City inspectors say they believe the cause of eye irritation at a Northeast Philadelphia cheerleading competition earlier this month was ultraviolet light from a defective hall lamp.

More than 150 people who attended the event at Father Judge High School on Dec. 4 showed up at area hospitals complaining of eye problems.

The Archdiocese of Philadelphia closed the school while health officials made sure that there was no chemical or biological contamination in the school's gymnasium, where about 1,000 people attended the competition.

The school, on Solly Avenue in the city's Holmesburg section, reopened Dec. 8.

In a letter Wednesday to those who attended, a city health official said inspectors had found a defective metal halide lamp in the gym's ceiling.

The light exposed people to ultraviolet light, which apparently caused photokeratitis, wrote Dr. Steven Alles. Photokeratitis is painful but temporary.

Contact staff writer Robert Moran at 215-854-5983 or bmoran@phillynews.com.