Anno Lucis 

Abbreviated A.L.

Means the Year of Light. Or perhaps, as mentioned by Thomas Paine in "Origin of Free-Masonry" it may mean Year of the Lodge.

As used by Freemasonry it is calculated by adding 4000 to the normal A.D. dates.  The Masonic era is said to have begun in the Year of Light.  This would make sense because it would have been hard for any Masons to have been around before the Universe was created by God. 

Perhaps the early Masons adopted this date so that it would not be seen to be in conflict with the teachings of the Church that seemed to enjoy Burning at the Stake those who did not follow the official party line of the Church.

Most Masonic documents use both A.D. and A.L. for the year.

The 4000 is supposed to be the number of years before the birth of Jesus Christ that the world was created by the Supreme Being who is know to Christians as God.

The slightly more accepted time for the creation of the world is 4004 years before the birth of Jesus Christ as calculated by Archbishop Usher.  I doubt that he really had enough data to really do this calculation.

Does anyone still really believe that the Earth was made only 4004 years before the claimed birth of Jesus Christ?