Followspot Photometric Testing: Real-World Measurements for Followspots

Followspot photometric testing is essential for setting accurate expectations about how a followspot will perform in a real venue. At Canto USA we measure light intensity from our fixtures in real performance environments so venue managers, designers, and operators can rely on the published numbers. ReFollowspot photometric testing is an important part of understanding how a fixture will perform once it is installed in a real venue. A specification on paper can tell you a great deal about a followspot. Still, designers, venue managers, dealers, and operators also need reliable information on how much light a fixture can deliver at realistic throw distances.

At Canto USA, we use photometric testing to measure light intensity and document followspot performance under controlled conditions. The goal is to give customers useful numbers they can reference when deciding whether a particular followspot is appropriate for their space.

One example of that process was our testing of the Canto Tango followspot series at the U.S. Cellular Center in Asheville, North Carolina. By conducting the tests inside an actual performance facility, we collected measurements at realistic distances while controlling variables that could affect the results.

Below is a closer look at how we gathered, reviewed, and prepared those photometrics for publication.

Why Real-World Followspot Photometrics Matter

Photometric data helps answer one of the most basic questions a customer has when evaluating a followspot:

Using a real performance space gives us room to establish longer throw distances and better represent the conditions in which these fixtures are normally used.

The goal is not to create the highest possible reading. It is to collect data that realistically reflects the fixture’s intensity, beam size, and useful operating range.

For more information about how a followspot is used once it is in the venue, see The Art of Followspot Operation.

Establishing a Repeatable Testing Process

Good photometric data depends on consistency.

If one reading is taken under one set of conditions and another under a different setup, comparing the two becomes much less useful. That is why Canto USA follows the same basic process throughout a followspot test.

For the Tango test in Asheville, we first marked out each test distance and set up the fixture. As we changed settings, we recalibrated the meter and took several readings at each mark.

Taking several readings instead of relying on one measurement also helps us identify anything unusual before we publish the final numbers.

Distance Measurement

A laser distance meter was used to establish the test distances.

Tape marks were then placed at each measurement position so every reading could be taken from the same location.

For this test, measurements were taken at:

• 100 feet
• 125 feet
• 150 feet
• 175 feet
• 200 feet
• 225 feet

Those distances provided a useful range for evaluating how the Tango followspots performed as the throw inc

Recording Equipment

We used a laptop to record the measurements as we took them.

Logging each reading immediately reduces the chance of confusion later. It gives the testing team a complete set of raw measurements to review before calculating the final published values.

Step 1: Prepare the Fixture

Before beginning the measurements, the followspot is prepared so the test reflects how the fixture is expected to perform in actual use.

For the Tango tests, we installed a new lamp and bench-focused the fixture before measurements began.

The beam was adjusted to produce a relatively flat field rather than intentionally creating a strong center peak.

This matters because concentrating as much light as possible in the middle of the beam could produce an impressive meter reading without accurately representing how the followspot would normally be focused during a performance.

Our goal is usable performance, not simply the largest number we can put on a specification sheet.

Step 2: Establish the Throw Distances

Once the fixture was prepared, we used the laser distance meter to establish exact measurement positions.

We placed tape marks at 100, 125, 150, 175, 200, and 225 feet.

Keeping those positions fixed allowed the same test to be repeated at multiple zoom settings without changing the distance between the fixture and meter.

This also makes it easier to compare how beam intensity changes as the throw lengthens.

Step 3: Test the Narrowest Zoom Setting

The Tango followspot was first adjusted to its narrowest beam angle.

For the Tango units tested, that setting was 4.5 degrees.

At each marked distance, we took three separate light readings and immediately entered them into the laptop.

Taking three measurements instead of one gives us a more reliable sample. If all three readings are close together, we can be more confident the measurement accurately represents the fixture’s performance at that distance.

If one reading differs significantly from the others, we have a reason to stop and investigate rather than publish the unusual number.

Step 4: Test the Widest Zoom Setting

After completing the narrow-angle measurements, we adjusted the fixture.