Difference between D L Sugars

D and L are optical isomer of each other, or non superimposible mirror images. The convention uses Glyceraldhyde as the reference. In a fisher projection the OH of glyceraldehyde is on the right side ( more improtantly in the R configuration)in the D isomer and on the left side ( or the molecule is in the L configuration) in the L isomer. So for all other sugars it looks at the last chiral center for the molecule if the chiral center is R it is a D isomer if the last chiral center is in the S configuration it is an L isomer.