Diarmuid McSweeney, Rest in Peace: A Leader in Lighting and a Man of Integrity
Diarmuid McSweeney, past president of the Illuminating Engineering Society (IES) and a longtime leader at Holophane, passed away on February 26, 2025, just before midnight. He had been battling Cerebral Amyloid Angiopathy (CAA), a condition with symptoms resembling Alzheimer’s. He received compassionate care at a memory facility in Sarasota, Florida, where he enjoyed walking freely in its secure outdoor spaces.
His wife, Sydney McSweeney, shared that his love for lighting remained despite his illness. “A month before he died, I was reading an article from LD+A about the lighting of the St. Louis Arch. He was fascinated. Before that, I read him a piece about the lighting of the Acropolis, which we visited in 2018. The photography was breathtaking, and he enjoyed every detail.”
A Career Defined by Innovation
Born on May 13, 1940, in Dublin, Ireland, Diarmuid spent his early years sailing in Cork and later pursued physics at Trinity College Dublin. His academic mentor was Nobel laureate Professor Ernest Walton, and he served as captain of the college’s sailing and table tennis clubs.
Diarmuid started his lighting career at GEC in England before joining Holophane in Newark, Ohio, in 1968. For over 40 years, he held key roles, including Director of R&D, International Operations, Marketing, and the Lighting and Vision Center. He also earned a patent while working with Johns Manville Corporation.
Mark Roush, who worked under McSweeney at Holophane, recalls, “Diarmuid was my second boss, and the one word that comes to mind is fun! He was always serious, but always in a fun way. I remember him supporting my work as I carried three business cards for different roles Holophane assigned me. He was sharp as a tack and always on his game.”
Diarmuid was President of IES (1996-1997) and was honored as a Fellow (FIES). In 2006, he received the IES Louis B. Marks Award for his contributions to the lighting industry. He was also a vital force in the IES Progress Committee.
A Life of Service and Passion
Diarmuid was a devout Catholic and your humble editor often attended Mass with Diarmuid during the IES Annual Conference. In addition, Diarmuid was a dedicated Rotarian for 46 years, serving as President of the Granville, Ohio, Rotary Club and helping establish clubs in Pataskala and New Albany. He was also an avid sportsman, excelling in tennis, table tennis, platform tennis, and sailing.
Past IES President Mark Roush fondly remembers their office intercom system at Holophane: “I often tried to get Diarmuid to our application engineering office by announcing (in my best Irish accent), ‘Dire-Muud Mach-Sweeni to the Glen!’ He always arrived with a smile. So long, good friend and boss—RIP.”
Fred Oberkircher wrote to fellow IES Past Presidents, sharing a memory that best captured Diarmuid’s character. “After my first NCQLP Board meeting in Washington, DC, Diarmuid suggested we share a cab to the airport.” When the driver asked for their destination, Diarmuid surprised Fred with his response. He asked to go to the Vietnam Memorial.
Diarmuid requested that the driver wait while they walked the entire length of the memorial. He stopped several times to pay special attention to names marked by a note or flower. He never spoke about that visit, but it became their personal tribute at every NCQLP Board meeting that followed.
A Lasting Legacy
Diarmuid’s impact on the lighting industry and those who knew him was profound. His fun-loving spirit, sharp intellect, and dedication to excellence will not be forgotten.
His funeral Mass will be held on March 10 at Our Lady of the Angels Church in Lakewood Ranch, Florida, and visitation will be on March 9 at Toale Celebration of Life Center in Bradenton.
Sydney McSweeney summed it up best: “He was a man who loved light, and in many ways, he was a light—to his family, his colleagues, and the industry he cared for so deeply.”