Why did St. John Paul II add the Luminous Mysteries to the Rosary? I started praying the Rosary after St. John Paul II added the Luminous mysteries to the Rosary, so I virtually no remembrance of a Rosary being prayed before they came on board.  When he writes about them in Rosarium Virginus Mariae he kind of just slides them in and says what he thinks they should be.


  Moving on from the infancy and the hidden life in Nazareth to the public life of Jesus, our contemplation brings us to those mysteries which may be called in a special way “mysteries of light”. Certainly the whole mystery of Christ is a mystery of light. He is the “light of the world” (Jn 8:12). Yet this truth emerges in a special way during the years of his public life, when he proclaims the Gospel of the Kingdom. In proposing to the Christian community five significant moments – “luminous” mysteries – during this phase of Christ's life, I think that the following can be fittingly singled out: (1) his Baptism in the Jordan, (2) his self-manifestation at the wedding of Cana, (3) his proclamation of the Kingdom of God, with his call to conversion, (4) his Transfiguration, and finally, (5) his institution of the Eucharist, as the sacramental expression of the Paschal Mystery. 


So, does anyone know what prompted him to add more mysteries?  He explains why he chooses the individual mysteries in the letter, but he doesn't really say why he thinks that the Rosary needed more stuff.
No one knows for sure where Pope St John Paul II the Great got the inspiration to add the Luminous Mysteries to the Rosary.
The history of the Rosary shows a wide variety of styles, due to the unique inspirations of an individual or even a Religious Order. St John Eudes (1601-1680) is a good example of employing different ways of using a rosary in one's life of prayer in his treatise on The Life and the Kingdom of JESUS.
It is obvious that Pope John Paul II desired to make the traditional mysteries of the Rosary to be expanded to include Jesus' public life and more Christological.

I believe, however, that to bring out fully the Christological depth of the Rosary it would be suitable to make an addition to the traditional pattern which, while left to the freedom of individuals and communities, could broaden it to include the mysteries of Christ's public ministry between his Baptism and his Passion. - ROSARIUM VIRGINIS MARIAE

The probable origins of the Mysteries of Light and Pope John Pal II's inspiration for them came from Saint George Preca (1880-1962). He was canonized by Pope Benedict XVI on June 3, 2007.

It is not yet known whether these new mysteries were actually taken from those proposed by Dun Gorg (as the new Blessed is affectionately known in Malta). But it is certainly a curious fact that, apart from some small differences, the five mysteries are identical to those proposed by Fr Preca. Interesting as well is the fact that the Pope has called these mysteries from Christ's public life “the Mysteries of Light”, the same title given originally by Fr Preca when he first proposed them in 1957. - Probable Origin of the Mysteries of Light

Fr. Dolindo Ruotolo may have been  Fr. Preca’s inspiration!

The Misteries of Light were proposed and included in the Rosary by Pope John Paul II with the Apostolic Letter of October 10, 2002
The Mysteries of Light are taken from the Commentary on the Gospel of St. Luke and St. John written by Father Dolindo Ruotolo (1939).


The Sacred Scripture: The Gospel According to Luke (Don Dolindo Ruotolo) Book 1