With the youthful good looks of a dissolute poet, Syd Barrett was the poster boy for British psychedelia during the 1960s. Barrett named Pink Floyd, was the band’s lead singer/guitarist, and wrote most of its early material, including the first singles, Arnold Layne and See Emily Play, and all but one track on its debut album, The Piper at the Gates of Dawn. Released in August 1967, the album fused disorienting lyrics with guitar freak-outs and tagged the 21-year-old Barrett as a musical visionary. Yet, while Barrett died last Friday aged 60, his dream died three decades ago.

It has long been suspected that psychedelic drugs, perhaps in combination with some underlying psychological condition, dimmed and ultimately extinguished the radiant talents of Barrett, who became a cult figure as the lost genius behind Pink Floyd. Now, Barrett’s long-ago friend and former band-mate, David Gilmour, has advanced another theory: that the stroboscopic lights used to potentiate the effects of drugs at “London Underground” psychedelic music venues like the UFO, the Marquee Club and the Roundhouse contributed to Barrett’s breakdown.

Accounts of his collapse—the increasingly strange behaviour and unpredictability on stage—are legion. Biographers of the band revel in the stories, some apocryphal, some true. Like the time Barrett locked his girlfriend in a room and refused to let her out for three days, feeding her biscuits under the door. Or the concert at the Winterland, in San Francisco, where he opted to detune his guitar during Interstellar Overdrive until the strings fell off. Gilmour, a childhood friend from Cambridge, was invited to join Pink Floyd in 1968 to back up Barrett on guitar, but the founder’s deterioration continued and within months Gilmour replaced him in the band. After two haunting solo albums, The Madcap Laughs and Barrett, which show the last flickering light of his genius, Barrett was gone. He withdrew from public view entirely in 1974. He was 28 years old.

Barrett’s deterioration was initially attributed to “nervous exhaustion”—the consequences of the band’s sudden stardom, the stresses of touring, and especially drug use, on a fragile young artist. Others, however, postulated that a pre-existing condition, such as schizophrenia or Asperger syndrome, was to blame. Pink Floyd’s bassist Roger Waters said Barrett’s use of LSD compounded an existing condition, telling VH-1’s Legends in 2002: “There is no doubt those things are very bad for schizophrenics … and there is no doubt that Syd was a schizophrenic.”

But when I raised the issue in a recent interview, Gilmour produced an original theory for Barrett’s decline: “We did use stroboscopic lighting on stage a lot in the early years, and Pink Floyd before my time were warned about it, that you shouldn’t really do it so much. People did have fits and convulsions while the stroboscopic lights were going on. I certainly think the influence of the drugs they were on as well as the stroboscopic lighting could send anyone over the edge.”

Barrett, who turned 60 in January and who lived the life of a recluse in Cambridge, has continued to haunt Pink Floyd with his absence. He inspired the 1975 album Wish You Were Here (the song Shine On You Crazy Diamond is about Barrett), and actually materialized in the studio during the recording sessions for that album although his appearance had changed so much he initially went unrecognized by his former bandmates. He then slipped away and it was reportedly the last time any member of the band saw him. During the Live 8 reunion of Pink Floyd in July 2005, Waters said, “we’re doing this for everyone who’s not here, but particularly, of course, for Syd.”

As teenagers, in 1965, Gilmour and Barrett traveled to Paris where they bought Naked Lunch by William S. Burroughs, which had been banned in the United Kingdom. The two young men read it, Gilmour remembers, “by torchlight in a campsite near Paris, and we were terrified going through customs back into England, thinking we’d be arrested.”

Within months of that trip, Barrett was leading Pink Floyd into uncharted aural and visual landscapes. Melody Maker in August 1967 reported the band’s performances both “deafened and blinded.” Town magazine, writing about Pink Floyd as the “underground’s house orchestra,” described the light show: “projected slides bathed the musicians and audience in hypnotic and frenzied patterns of liquid-coloured lights. Honeycombs, galaxies and throbbing cells whirl around the group with accelerating abandon as the music develops.”

Scientific studies show that stroboscopic light at certain frequencies can stimulate illusory images—colour, pattern, and movement, even organized hallucinations—without the use of drugs. In a 1955 study, “A New Hallucinogen,” published in the Journal of Mental Science and based on clinical studies undertaken at the University of British Columbia, John Smythies became the first to report that flicker can also alter and enhance the effect of psychedelic drugs. For both reasons light shows became an integral part of the psychedelic underground in the Sixties, nearly as important as the music itself. As Barrett put it in a 1967 interview, “we think that the music and the lights are part of the same scene, one enhances and adds to the other.”

While most people exposed to flicker experience only beautiful imagery, a small number are photo-epileptics for whom it can induce a seizure, both mild “absence” seizures and the more serious grand mal variety. Some children with the condition have actually developed the habit of intentionally inducing the onset of absence seizures when exposed to bright light or strong sunshine by waving their fingers over their closed eyes. Researchers explain the behaviour as a way for the children to escape stressful situations or boredom.

Gilmour said the light affected his own playing: “It was pretty hard to play, on stage, absolutely straight. With that strobe lighting going on, even if you shut your eyes it made very little difference. It definitely does interact with the rhythms of your body or your brainwaves or something, it’s a pretty strange thing. It’s a great effect. It does take you to a place where you can feel that you’re having a certain amount of difficulty keeping your brain in the here and now. It’s quite good for a musicians’ brain not to be in the here and now, but to be sort of off in a world of its own.

“Syd’s demise, you know, has been blamed on the drugs, but it’s not out of the question to suggest that stroboscopic lighting allied with the drugs that he was on contributed to the collapse of his faculties.”

When informed of Gilmour’s theory, Smythies, now at the Center for Brain and Cognition, University of California, San Diego, responded this way: “It is certainly possible that chronic flicker and excess LSD could interact. I wonder if other rock stars have been similarly affected?”