1. To add color, light, or cheer to a space (perhaps one that is dim, dark, or gloomy). I can't wait for the flowers I planted to blossom into beautiful colors and brighten up our yard. A new paint color really brightened up that old house.
2. To make something lighter in color. I'm thinking of brightening up my hair with some blonde highlights. It really looks like rain right now—I'd wait to go out until the sky brightens up a bit.
3. To become happier in mood, especially after one has been glum or sad. Your mother really brightened up when she got the flowers you sent.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
to become brighter; to lighten, especially with sunshine. The sky is brightening up a little. When the morning sky brightens up just a little, the birds begin to sing.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
1. To become brighter or more intense in color: The sky brightened up quickly as the clouds dispersed.
2. To make something brighter or more intense in color: Some red paint will brighten up this dreary room. Put some yellow into the dye to brighten it up.
3. To become happier; improve one's mood or outlook: He brightened up after you began talking with him.
4. To make someone happier or more cheerful: The sunny weather brightened up the tired travelers. A cool glass of lemonade would brighten me up right now.
The American Heritage® Dictionary of Phrasal Verbs. Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.