The image below allows for examination and correction of a display's white point. It consists of six white regions. Each region contains one almost white digit. The numbers 1 through 6 represent the difference to pure white, quantified in so-called Lab luminance values. The Lab luminance L* (pronounced L-star) of the L*a*b* color system corresponds better to the differentiation behavior of the human eye than any other color system's luminance and far better than RGB values. This means that the same differences between L* values are also perceived as nearly the same differences by the human eye. Pure white corresponds to a Lab luminance of 100, so the figures' Lab luminance values are 99, 98, 97, 96, 95 and 94.
On a very good, correctly set up display you should even be able to distinguish the brightest figure 1 from the background. In any case you should see the figures of the lower row (4, 5 and 6). If only the 6 is distinguishable or no figure at all then your display's contrast is set up wrongly.
The white point is regulated by the contrast setting of your display (physical knob or screen menu). Change the contrast until all figures can be seen and the differences in brightness are close to even. Normally, you should not need to turn the contrast to maximum to achieve this.
People often recommend to set the contrast to maximum. But with modern displays this is generally not necessary. Besides, it shortens the monitor's life span and eliminates room for contrast increases that might be needed in the future (a CRT's contrast diminishes with time).
Please enlarge this window to fullscreen size and provide for dimmed ambient light without reflexes.
The calibration image presented here is a Lab image that was converted to sRGB. It was saved as a GIF file, therefore contains no color profile information. Your browser will only render the brightness differences correctly if your display's color space corresponds to sRGB and your system's gamma value is set to 2.2. This is the case with modern displays and Windows PCs even without color management.
For a more exact rendition of brightness differences download the calibration image as a TIFF file and open it with a color-aware application like Photoshop, preserving the color profile. In this case your system's gamma value is insignificant and the calibration image can also be used on Macintosh systems with gamma values set to 1.8.