Anno Lucis - (A.L. or A:.L:.) In The Year of Light
Anno Lucis is Latin for In The Year of Light.
Historical Significance: The Year of Light signifies the date of the creation of the world (approximately 4000 years before the Common Era), as we read in the third verse from the Book of Genesis in the King James version of the Bible as well as in the Torah.
1:1 - In the beginning, God created the heaven and the earth.
1:2 - And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
1:3 - And God said, Let there be light: and there
was light.
1:4 - And God saw the light, that it was good: and God divided the light from the darkness.

Ancient Craft Freemasons in the York and French Rites, residing in Scotland, England, Ireland, France, Germany, and in America, use the words, Anno Lucis. 
Math:  Anno Lucis is found by adding 4000 years (from the creation of the world to the present date) (4000 B.C.E. + 2021 C.E. = 6021 A.L. (Anno Lucis)
Relevance:  The Ancient Craft Mason Masonic calendar celebrates the creation of the world, approximately 4000 years before the Common Era, or 6021 years ago. (as of the year, 2021)  
The word, "approximately" must be used, here, because, historically, there were many different calendars in use over the last 6000+ years. 
This makes precise dates very difficult to ascertain.   (Some historians believe it to be 4004 years before the Common Era.)