Difference between Lighten and Lighten Up

LIGHTEN vs LIGHTEN UP: VERB

To descend; to light.
To burst forth or dart, as lightning; to shine with, or like, lightning; to display a flash or flashes of lightning; to flash.
To grow lighter; to become less dark or lowering; to brighten; to clear, as the sky.

To free from trouble and fill with joy.
To make light or clear; to light; to illuminate
To illuminate with knowledge; to enlighten.
To emit or disclose in, or as in, lightning; to flash out, like lightning.
To make less burdensome or afflictive; to alleviate.
To cheer; to exhilarate.
To make lighter, or less heavy; to reduce in weight; to relieve of part of a load or burden

To make lighter in color or shade: as, to lighten the background of a picture.
To cheer; gladden.
To make less burdensome or oppressive; alleviate: as, to lighten the cares of life.
To make light or less heavy; reduce in weight; relieve of weight: as, to lighten coin by clipping or abrasion; to lighten a load or a ship.
To become light or less heavy.
To send forth like lightning.
Make more cheerful through the use of color
Reduce the weight on
Make lighter
To illuminate mentally or spiritually; enlighten.
To make light or bright; give light to; light up.
To emit flashes of lightning; shoot out as lightning; flash. See lightning. The lightning that lighteneth out of the one part under heaven shineth unto the other part.
To become light or lighter; grow light or clear up; brighten: as, the sky lightens.
To descend; settle down; light.

Enlighten, Minimize, Ameliorate, Simplify, Relax, Alleviate, Ease, Reduce, Relieve, Soften, Lessen, Loosen, Buoy up, Lighten up, Brighten

Streamline, Diminish, Enlighten, Minimize, Ameliorate, Simplify, Relax, Ease, Reduce, Relieve, Soften, Lessen, Loosen, Buoy up, Brighten

Christmas cheer that helped lighten up the screen.
Do this daily till the dark circles lighten.
How about a poem to lighten things up?
Can You Lighten Up Corned Beef and Cabbage?
Lighten the mood with a funny Christmas card.
Lighten up and learn to compromise on occasion.
Acetone will cause the colours to lighten considerably.
Take a look and feel your shoulders lighten.
Messiah will lighten the righteous when he comes.
But things lighten up, as much as they can ever lighten up in the ACC, over the next three weeks.

Lighten up and introduce yourself to these little travelers.
But he was in no mood to lighten up.
Lighten up and learn to compromise on occasion.
Dude, lighten up and embrace the free publicity!
Christmas cheer that helped lighten up the screen.
Can You Lighten Up Corned Beef and Cabbage?
We must stand up against these word police and say enough is enough, lighten up people.
QUESTION so everyone should lighten up and tell me about those people up north.
Language Developing a clear style Tighten up, lighten up.
But things lighten up, as much as they can ever lighten up in the ACC, over the next three weeks.