"white" is subjective to humans.

LED displays, CRT displays, and LCD(flourescent tube lit/LED lit) displays all have variances in what it considers to be "white". Only when that variance is greater than what our eyes will compensate for, do we detect it as being "off".

The exactly output color for "white" depends on your hardware. Calibrating your camera to the white from an LED lit monitor/display will probably result in everything being recorded and displayed as "warm" since the LED white tends towards the blueish side. Same with flourescents, some LED bulbs, and your average hot shoe flash. They are all on the "cool" side.

White balance calibration of your camera is a "per environment + lighting condition" activity. What is "white" for a room lit with incandescent bulbs will not be "white" in another room lit by noon time sunlight.

Even with two monitors of the same model/build/make/etc. from the same store, will probably be off by a bit. You can calibrate the monitor to a white value or to one another, so that they are similar in white balance.

Basically:

• Your monitor needs to be calibrated (given your room, work environment, and lighting conditions)
• Your camera needs to be calibrated (given the environment, light situation, and your desired look)
• Your printer needs to be calibrated (for your given workflow, inks, paper, and intended display lighting situation )
• Your scanner needs to be calibrated (for that given scanner's sensor biases)

Sorry for the long winded answer. :) But in general, "white" on a monitor isn't actually white. Or rather, it is a particular color temperature range we generally call white.