Solar lights do not need wiring and are simple to install. A small solar panel charges a bank of AA or AAA batteries, and these power an energy efficient light bulb when the sun goes down. Better circuitry in the photovoltaic cell will produce a brighter light that lasts longer. The brightest solar lights use Light Emitting Diodes (LEDs) instead of filament bulbs.
LED bulbs are not really light bulbs at all, but semiconducting diodes. The light in a diode is produced by excitation of electrons. Since this process does not produce heat, LED lights shine more brightly and last longer. The colour of the bulb is determined by the energy of the excited electrons, and can range from red to amber to bright white. LED bulbs have almost universally replaced filament bulbs in solar lighting.
The amount of energy produced by the solar cell determines how much is available for the light. The DIY Landscape Lighting Guide says that more efficient cells with better circuitry will provide more power to the batteries which will pass that on to the bulb. The batteries will also last longer; some solar lights can remain lit for many nights after one sunny day. The Guide also says that the transparency of the cover on the solar cell is also an important factor as the more light the panel receives, the more energy it can put out.
Nickel-Metal Hydride (NiMH) batteries are often used for solar lights because they stand up better to the frequent charge and release cycle of solar lighting than Nickel-Cadmium (NiCad) batteries. They can also be discarded without harm to the environment. The size and number of these batteries is a factor in the brightness of the solar light. After the solar cell itself, the batteries are the most expensive components of solar lights.
Types of Solar Lights
According to Gardner's Supply Company, there are three types of solar lights. Accent lights are used to highlight parts of a garden to to provide atmosphere. These can be amber or another colour and may include a flicker to simulate the appearance of a flame. They have the lowest light output. Path lights are designed to light walkways and driveways and are mid-range on the light output scale. These often have an on-off switch so that power can stored until it is needed. Task lights or spotlights are the brightest solar lights available and the brightest of these can illuminate with the power of a 40-watt light bulb. They are constructed with special lenses to focus the light, and frequently have detached solar panels that can be placed in a location where there is optimum sunlight.