Solar Lighting Glossary

Learn the photometric principles that can be used to maximize the efficiency of your solar bollard lights.

What is Photometry and why is it important in lighting bollard applications?

The term photometry refers to the scientific measurement of light and photometry is a process in which characteristics of light are measured. Photometrics are of particular importance in solar bollard applications as they measure how bright a light will appear to onlookers and the level of visibility that solar bollard lights will provide on a given site. Photometric performance plays a significant role in the level of visibility on the site in nighttime environments as well as how efficiently a solar powered bollard will operate in a particular environment. Proper placement of the solar bollards and the selection of a proper lighting fixture will ensure proper photometric performance and that an adequate level of safety and security is provided. Photometric performance can be measured in several different ways and several photometric principles should be taken into consideration when designing a bollard lighting project:

Lighting Distribution

When examining photometric performance, it is necessary to understand lighting distribution. Light emitted from a solar bollard light can be delivered in different patterns and Reliance Foundry offers models that distribute light in two patterns: symmetrical and asymmetrical. Symmetrical lighting bollards deliver light in a condensed, even circular pattern. They are commonly used in landscaping applications or to brighten medians and contained areas. Solar bollard lights with an asymmetrical distribution pattern deliver light in an elongated form that makes them ideal for pathway lighting. The following diagram demonstrates how light from both patterns will fall on the surface surrounding a lighting bollard:

Chart showing symmetrical and asymmetrical light distribution options
Select lighting distribution at time of order.

Luminous Flux

Luminous flux is a measurement of the overall light output that a solar bollard provides. Luminous flux is measured in lumens and can provide an indication of how effective the illumination of a lighting bollard will be. Along with lumen output, it is also important to consider where the lumen output will be distributed. As previously mentioned, symmetrical and asymmetrical distributions are effective for different applications. With a typical lumen output of 200-300, Lighting Bollards by Reliance Foundry provide an industry leading level of solar-powered luminous flux.


Illuminance is a measure of the illumination provided by a solar bollard light at various points throughout its distribution pattern. Light emitted from a solar bollard will appear more intense at certain points of distribution than others and different distribution patterns will deliver light at different levels of intensity. This means that light emitted from these differing patterns will often appear more intense at certain points of distribution than others. As discussed above, lighting bollards provide light in symmetrical or asymmetrical light distribution patterns and each offers a different illuminance. Footcandles (lm/ft²) is the unit of measurement used to calculate the luminance cast on a surface by a one candela source one foot away. The following diagram demonstrates the differing points of light intensity throughout Reliance Foundry’s symmetrical and asymmetrical lighting distributions.


Lighting intensity measured in foot candles


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. Developing a lighting layout that takes both of these values into consideration will ensure that an adequate level of light will be provided and that there will be no breaks caused by lighting level drops. To obtain the minimum illuminance value and maximum to minimum uniformity ratio of your site, you may wish to consult a lighting specialist, engineer or architect. Independently-tested IES files are available. Please contact the Reliance Foundry Sales Department for more information.

Solar Insolation

The term solar insolation refers to the amount of sunlight that a solar bollard receives in one day. It is commonly measured in the amount of hours the bollard’s solar panel will be directly exposed to sunlight. The amount of sunlight light the bollard will receive will determine the level of power the bollard will have to operate. The less sunlight a lighting bollard receives, the less energy it will have to operate.

Typical solar lighting bollards will deliver light at full capacity until all stored energy has been consumed. Reliance Foundry’s solar-powered lighting bollards, however, constantly measure and predict weather patterns. They are proactive in energy management and wisely expend energy in a manner that helps to ensure that they are able to perform throughout the night. In areas or at times of year with less solar insolation, Reliance Foundry’s solar-powered lighting bollard’s intelligent energy management system (EMS) allows it to provide light where competitive lighting bollards cannot.


Depending on the area in which a lighting bollard is installed, there may be days when it does not receive solar insolation. Days in which the solar bollard does not receive sunlight are known as “no-sun days.” Because solar bollards operate with a battery that stores energy, they are able to function on no-sun days. This process is known as “autonomy.” Most solar lights will operate at full capacity until all of the battery’s power is expended but Reliance Foundry’s solar lighting system predicts weather patterns and conserves energy accordingly. The intelligent lighting system will ration energy to ensure that it will continue to operate throughout the night. With less solar insolation, there will be less light output. In a worst case scenario, that in which the bollard receives no light, the lighting bollard will operate at minimum capacity that will still allow for 14 days of autonomy (based on a 16 hour night)! Given the adaptive capabilities of the bollard’s lighting system though, autonomy is always varying with the goal of maintaining enough energy to operate in the prevailing conditions. In a typical location, this means the solar bollards will have more autonomy in the winter than in the summer.  In a place like Seattle, solar bollards may have as little as 3 days autonomy in the summer and over 14 days in the winter.

Please note that it is necessary to judge the solar insolation that a site receives prior to installation. Each site is different and, although Reliance Foundry’s solar bollards expend energy efficiently, certain base levels of solar insolation are required to ensure that they operate effectively throughout the year. Northern environments should pay particular attention to the average number of no-sun days experienced. Shading, at any site may also affect a solar bollard’s ability to receive sunlight and thus its autonomy. If you have question on the typical levels of solar insolation you region receives and if your site can facilitate the use of solar bollards, please contact the Sales Department.


The term “dark sky” refers to efforts to reduce light pollution. Light pollution derives from light that is delivered ineffectively or in an uncontrolled manner. Reliance Foundry’s solar bollard lights are categorized as “cut-off” fixtures. Cut-off lighting fixtures control light delivery so that less than 2.5% of the light output is allowed to escape the fixture above 90 degrees. This means that Reliance Foundry’s solar bollards deliver light in a highly efficient and effective manner. Cut-off lights contribute positively to a site’s lighting performance except in the areas required to be darkest, under the LEED rating system. For more information on how lighting design can help a project qualify for LEED credits, please visit the US Green Building Council’s guidelines on light pollution reduction.

Reliance Foundry’s Solar-Powered bollards are designed to conserve energy, reduce light pollution and increase safety and security. Photometric planning, however, plays a key role in the success of every lighting bollard application. In order for Reliance Foundry’s Solar-Powered Lighting Bollards to provide an industry-leading performance, the selection of an appropriate lighting fixture is necessary and adequate evaluation is required. When properly employed, Solar-Powered Lighting Bollards efficiently illuminate streetscapes, increase safety and heightens a site’s aesthetic appeal. Taking key photometric principles into account will aid in the selection of a lighting bollard by Reliance Foundry that performs to the highest standards.