IF IT'S POSSIBLE to photograph the human spirit, Valari Jack has done so. Outer strength and inner joy radiate from her portrait of a Colorado convent, now on display at Washington's Paul VI Institute for the Arts.

Jack, a freelance photojournalist, spent a year on this study of the Abbey of St. Walburga, in Boulder. She came away with a penetrating and engaging portfolio on the abbey's lively and devout nuns, who seem equally content while harvesting hay, attending mass or skateboarding.

No stuffy solemnity suppresses the joy of these energetic Benedictines, who are as likely to be found laughing together in the kitchen as lingering alone in the meditation grove. Jack, who lives across the road from the abbey, spent so much time with the nuns that they seem to have forgotten she was there. Or perhaps their lack of self-consciousness flows from the self-evident harmony of their lives.

Jack works with black-and-white film and available light. She's particularly adept with candlelight, as in one portrait that amounts to visual music: A rank of singing nuns, of various heights and each holding a taper that lights only her face and hood, forms notes on a scale. While the scenes are often dark, the faces of the nuns are invariably luminous, lit with inner light.

The exhibition is as balanced as the lives of the nuns, yet most of the photographs could easily stand alone as complete and self-explanatory vignettes: The sacrament of the mass and the sacrament of food preparation. A rosary draped over parchment hands, still as death. A rose delicately held in powerful young hands. Nuns in procession across the sere Western landscape.

Jack says her time with the nuns has changed her life; anyone who sees these pictures will know that without being told.