White Point for Prints
Things get more complicated when you involve print. Papers tend to have warmer white points much of the time, so the common default of 6500k makes white on a computer screen look quite a bit whiter than it does on print. Papers also come in an extremely wide variety, from very very warm (4800k or sometimes even warmer), to very bright, almost blue white (7500k or cooler.) This is where screen calibration is really important, as having your screen matched as closely to the papers you print on will make it easier to generate properly calibrated and color balanced prints.
When it comes to paper, the story is extremely complex. Paper is a very old enterprise that extends back over 600 years. There are some general buckets that you can put papers into, however: fine art paper, canvas, and coated/brightened. For me, and for many photographers, there is nothing quite like a good fine art paper. These papers come in a huge variety, from many material sources, including the common wood, but also uncommon sources like cotton, bamboo, and sometimes even mixed blends that may include animal fibers. The tones and textures of fine art papers are amazing, and can have a huge impact on the appearance and appeal of a final print. Fine art papers tend to be warmer, and its best to calibrate your display to a white point of 5000k. Canvas is another type of printable paper these days. There are also a variety of canvas papers, however much less variety than fine art papers. Canvas is also a warmer type of media, and can range from 5000k to 5500k. The third major bucket of paper includes coated papers. Many fine art papers are uncoated, non-brightened, letting the natural fibers produce the tone and texture of the paper. Coated papers cover the natural fiber base with one or more coatings to provide a smoother surface, surfaces that are more receptive and ideal for ink jet printing (or other types of printing), and protected from the elements allowing a longer-lasting print. Coated papers often also include optical brighteners to make the white point of the paper brighter and "whiter". Such papers often have much higher white points than natural papers, up to as high as 7500k or so. A white point of 7500k is extremely bright, bordering on blueish. Papers with optical brighteners are sometimes difficult to calibrate for, as the brighteners often depend on the type of light they are viewed with. Many brighteners use UV reactive components, and produce their brilliant white by reflecting UV rays from natural sunlight (or artificial gas lighting like flourescent tubes.) As such, their white point can change depending on the lighting.
