Now former students and colleagues are determined to see that light shine on.
Shortly after Mal died in February, some Penncrest High School alumni started Mal's Memorial Fund. The goal: to raise $50,000 to create an endowed scholarship in Mal's name so that every year, one boy and one girl from the Media school would get $1,000 to pursue an interest in science.
The drive has had amazing success. With just $3,000 more to go to meet the endowment requirements, the fund's organizers will be able to give out the first scholarships to this year's seniors.
"We want to strike while the iron is hot and keep his legacy alive," said Bill Kane, 33, Penncrest Class of 1997.
As he did for many students, Mal had a big impact on Kane's life.
"I pursued a career in engineering," he said. "Part of the reason was my experience in Mr. Mal's class."
Mal also left a mark on Jonathan Miniman, another of the Class of '97 who also helped create the fund.
"I can still see his face, hear his laugh. He was larger than life," Miniman said.
Now a finance executive - a career decision Mal helped him make - Miniman, 33, figures he clocked hundreds of hours working on Penncrest's Physics Olympics team, which Mal helped coach. "We all wanted to win for him."
Mal, he said, was the first educator who taught him to think analytically. But he did even more.
"At the very highest level," Miniman said, "he taught you to be a good person."
Mal was many things to many people. An artist, he made intricate model soldiers and kept his students' attention with blackboard cartooning. A lover of flight, he launched rockets with his students. An avid outdoorsman, he wore his hunting jacket and a big smile while directing traffic in the Penncrest parking lot.
But above all, Mal loved his students. He logged 40 years as a teacher, first at Ridley High School, then at Radnor, and, since 1989, at Penncrest, in the high-performing Rose Tree Media School District. A brief marriage ended in divorce, and Mal had no children. But "he had hundreds of kids," said his youngest sister, Betsy Juhasz, 54.
Even when he was at his sickest, they were on his mind, she said. "He said, 'If I go down, I'm going to go down swinging. I want my kids to be proud of me.' "
To Jim Ciccarelli, 45, a fellow physics teacher at Penncrest, Mal was a mentor and friend. They met when Ciccarelli, then an engineer, went back to school at age 27 to go into education. He had to observe a teacher in action, and a friend who was a Penncrest graduate told him to look up Mal.
During the observation, Mal, who regularly gave students his home phone number, told them he would be away that weekend and hard to reach. He suggested they ask Ciccarelli for his number, and he complied.
Not long after, the younger man asked Mal whether he could be his student teacher; Mal never had accepted a student teacher.
"He said, 'I'm going to make an exception because you gave them your phone number,' " Ciccarelli recalled.
And the students loved Mal's company, hanging out in his classroom, a busy, happily untidy place where Mal played the vintage country-flavored rock he loved - the Grateful Dead, the Allman Brothers. The kids even got to like it.
Mal also tried to draw girls into science, to build their confidence.
On Feb. 12, Mal didn't show up for the job that was his life's passion.
The night before, he had texted his two sisters with the good news: the cancer was gone. "Life is looking better," he wrote Juhasz. He was talking excitedly about plans for the future.
But when he didn't show up the next morning, Ciccarelli had a mutual friend look in on him at home.
He was found sitting at his desk, a glass of wine nearby, a cigar in hand, his music playing.
In the weeks since, Mal's siblings say, they have been greatly touched by the testimonials.
And what would he make of a scholarship in his honor?
He'd probably be moved to tears, Juhasz said.
"If he knew about it, it would have been the most important thing he contributed," she said, "because he was all about the kids."
For more information about the fund, go to: http://www.malsmemorialfund.com
Contact Rita Giordano at 610-313-8232, firstname.lastname@example.org, or follow on Twitter @ritagiordano.