L

Layer : A level of an image that can be edited independently from the rest of the image.

Lightness : The lightness (or brightness) of a color, independent of its hue and saturation.
Luminosity : The distribution of an image's light and dark values.
Line Drawing : An image created only from points connected by lines. It can be described using a series of end-point coordinate information. This can be combined with a weight which denotes the thickness of the connecting line.
Local Light Source : Light source that directly (i.e., not by reflection or transmission) illuminates a point on a surface.

Luminance : The absolute quantity of radiation emitted from a given light source or the brightness of a surface determined by the amount of light it emits or reflects.
Luminosity : The relative quantity of radiation emitted by a light source.
LUV Space : A color space similar to the XYZ model, except that the components are scaled to be perceptually linear. The human eye perceives brightness on a logarithmic scale, and hence LUV components are logs of the corresponding XYZ values.