ROME – As a young man growing up in rural Bavaria in the 1930s, much about Joseph Ratzinger’s life revolved around the Church and its liturgical calendar. Born on Holy Saturday in 1927, he was especially sensitive to the use of light in the Holy Week rituals, above all the great Easter Mass.

Here’s how Ratzinger recalled the Easter service in the local church in Aschau am Inn, one of several small and medium-sized Bavarian towns where he spent his childhood:

“Throughout Holy Week black curtains had covered the windows of the church so that even during the day the whole space was filled by a mysterious darkness. When the pastor sang the words, ‘Christ is Risen!’, the curtains would suddenly fall, and the space would be flooded by radiant light. This was the most impressive portrayal of the Lord’s resurrection that I can conceive of.”

The interplay of light and darkness during the Easter season, so cherished by the young Ratzinger and generations of other Catholics across time and space, makes a two-day conference this week at Rome’s Jesuit-run Gregorian University on “Sweet is the Light: Light, Experience of God in History,” bringing together scientists, philosophers, poets, artists, theologians and others, especially timely in the run-up to the most sacred moments on the Christian calendar.

Jesuit Father Andrea Dall’Asta, director of the San Fedele Gallery in Milan and the holder of a doctorate in philosophical aesthetics, on Monday described the use of light in the works of artists such as Caravaggio – the acknowledged master of chiaroscuro, the interplay of light and dark – and Johannes Vermeer.

For instance, Dall’Asta said that in Caravaggio’s “Calling of St. Matthew,” completed around the year 1600, “Light is not just a rhetorical strategy, but it signifies a new spiritual and theological order. It points to a moment of choice, of refusal or obedience, a ‘yes’ or a ‘no.’”

In Vermeer’s “Girl with a Pearl Earring,” painted in 1665, Dall’Asta said, light is used to present “a simple scene of ordinary life caught in its extraordinary beauty and density, elevating it to the level of the absolute.”

In both cases, he argued, light is used to convey theological and spiritual meaning, well beyond its aesthetic effect.

Ironically, Dall’Asta came across as more confident in the artistic meaning of light than Jesuit Father Gabriele Gionti, an Italian astronomer who specializes in cosmology and quantum physics for the Vatican Observatory, seemed about how to explain light’s physical nature.

“To be honest, I’d prefer that someone explain it to me,” he said.

Gionti stepped through various historical phases in the evolution of the scientific understanding of light, arriving at what he called the “current model” deriving from quantum mechanics – that light is both, simultaneously, made up of particles and waves.

Along the way, Gionti noted that several major breakthroughs in the science of light came from Christian researchers, including the 19th century Italian Jesuit Father Angelo Specchi, considered the founder of modern astrophysics, and whose studies of the spectral qualities of light were driven in part by his fascination with eclipses and sunspots, which he examined from his perch at the Jesuit observatory at Rome’s Roman College.

Gionti said that while science today cannot fully account for the nature of light, what can be said is this: “Some physical phenomena can best be explained by assuming that light is constituted by waves, others by light being made up of particles, meaning photons.”

In other words, Gionti seemed to suggest, there’s still abundant space for mystery.

For Catholics, Easter is when the mystery and the power of light are most clearly on display, especially the Easter vigil Mass.

Today, the Roman Missal, the official collection and prayers and instructions for various forms of Catholic worship, describes it as the “mother of all vigils” and says it is the “greatest and most noble of all solemnities and it is to be unique in every single church.”

The quote, “mother of all vigils,” comes from St. Augustine’s Sermon 209.

According to the Church’s liturgical rules, the Easter Vigil must take place after dark on Holy Saturday. Holy water fonts in churches are drained, all the lights are turned out, and the tabernacle is supposed to be empty.

A section of the Easter vigil rite is called the “Service of Light,” dedicated to light as a symbol and manifestation of the resurrection of Christ.

It begins with the lighting of a fire outside and the inside lighting of the Paschal candle. The Easter candle is then processed through the church, with a deacon lifting the candle at three different times, singing, “The Light of Christ” (or Lumen Christi), and the congregation singing in reply, “Thanks be to God” (or Deo gratias).

Once that’s done, everyone lights their individual candle from the Easter candle, which continues until the whole church is alight. The idea is that the Paschal candle symbolizes the risen Christ, the “Light of the World.”

As the priest presiding at the Mass is instructed to say when the Easter candle is lit, “May the light of Christ, rising in glory, banish all darkness from our hearts and minds.”

So important is the role of light in the Easter vigil that there’s even a dispute among liturgists as to when, precisely, the lights in church should be turned on during the Mass – which tends to be a special preoccupation in First World settings, where on and off is a matter of flipping a switch.

According to the rubrics, or rules, which spell out how liturgies are to be celebrated, the lights in church should be turned on just before the Exsultet, a hymn of praise immediately prior to lighting the Easter candle.

Some liturgists, however, prefer to leave the church in darkness until the congregation sings the Gloria in Excelsis Deo, later in the Mass, on the grounds that it adds to the suspense and drama, and because it seems a more fitting moment. Others, however, insist that because the lighting of the candles belongs to the Service of Light while the Gloria is part of the Liturgy of the Word, it’s bad liturgical practice to confuse the two.

The mere fact there’s such a tussle illustrates anew the centrality of the interplay of darkness and light not only to the Easter vigil, but to the Catholic imagination writ large.

Never more than in the Easter vigil, in other words, is light designed to be for the Catholic eye what Dall’Asta said Monday it was for Vermeer in the 17th century.

“Light is not just an instrument that illuminates an obscure corner, but it’s a presence, it’s revelation, it’s an epiphany,” he said. “In it, every human being becomes noble, becomes a work of poetry, and small gestures become universal, transcendent, and eternal.”