Understanding UW Light Specs & Testing

December 4, 2014

I. The Problem: Few manufactures test their lights to established standards, or publish accurate lumen and beam angle specifications. Calculated values based on the individual LED specifications are easy to generate but often highly inaccurate.  Without testing to recognized standards, the user cannot accurately compare different lights or evaluate the quality and performance of their purchase.

The solution is for manufacturers to adopt and adhere to widely accepted industry testing standards and to make this test data available to consumers.

II. What Standards are currently used to test lights?
1. The ANSI/NEMA FL-1 standard is a nationally recognized testing methodology designed to ensure accurate and consistent data for lumen output, water ingress, and run times. We use the FL-1 standard to test all our lights. (Go to any light on our website and scroll down to access the lumen & beam test results).

2. To measure light output the standard uses the “Full Width at Half Measure” or FWHM value for defining the radiated power and beam angle.

III. How Do You Evaluate a Light’s Beam Angle and Performance?
1. We run tests to measure the FWHM output values of all our lights.  This is method is suitable for a symmetrical optic with its maximum intensity in the center.

The FWHM test measures the beam width where the light intensity has dropped to half the maximum value measured in the center of the beam. This reduction in light intensity represents a full camera exposure stop and any objects beyond this beam angle are going to be increasingly under exposed.
So a light might be described as having a wide beam angle, but if the intensity of the light is not defined at those angles, then it may not be of any use to the photographer.

2. To test our beam angles we measure the light output in increments of 2 degrees. We use the data collected to create polar graphs showing the light output verses beam angle. The point where the plotted curve intersects the 50% ring determines the half angle. These curves cross the 50% ring in two locations, the sum of the two half angles is the FWHM beam angle*.

By faithfully measuring our lights to recognized industry standards and publishing our test data the end user can know that our lights will perform at the stated specifications.

*The widest FWHM beam angle in water we have measured of any lights on the market is 90 degrees.

IV. How Does Water Effect Beam Angles?
The Law of Refraction states that when light passes through a media of different refractive indices such as air to water, it changes the angle of the light. Since light travels slower through water than air, the light from a single source will become more focused. There is a 33% loss of the beam angle (becomes more narrow) when lights are used in water verses in air. So a light that has a beam angle of 100 degrees in air (FWHM) will only measure 67 degrees in water.
UWTestingPhoto3 Many manufactures overstate the beam angles – they may claim a 100-degree beam angle but when we actually measure the FWHM we may get a beam angle in water of 37 degrees.  In other words if the manufacturer doesn’t specify that the beam angle is measured in water and that the testing was conducted based on recognized standards then you can’t know what the light will actually do in water.

V. How Is Beam Consistency and Runtime Measured?

Consistent lumen output is key for high-quality video and photography. Using an integrating sphere, the actual lumen or light output and run-time is precisely measured using certified equipment. The lumen output is the total amount of light across the entire beam pattern (not just how bright it is in the center).

To see how an Integrated Sphere works: http://www.youtube.com/watch?v=mvyptpA-BmY to see our test data from the sphere: https://www.lightandmotion.com/choose-your-light/sola-imaging/sola-video-2500

In regard to runtime the question is not “how long will my light stay on” but “how long will my light run at the constant maximum output?” The graph below compares the Sola Video 2500 to ITorch Video Pro. The Sola maintains 2500 lumens for over 60 minutes (Light & Motion states a 60-minute run time).

UWTestingPHoto5VI. What is the responsibility of the dealer & user?    
In a market that is not monitored by legal regulations it is critical that dealers and consumers understand how lights are measured and tested. Until all manufactures adopt accepted standards for testing and publish the findings, consumers will need to be proactive in asking how the beam angle, lumens, and runtimes are tested to ensure the highest quality purchase.