tube lamp has an efficacy of between 30-40 lumens per watt, while a 13W lamp has an efficacy of between 50-60 lumens per watt. Tube lamps have long life times of between 2000 and 5000 hours. Most solar electric lighting systems choose fluorescent lamps in places where light is required for lengthy periods of time. When operated on a direct current (DC) system, all fluorescent lamps require a ballast inverter to modify the power.

Several types of tube lamps are available. The most common type, the batten lamp, is a straight tube fastened to a fixture in which the ballast is contained. The compact or 'PL' type fluorescent, which has a tube bent in a 'U' shape is a more efficient lamp and displays a more complete light spectrum which is brighter and warmer than the batten lamp. Although 'PL' fluorescent lights are more expensive, it is usually worth the extra cost in terms of better light output.

Halogen

Halogen lamps are a special type of incandescent lamp with filaments that produce a 40 to 50% brighter light than regular globe lamps (up to 30 lumens per watt) The lamps last about twice as long as conventional incandescent lamps. Halogen lamps may be sold with built in reflectors, which direct light where it is needed.

LED lamps

LED or 'light emitting diodes' are the most efficient form of electric lighting when the life cycle of the bulb is considered. They have power consumption in some cases of less than 1 watt and have a 100,000 hour rated life. LED lamps are three times more efficient than halogen lamps and perfect for low level and localised lighting. LED lights can be used directly on solar system without any ballast

Performance of Typical 12 Volt Lamps

Using low voltage lighting run directly from the battery store not only saves the cost of using an inverter but is also more efficient since low voltage bulbs give more lumens per watt than equivalent 220V bulbs.

Using efficient lighting allows you to:

• Fit smaller systems, while achieving good light levels
• use light for longer
• Increase the number of lights in the system
• Have spare power for extra equipment