Is the whiteness of a paper the same as its brightness?

No, these terms are not interchangeable. Brightness is the amount of light reflected back to the reader’s eye, while whiteness refers to the quality (rather than the amount) of light.

A bright sheet increases the contrast between the paper and the ink, which causes colors and photographs to “pop”. Grades of paper – premium, #1, #2, #3, #4 and #5 – differ from each other in the amount of brightness, with premium grade being the brightest. Bleaching paper increases brightness and moves paper up the brightness scale (with 100 being the brightest). Select a high-brightness sheet when your document has lots of photographs or lots of color.

A white sheet evenly reflects all colors of the visual spectrum (though papers inherently have either a warm, yellowish or cool, bluish hue). In general blue-white sheets appear brighter than yellow-white sheets (though this may change once ink or varnish is applied). If your document has a cool color palette (blues, greens, purples), a cool white sheet will make the colors appear brighter. If warm colors (reds, yellow, oranges) are dominant, they will appear clearer and more vibrant on a yellow-white sheet.