Back in 1975 I was in my final year of engineering school, preparing for what I assumed would be a long and fruitful career solving problems and designing new ones. Meanwhile I was spending most of my free time honing my skills as an aspiring journalist with the college’s weekly newspaper. Truth be told, I spent a lot more time in the newspaper’s office than I did in the physics or chemistry labs, which should have given me a clue about my future, but what did I know at that age?

Led Zeppelin was arguably the biggest rock band in the world back then and when they announced their U.S. tour, every venue sold out in a matter of minutes. So, figuring I had nothing to lose, I called up their record company and somehow managed to talk my way into a pair of free press tickets to their show at New York’s Nassau Coliseum. Never having covered a concert before, I knew nothing about backstage passes or the photographer’s pit at the foot of the stage, so row 18 on the floor in front of the stage sounded okay to me.

Considering how little I really knew about photography at that point – I’d only been using a 35mm camera for a couple of years – I didn’t do too badly. In fact, I got downright lucky with one shot. It was midway through the song “Dazed and Confused,” and I know that because you can see Jimmy Page using a cello bow on his Gibson Les Paul guitar. It was a trick he used to great effect in concert. John Bonham’s drum kit is glowing as if it’s on fire, and Robert Plant is striking one of his patented rock god poses. But what makes the shot so unique is that off to the left, behind the drum kit, you can see three laser beams piercing the clouds of colored smoke.

Today lasers are a common theatrical tool, but back then they were a rare phenomenon. So much so that I recently wondered, was Led Zeppelin the first rock group to incorporate a laser in their stage shows? Apparently that’s been a matter of debate for years. Some people think The Who were first when they spectacularly introduced a Spectra-Physics 164 argon laser into their show at Granby Halls in Leicestershire, England on October 18, 1975, but the Led Zeppelin photo was taken on February 13, 1975, so it’s quite possible they were the first group to use one on tour.

With my curiosity piqued, the question then became, whose laser was it? Given what I’d learned about The Who’s set-up, Spectra-Physics were the obvious suspects, so I contacted my friends Marlene Moore and Patti Smith of Smith Miller Moore, the ad agency that does PR work for Spectra-Physics, and asked if they could do some digging for me. Unfortunately a lot of water has passed under the bridge in 37 years, and although the folks at Spectra-Physics thought it was highly likely that it was one of their units, they couldn’t be certain. The mystery deepened when Moore showed the picture to another laser expert, Dr. Austin Richards of FLIR, who thought it looked like an early krypton laser.

My search for the truth finally paid off when I tracked down a gentleman named Jack Calmes, who heads up an architectural and theatrical lighting company called Syncrolite in Dallas, TX. In the 70s Calmes was one of the founders of a company called Showco that did sound and lighting for most of the major rock acts of that era, including Led Zeppelin and The Who. I figured if anybody would know, he would, so I e-mailed him a copy of the picture and asked if he remembered whose laser Led Zeppelin used on that tour. A few hours later I had my answer.

“Our first laser with Led Zeppelin was a 500mW Coherent radiation krypton laser,” said Calmes. “Not sure exactly when that was – perhaps in 1974/75. It is very possible that your picture was our early krypton. It was one unit behind the drum riser. Thereafter we bought only Spectra-Physics lasers, and I also sold some to The Who as well. By the end of the 70s we had the fiber optic bow and pyramid scan over Jimmy Page for Dazed and Confused.”

So there you have it. Thank you, Mr. Calmes, for solving a mystery that was 37 years in the making.

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