Any monitor and calibration package that supports DDC (automated control over the monitor settings via software) allows you to hide either the monitor or yourself under a blanket.
There are three primary ISO specs that cover print viewing and display luminance. ISO 3664:2009 specifies the conditions for evaluating a print or an image on-screen, but not necessarily both at once. ISO 12646 lists requirements for comparing soft and hard copies, while ISO TC130 (included in ISO 12646) describes soft-proofing procedures. The quick summary along with some editorial comments:
Print viewing (ISO 3664):
- Critical comparison (P1 appraisal level): 2000 lux. This is definitely not for soft-proofing, as the illumination corresponds to a monitor luminance level of 570cd/m2. The reason the light is so bright is to maximize shadow resolution. Recent research shows that illuminance levels above 600 lux reduce the ability to perceive color differences in saturated colors except for yellow, so this number may well change in the future.
- Practical comparison (P2 appraisal level): 500 lux. This viewing condition corresponds to a monitor white luminance of 160 cd/m2, so there is some hope of accurate comparisons. Shadow details may appear compressed vs. the P1 level, but color variances are at least as visible.
- S Appraisal level (soft proofing only on a monitor): At least 80 cd/m2 with a D65 whitepoint and ambient light at or below 32 lux. The assumption is that one is editing for the web.
Soft proofing (ISO 12646 with TC130 procedures):
- Soft-proof only: D50 display whitepoint, minimum 80 cd/m2 luminance, maximum ambient light of 20 lux.
- Soft-proof with comparison to hard copy in a viewing booth: Hard copy illuminanted at P2 appraisal level, display at least 100 cd/m2, with 160 recommended, display whitepoint matches viewing light color temperature, maximum ambient light of 20 lux.
- Soft proof with the display integrated into the viewing booth: As above, but max of 64 lux around display.
What does this heap o' numbers tell us? First. the ambient light level is seriously low. 20 lux approximates a fireworks display. 8 seconds at f/8 for 100 ISO. There are multiple reasons for this cave-like value. The first is that the display whitepoint is set to D50. For most people, this reads visually with a yellowish tint unless the display luminance is very high and the ambient lighting low. The second is that the only consideration is maximum correlation between screen and print. Darker ambients work better. The specs also still hark back to the CRT luminance levels of 80cd/m2. Finally, these specs are geared toward typical commercial printing on groundwood stocks, which have a more yellow base than most artsy inkjet or photo lab papers. Moving the display whitepoint to the D60-D65 range helps here.
In a more realistic work environment, one where you need to see keyboard, mouse, and tablet, increasing the ambient light will not make much of a difference in the quality of comparison. Matching the viewing booth illumination level to the display is, however, a good idea. Higher quality booths support the 500 lux/P2 illumination level, or a display luminance of 160 cd/m2. Depending on how dark a room you wish to work in, and whether your viewer has a dimmer, lowering the display output is certainly possible.