Photometric Plan

Reading a Photometric Plan

1. Foot candle measurements

On the above plan, there are data points inside the basketball court. These are the foot candle readings calculated at that specific point. Alternatively, the software can calculate lux instead of foot candles.

2. The Fixtures

The fixtures in this example appear as red circles. This gives you a clear indication of where the lights are located over the plan.

3. The Schedule

At the bottom left on this plan is the schedule, The schedule details the fixtures used in the plan. If more than one type of fixture is used, it would be identified in this section.

4. The Calculation

The Calculation Area to the right of the schedule details light levels and distribution ratios. It show the average foot candles in the defined space. It also shows the maximum and minimum calculated foot candle in the plan. The average is the most important of the three, its 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 least light. The best this number can be is 1. 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, lets say the calculation zone included an area outside the court. The avg/min ratio would rise only because min levels would drop.

 

Understanding your area is paramount to developing a good photometric light plan

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. Now comes the painful discovery.

It’s too bright

It’s not bright enough

The light is not uniform

The light is bright under the fixture. Its dark in the areas not underneath fixtures.

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 aren’t all lights basically the same?

Well, the truth is, LED Lighting can be as different as cars in a dealership. Understanding lumens, foot candles and beam angles will help determine the best lighting solution.

But you’re not a lighting engineer. How are you supposed to know all this? You’re not, and that why there are tools that are designed to show you the results BEFORE you purchase. It takes the risk out of purchasing lights.

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 chip sets and crazy beam angles. It may seem like a bargain. Until you install them and realize that you’ve made a big mistake.

 

There can be a huge difference in the light levels and distribution between what appears to be 2 similar fixtures (based on fixture watts). A way to take the risk out of purchasing old “end of use product” is to perform a photometric. We do these for free. Good luck getting your large e-commerce site to do one for you.

How to understand your current light levels

To understand light levels, lets 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 smart phone. A dedicated light meter will give you better results. But its 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 what your current lighting is performing, and your current light levels. But you can also determine:

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.

Understanding Lighting Basics

1. What is a lumen?

A lumen is a unit of light. By itself its useless, but it becomes useful when it defines the collective lumens produced by 1 fixture or bulb.

2. What is a 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) is a requirement that most are looking for when they describe a light level for a project, facility or location.

3. What is a Beam Angle?

A fixture produces lumens. How it is focused requires optics, or the lack of optics. Typically, lights mounted very high require optics to focus the light to where its needed (the ground, for example). However, adding a tight optic to a light and mounting it at a low height produces spotty lighting, with intense bright spots and dull areas in between the lights.

So not having the right amount of lumens and the improper beam angle will provide poor lighting. That is why its important to understand what your foot candle requirements are, and then picking the correct fixture producing the perfect amount of lumens with the optimum beam angle.

Photometrics  Plans – Large and Small

Photometric studies can be done for indoor and outdoor locations, whether its a warehouse, parking lot, baseball field, school gymnasium or office location. They can be developed from CAD files, or for outdoor locations, using google maps.

An Indoor Factory Photometric Study

In this study, 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.

An Outdoor Street Lighting Photometric Study

This is an example of a DOT application, replacing 1500W High Pressure Sodium lights with 600W 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.

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.