As a facilities manager or building owner, you may be wondering how many flood lights you need to adequately light your space. As you can probably guess , there is no straight forward answer as the amount of fixtures for your specific needs will depend on a lot of factors.
The amount of flood lights needed for your space is determined by the following factors.
● The Intensity of the light needed for your space
● The Beam angle or distribution of the light fixtures being used.
● The uniformity desired for your facility.
● The mounting height of your light fixtures
● The placement and spacing for the fixtures selected.
● The angle of the aim of the flood light
The Intensity of the light needed for your space
Intensity is the amount of light energy delivered over a given area. The higher the intensity, the brighter the light will be. Intensity is measured in lux or foot candles. While lumens is the most well known unit of light output, it only applies to the amount of light being delivered by the light fixture. Foot candles on the other hand specifically targets the amount of light hitting the targeted surface.
Understanding this metric is important for selecting appropriate lighting to provide the right level of brightness for whatever purpose or application you wish to use it for.
But how do you know how many foot candles you need?
Unfortunately, it's not that straight forward as there are different foot candles needed for various tasks within different areas of your space. From paying bills in your living room to reading charts and graphs in an office environment, every situation has its own foot-candle requirements.
To determine how much foot-candles are necessary for various applications and tasks, organizations like Illuminating Engineering Society (IES) have created a guideline that provides ideal foot candle levels required for many different scenarios.
While most of the guidelines cover indoor spaces, outdoor spaces also have to take into account the local ordinance requirements which often restricts the maximum amount of light pollution allowed in that area.
To determine the foot candle for your specific applications, it's best to consult with a lighting engineer or electrician who understands not only the lighting needed , but also the local regulations in your area.
How intensity affects the amount of flood lights
Now that you understand what light intensity is, you might want to know how that affects the amount of flood light fixtures needed in a given area.
Typically , higher intensity lights require fewer fixtures to achieve the desired illumination levels. This means if you are using a flood light that has higher lumen output, you may need fewer fixtures than if you were using a floodlight with lower lumen output.
However, all the other factors mentioned in this article will have an impact on light intensity and may cause you to increase or reduce the amount of light fixture to get the right amount of light output or intensity.
For example if you're restricted to a low mounting height for your light fixture, your flood light might be too intense for the space and decrease the total amount of light needed for the whole area.
Another common restriction is the uniformity requirements. You might need to add extra flood lights to your space to fill in the gaps where the intensity is too low. You might have heard these referred to as dark spots. Dark spots are simply a lower intensity area relative to the overall lighting of the space.
The Beam spread or distribution of the flood light fixture being used.
Flood light fixtures are designed to spread light over large areas, making them ideal for lighting up large outdoor spaces. The spread of the flood light- commonly known as beam spread- depends on two factors: the Vertical illuminance & the Horizontal illuminance.
The horizontal illuminance is the amount of light falling on a horizontal surface , while vertical illuminance is the amount of light reaching a vertical plane like a wall.
The National Electrical Manufacturers Association (NEMA) has come up with a standard to calculate the beam spread of any flood light fixture.
The NEMA beam spread classifications categorize the various beam angles into 7 categories and assign a number to each range. Narrow beam spreads (10° - 18°) are given a Type 1 designation, while very wide beam spreads (130° + ) are called a Type 7.
Each flood light fixture is assigned 2 types. One for the horizontal, and the other for Vertical. Some Manufacturers indicate this with an H or a V on their spec sheet, while others assume that the customer should know the placement for each number.
For example a beam spread could be written as 7H6V or just simply 7x6.
It's important to note that the wider the beam spread, the shorter the distance should be between the flood light fixture and the targeted surface. Narrower beam spreads are used more for spot lighting and longer distance between the fixtures.
How does Beam Spread impact the amount of flood lights you need
Because beam spreads affect the total area covered by a single flood light, your choice of beam spread will also naturally affect the amount of fixtures you need to light up a given space.
If your selection mainly contains narrower beam spreads, you will need more of them to cover a given space. Less fixtures will be required for wide beam spreads.
As we mentioned earlier, the beam spreads also affect the mounting height required. Wider beam spreads can't be mounted too high. Therefore in an instance, where the fixtures can't be mounted too low, you might be forced to go with a narrower beam spread. This would mean you need more fixtures to get the right amount of illumination.
The uniformity desired for your facility.
Light uniformity refers to the evenness of the light intensity. In other words, it's how evenly distributed the illumination is over a given area.
The goal when lighting up a space with flood lights is to avoid dark spots, or areas of lower light intensity than others. You want your space to feel safe and have an area that's welcoming to users and discouraging to intruders.
To achieve ideal light uniformity, lighting designers and engineers look at required uniformity ratios. This ratio compares the area with the highest light intensity to the lowest intensity area. For example a light uniformity of 3:1 is a well uniformed outdoor space.
How light uniformity affects the quantity of flood lights needed
The uniformity desired for your space will have an effect on all the factors mentioned in this article including mounting height, intensity, beam spread etc... As a result, this will in turn have an effect with the amount of flood lights needed for this space.
A common example is when installers are encouraged to include more than one fixture on a single pole not to increase the intensity but simply to make the space look more uniform. When light fixtures are spaced too far apart, they create dark spots which can sometimes fall below the low intensity minimum designated for the specific application. In that instance, it's best to increase light fixtures to fill the space.
Sometimes, the placement of poles and light fixtures might be restricted to specific areas, which can cause the installer to install fixtures of the different beam spreads on the same pole in order to meet the uniformity requirements.
The mounting height of your light fixtures
Mounting height is an important factor to consider when selecting your flood lights. It will determine the amount of light reaching a particular surface and how that light illuminates its surroundings. Generally, larger beam spreads require lower mounting heights while narrower beams work best with higher mounting heights.
Another interesting note is that the general rules of thumb use mounting height as a multiplier to gauge how far fixtures should be spaced apart from each other. For example a Type 3 fixtures projects forward about 2.5x the selected mounting height.
How Mounting Height affects the number of Flood light fixtures needed.
Since mounting height is one of the most important factors in determining how far a beam of light will project out onto the target area, it has a major impact on the number of light fixtures selected for your outdoor space.
Increasing the mounting height will often require more fixtures in the space or an increase in wattage for a more powerful light output. It's up to the installer to weigh the impact on the overall design and cost of the project.
The placement and spacing for the fixtures selected.
As you would expect, placement and spacing of the fixtures is a major player when it comes to the number of light fixtures needed for your outdoor space. Oftentimes, changes have to be made both placement and the space between fixtures depending on the other factors we discussed today.
However, sometimes the placement can't be changed and the ability to meet ideal spacing requirements is limited. This is when the lighting designer has to be creative and change some other aspect of the project to make it work.
How placement and spacing affects the number of fixtures needed
Spacing fixtures close to each other will increase the brightness of any given area, while setting them far apart will introduce more dark spots. However, there comes a time when light fixtures might be too close to each other and cause a lot of glare.
As previously mentioned, knowing the beam type and the overall foot candle projection, will go a long way to striking the right balance of ideal lighting and correct spacing.
For placement of fixtures, it's mostly recommended to space flood light fixtures along the side of the space. However, there comes times where that can't be done and these fixtures might need to be placed at the corners or other unwanted places. This is when the installer can get creative by selecting light fixtures that project forward a little bit more or increase the amount of flood lights on a single mounting point.
The best way to determine how many flood lights you need for your space
Given the fact that there are several factors that affect the number of flood lights for your space, the best way to determine how many units you will need for your space is to lean on the experts and guidelines.
General rules of thumb are great for projects that don't require a lot of design input and just need to be done. This could be your own personal garden , or a simple landscape lighting project.
However for larger scale installations, it might be best to consult with a professional lighting designer who can assess the space, take in account all the factors mentioned above, and provide an accurate assessment based on this criteria.