Ask the right questions to find the best outdoor solar lights for your site
Solar bollard lights are perfect for outdoor lighting and landscape design—they are simple and inexpensive to install, environmentally friendly, and they don’t add to your monthly electric bill. The growing market for solar has driven a lot of product innovation, but it also means that customers are often new to the industry, and have no idea what to look for when comparing models.
Different solar lights have widely varying levels of quality, on everything from power storage capacity to light output and service life. Asking the right questions prior to purchasing will save you from wasting money on an ineffective solar installation.
Most people understand the general principle of solar lighting: sunlight on a solar panel charges the battery during the day, and that stored energy is used to power the light after dark. The greater autonomy a solar light has, the longer it can remain lit without being charged.
Bottom-tier solar lights have cheap batteries, so they can only stay brightly lit for a few hours without direct sunlight. That might not be a problem in the tropics—where the sun shines consistently year-round—but it makes the lights completely ineffective anywhere else.
To be effective in the northern latitudes, solar lights need more autonomy. Better solar lights come with a high-capacity lithium battery, and use their stored power more efficiently to stay lit during long periods of dark and stormy weather.
2. Power Storage
Autonomy is important, but the related stat of power storage is a close second; it measures how efficiently a solar fixture can convert sunlight into battery charge. A solar light with good power storage requires less time to fully charge a depleted battery, and can continue to operate effectively with few daylight hours.
Power storage isn’t the same as charging time. A low-capacity battery might reach full charge more quickly than larger battery, but the high-capacity battery will usually have a superior power storage rate.
3. Working Temperature
Some climates are harder on outdoor solar lights than others. Moisture mixed with the extremes of hot and cold can wreak havoc on poorly protected batteries and solar cells. If your site is especially wet, hot, or cold, commodity level batteries probably won’t survive it for long.
You can make sure your installation will last by selecting solar lights with a specified high or low temperature tolerance. The battery is usually the first thing to fail from extreme temperatures.
4. Luminous Flux
Luminous flux describes the amount of light output that a lighting bollard provides. It is measured in lumens. Low-quality solar lights are notoriously dim. LED lights are good at providing maximum lumens with minimum power, but they can only do so much with a limited power source. Less expensive models may produce under 100 lumens, while high-performance models can consistently produce over 120. If your solar bollards produce on the lower end, you probably be forced to compensate by installing them at more frequent intervals. More bollards may end up costing the project, depending on total path size.
Every lighting system will provide light at differing points of illumination throughout its distribution pattern. This means that light will appear more intense at certain points of distribution than others and different distribution patterns will deliver light at different levels of intensity. For most solar bollard lighting applications, the average and minimum illuminance values and the maximum to minimum uniformity ratio for the area to be illuminated are of the most interest. IES files that can be used to determine if these bollards will meet the illuminance requirements for a project are usually available through the solar bollard light seller.
6. Light Color
Lighting color is measured in Degrees Kelvin, with different temperatures providing different colored light. LED lights with lower Kelvins appear warm, like candlelight or incandescent lamps. Neutral daylight-like LEDs are 4000-5000K. LED bollard lights in the 6000-7000K range cast their surroundings in a cold, icy blue.
As the lighting color most similar to daylight, neutral light is the most common LED light option. Warm light creates a softer ambience and is often used in landscaping and decorative applications. It offers the advantage of more effectively conserving power than other colors, as cooler temperature lights are more efficient than warmer ones.
7. Solar Insolation
Solar insolation refers to the amount of sunlight that a solar bollard receives in one day. A site’s region, weather patterns and shading will all affect the level of solar insolation that the bollard’s solar cells receive. Solar bollard lights with good power storage can operate effectively with 4-5 hours of unobstructed sun exposure, preferably for the middle part of the day. Ideally, this means that the bollards should not be subjected to any form of shade between the hours of 10 am and 2 pm.
If the site has intermittent shade, there are models available that separate the solar panel for the solar-powered LED light. While such models are a little more inconvenient to install because they require some trenching, they do allow solar lighting in areas that would otherwise have to be connected to electric utility lines.
8. Dark Skies
Dark skies is an initiative to reduce light pollution. Many fixtures are designed to minimize light pollution by deflecting light where it is most useful—the ground. They are categorized as “cut-off” fixtures, which, means that less than 2.5% of the light output is allowed to escape the fixture above 90 degrees. Cut-off lights contribute positively to a site’s lighting performance except in the areas required to be darkest, under the LEED rating system.
However, "beacon" lights that do not have a cut-off are also useful in lighting design. These help define path borders and work as wayfinding devices.
9. Light Distribution
Lights are commonly offered in two distribution patterns: symmetrical and asymmetrical. Symmetrical lighting bollards deliver light in a condensed, even circular pattern while asymmetrical lighting bollards deliver light in a narrow, elongated form that is ideal for pathway lighting. Symmetrical lighting is generally used in in landscaping applications while asymmetrical lighting is used to brighten walkways in safety applications.
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