What is a Photometric Lighting Plan?

One of the biggest challenges of buying new lighting or upgrading to LED lighting from existing fixtures, is anticipating how your new lights will look and function in your space. Luckily, there is a solution. A Photometric Lighting Analysis is a way to view a proposed lighting solution over a given area. Using photometric software, you can model an indoor or outdoor room or the area’s layout. The software can also import existing layouts and CAD designs.

Lighting engineers can input fixtures at specific locations, angles, orientation and height. The software calculates light levels and provides a comprehensive visual layout report. The report displays calculation points representing the foot candle reading at that location.

How to Read a Photometric Lighting Analysis 

Although they are indispensable tools, a photometric lighting plan won’t do you any good unless you know how to read it.

When you receive a LED Lighting Supply photometric plan, you’ll notice that there is a lot of information to review, and you’ll need a little bit of background knowledge to get the most out of it.

Below are some terms to familiarize yourself with before you take a look at your lighting plan. Keep the below image in mind as you read about each of these. 

Indoor Basketball Court Lighting Calculation

Foot Candle Measurements

A foot-candle represents the amount of light that reaches a surface area, and it’s measured in lumens per square foot. In the above plan, you’ll see that there are several data points inside the basketball court. These represent the foot-candle readings calculated at those specific points. And if you’d rather look at the layout in meters, the software can also calculate lux instead of foot-candles.

The Fixtures

The light fixtures, arguably the most important thing on a photometric lighting plan, are shown as red dots. This will give you a clear indication of exactly where the lights are located in the plan, and where they should be in real life.

The Schedule

This is an extremely important part of a lighting plan that is often overlooked. The schedule is found at the bottom left of your lighting plan. It details the At the bottom left on this plan is the schedule, The schedule details the fixtures used in the plan, and if more than one type of fixture is used, they will all be identified here.

The Calculation

This is where some of the most valuable information in the lighting plan is found. The Calculation Area, located to the right of the schedule, identifies the light levels and distribution ratios of the fixtures outlined in the schedule. It shows the average foot candles in the defined space as well as the maximum and minimum calculated foot candles in the plan. 

The average is the most important of the three, it’s the target foot candle reading for the project. The next two numbers are as important. The Avg/Min ratio is the ratio of the average foot candle reading to the minimum calculated point. The best this number can ever be is 1.

The Max/Min ratio is the ratio of the brightest location to the one with the least light. This helps to predict problems with light distribution. The best this number can be is 1, and it is almost always a higher number than the Avg/Min ratio. Targeting an avg/min ratio between 2 and 3 is ideal. The higher this number, the more ‘spotty’ your lighting will be. It’s important to note that a well-defined calculation zone needs to exist. Using the above example, let’s say the calculation zone included an area outside the court. The avg/min ratio would rise only because min levels would drop.

By familiarizing yourself with the above terms, you’ll be able to effectively read your photometric lighting plan, and design a lighting layout that works well for your specific facility.

However, even if you feel comfortable reading a photometric lighting layout, questions may still arise. If you have any issues, questions, or concerns, feel free to reach out to one of our lighting specialists. 

The Difference A Photometric Lighting Analysis Makes



Inadequate Light Levels or Spotty Distribution

This is a huge problem in the lighting industry. Facilities are looking to convert to LED lighting, so they go online to a large online retailer and look at the products offered. They make their best-educated guess at what light they should use, purchase it, and install it, only to find that it’s not what they were wanting at all.

It’s too bright

It’s not bright enough

The light is not uniform

The light is bright under the fixture.

It’s dark in the areas not underneath fixtures.

And this is exactly why we always suggest using a photometric lighting plan. Because, how were you supposed to know what the outcome was going to be? After all, the light appeared to be exactly what you needed, and most suppliers seem to suggest that all light fixtures are basically the same. But the truth of the matter is that depending on the layout of the area, what lights you choose, how you install them, how high they are installed, and the surrounding environment, LED Lighting can be as different as cars in a dealership.

The only way to accurately predict how your lights will look is to have a complex understanding of lumens, foot candles, and beam angles. But you’re not a lighting engineer, and like most facility managers, you likely don’t have the time to teach yourself everything you need to know about lighting. And, that’s where the photometric lighting plan comes in. A photometric lighting plan takes everything into account and does the math for you so that you can make an informed lighting purchase, whether or not you’re a lighting engineer. 

The issue with buying “Off the Shelf” lights from large e-commerce sites is you have no idea what you’re buying. A lot of time manufacturers will dump old inventory on these sites, with old chipsets and crazy beam angles. It may seem like a bargain, but you’ll quickly realize that you’ve made a huge mistake.

Understanding Your Current Light Levels

You can’t understand where you’re going if you don’t understand where you’ve been. Alright, that’s not exactly how the saying goes, but it does still apply here. In order to understand light levels let’s introduce the concept of foot candles or lux. They are basically the same thing, light measurements.

Readings can be taken using a simple light meter or a light meter app installed on a smartphone. A dedicated light meter will give you better results. But it’s OK to use a free light meter app to get an understanding of the light in your location.

For example, you may have a production facility and are looking to upgrade to LED Shop Lights. A good process would be to install a light meter app on your phone and use it to take several readings around your facility. Go under a light, go-between lights, go into the center of the space, go to the edge, and take readings.

From this, you will get a good idea of how your current lighting is performing, and your current light levels. But you can also use this method to determine things like:

Are my light levels OK, too bright or too dim?

Are my light levels pretty uniform and evenly distributed?

Would I like to improve the light levels, or are things OK

Lighting Terms 101

The cheat sheet for everything you need to know in order to be an expert on your lighting. 

 Lumen –  A lumen is a unit of light. By itself it’s useless, but it becomes useful when it defines the collective lumens produced by 1 fixture or bulb. It is the amount of visible light that a fixture emits. 

Foot Candle –  A foot-candle is a measurement of light at a specific location, and 1 to many lights can contribute to the specific foot candle reading at that location. Foot candles (or its equivalent LUX) are the requirement that most are looking for when they describe a light level for a project, facility, or location.

Beam Angle -The beam angle of a lamp is the angle at which the light is distributed or emitted. This can be done with additional optics, or as is the case with LEDs, by engineering the light in a specific way. LEDs have an extremely large range of available beam angles. 

LED Photometric Lighting Plans

Indoor Factory Lighting Plan

In this light plan, the customer’s current lighting was averaging around 12-foot candles. They approached LED Lighting Supply for an upgrade to LED, but like most large customers, wanted to take the first step and perform a light analysis.

They wanted more light, they wanted to save energy, and they were tired of changing out bulbs and ballasts.

The customer provided LED Lighting Supply with a CAD file (.dwg file) and we imported it into our software.

We modeled 1 area, replacing their HID lighting with a combination of 120 Watt and 200 Watt LED High Bays.

In the main work area, we increased their foot candles from 12 to 41! Average Min Ratio of 2.31 indicates uniform light levels throughout the space.

Outdoor Street Lighting Plan

This is an example of a DOT application, replacing 1500 Watt High-Pressure Sodium lights with 600 Watt LED High Mast Area Lights with 150-degree optics.

The ISO-lines represent foot candle transitions, with the red-line highlighting 0.6 foot-candles.

LED Lighting Supply took scaled images from Google Maps to create an outdoor photometric plan.

 Photometric studies allow customers to see how the lights will perform before having to commit, and allows for the lights lumens and optics to be adjusted to meet the specifications or desired amount.

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What is a photometric plan?

A Photometric Lighting Analysis is a way to view a proposed lighting solution over a given area. Using photometric software, you can model an indoor or outdoor room or area layout. The software can also import existing layouts and CAD designs. Lighting engineers can input fixtures at specific locations, angles, orientation and height. The software calculates light levels and provides a comprehensive visual layout report. The report displays calculation points representing the foot candle reading at that location.

How do you do Photometrics?

Photometrics are done by using software specifically designed to create lighting plans. The software allows you to define specific indoor or outdoor spaces, import light fixtures, and then place these light fixtures on the model. The software then calculates the amount of light at specific points in the model along with how well the light is distributed.

How do you read a lighting plan?

A light plan will show you a model of your area and the location of the fixtures. It then has points in the model that shows you foot candle readings at that point. Also included in the model are average, maximum and minimum foot candle readings. Also included is distribution levels – a definition of how well the light is distributed within the model. A good design will have avg/max distribution levels under 3.0.