Commercial Solar Lights: Guide to Watts, Lumens and Foot Candles – Part 2 – What’s Important When Choosing Your Commercial Solar Post light

In Part 1 we discussed the differences between Watts, Lumens and Foot Candles (or Lux used in the metric system). We showed that Watts is a unit of power measuring how much energy a light source is using to power the light. We mentioned that using Watts to evaluate a light’s brightness is not ideal as some lights are more energy efficient than others, like the LED for example, using less Wattage.

Lumen is the term used to describe the total amount of light emitted by a light source. However, to understand how much light actually ‘falls’ on the surface we should use Foot Candle to measure how effectively a surface is being lit (1 Foot Candle= 1 Lumen per square foot). Two lights with the same lumens can light surfaces differently, depending on several factors such as the height of the light, its angle, etc.

If you really want to understand how much light you can expect on the surface, we recommend using Foot Candle as the relevant metric (or Lux if the metric system applies).

But how much Foot Candle is enough?

Required Foot Candle for Pedestrian Lighting

In general, the required Foot Candle in public areas is to be determined by the local municipalities. However, the range may be consistent. Here are some real examples of different foot candle requirements from official bodies:

• The city of Sandy Springs, GA requires street lighting for pedestrian streets to be 0.5 Foot Candle.(source: Sandy Springs, Georgia – Technical Manuals SECTION 9 – LIGHTING AND UTILITIES )

• Freeway lights should be: 0.5 Foot Candle. Source: here
• Intersection lights: 1.3 Foot Candle. (Source: Roadway lighting’s effect on pedestrian safety at intersection and midblock crosswalks.)
• Pedestrian bridges and similar pedestrian walking paths: 0.46 Foot Candle

A study examined the relationship between illuminance and freeway crashes looking at day/night crash rate ratios for lit and unlit roads. The research found that roads with the lower range of illuminances (3.2 lux to 6.4 lux = 0.3-0.6 Foot Candle) had a lower night/day crash ratio than roads with a higher range of illuminances (8.6 lux to 11.8 lux (=0.8-1.1 foot Candle) and 14 lux to 16.1 lux = (1.3-1.5 Foot candle)). As a result of this data, the research recommended a level of 5.4 lux for freeways (=0.5 Foot Candle). A result where a higher lighting level increase the crash rate ratio may be surprising. It must be remembered that additional lighting can create additional glare and can impact the driver’s adaptation level. While this result is not expected, it may be justifiable. (Source: Road lighting research for drivers and pedestrians: The basis of luminance and illuminance recommendations, Jan 9^th, 2018)

So, 0.5 Foot candle is usually what is required to illuminate high traffic areas, but how do we know how much Foot Candle does a certain light generates? The answer is usually looking at the light IES file.

What Is an IES File?

IES is derived from the acronym Illuminating Engineering Society. An IES file is a great source to learn how much light you can expect from a specific light. IES files are standardized data files, usually provided by a 3^rd party, that expresses the light output of a light as luminous intensity along with descriptive and documentary test information. Usually, an IES file for a certain light will show the foot candle (or Lux) of the light per different heights the light may be installed in.

When considering a commercial lamp post in general and a commercial solar post light specifically, ask to see the IES file and check the expected Foot Candle expected at the planned height the light will be installed at.

Foot Candle for Gama Sonic Commercial Solar Lights

Now that we know the Foot Candle is the most accurate metric for determining how intense lighting will be in a specific area, how much Foot Candle does a commercial grade solar light from Gama Sonic generate? This will vary from one light to another. You should start by discussing your needs with the commercial lighting manager you’re working with. Do you need it to light up a high traffic pedestrian area? Do you only want it to provide a nice ambience? These questions and others will matter.
Let’s take a look at the Gama Sonic modern commercial solar LED post light with motion sensor and time (GS-102), for example. This is a powerful, durable, and beautiful commercial grade solar lamp post designed for high traffic pedestrian areas such as parks and streets. The GS-102 IES file (remember, The IES file is a standardized data generated by a neutral 3^rd party) will show the light spread – Foot candle and Beam Width – on the ground at different heights.

In this actual table from the IES file of Gama Sonic Modern commercial solar LED light (GS-102) you can see that installing the light at a 12 ft. height (10 ft. pole + 2 ft. height of the light fixture itself) falls between the 3m/9.8ft and 4m/13.1ft marks, generating an average of at least 1 Foot Candle and up to 1.66 Foot Candle , which is 2X-3X than the recommended Foot Candle for high traffic pedestrian pathways.

This following real application image taken in a community park in Mebane, North Carolina demonstrates how the light spread looks when this light is installed on a 10ft pole.

Now that we know how to determine the intensity of a light by using the most accurate metric to compare commercial solar lights by, it’s time to choose the commercial solar light that’s best for you! Contact us to discuss your commercial lighting needs so we can discuss the right Gama Sonic commercial solar light for you.