Solas (Gaelic for “light”) plays timeless music. The long-running Irish-American band, 15 years and counting, writes and performs warm Celtic tunes, often making social commentary in gentle tales of unsung heroes. These songs represent the soul of Irish music with acoustic instrumentation and poignant vocals, touching on immigrant experiences as well as the joys and heartaches of everyday folks. The group’s covers (Bruce Springsteen and Tom Waits) are as enticing as its originals. Leader Seamus Egan was inspired by his family’s history to create the concept for band’s current tour, “Shamrock City,” which tells the story of Butte, Mont., a turn-of-the-20th-century mining town where an Irish immigrant, Seamus’ great-great uncle, worked and died young.