When to choose D65 and when to choose ambient light temperature for white point for display calibration?

Question

In my case I am a programmer working with two monitor set up, mostly doing coding and occasionally viewing images. I do not print images, and I just want to pick a good white point for viewing code/websites/occasional on-screen images.

I have a room with a curtain where I get ambient indirect diffused sunlight (measured white point as x = 0.289 +/- 0.004, y = 0.339 +/- 0.002)

My goal is to match both monitors to the same white point and to enjoy color-calibrated displays for my work.

Namely in my case I want to pick a white point, but which one do I pick? Do I go with D65, or do I go with the measured ambient white point (i.e. values as above).

If the answer is "it depends", can you suggest other variables I need to consider.

I can also go with Native white point (which I estimate is around 8000K with a bit of a color-shift, something like x = .293, y = .294 when I measured it last)

My monitors are LED Acer S240HL

Note on custom RGB controls

During calibration I can choose to adjust my display's native RGB controls to match desired white point.

To achieve D65, I need to adjust monitor RGB controls to 99, 100, 85.

For ambient light in the room as white point I have to adjust RGB controls to 74, 100, 83.

For native I presume I can leave them all at 100. Does this tell you anything?

Trying out Native and D65

Since I have two monitors, I calibrated one with D65, and one with Native ... just to see some differences. Native looks more glaring and more contrasty, and whites are really white and stand out, while D65 looks more subdued, more matte more like you are viewing something on paper.

It does feel that Native white point brings out more of the display's color space.

I can make a case (for my monitors) that Native is better for development, since when looking at code more contrast helps, but I can also see a case for more subdued palette of D65 is easier on the eyes and more relaxing even if it is showing less contrast... Trying D65 for a bit before I will try something else.

Profiling Tools Used

i1Profiler software version 1.7.1 and X-Rite i1Display Pro calibration device.

Update:

Currently enjoying both monitors at "Photography" Display Setting, which is D65, 120 cd/m^2, gamma 2.2. Thankfully, both monitors calibrated to be incredibly close together to where color shades on one are pretty much the color shades on the other. And for whatever reason, calibrating with 118 default color patches worked better for me than with 462 color patches. 118 ended up not have a blueish or warmish color cast.

Answer 1

The majority of the monitors released in at least the last 5-7 years should have the native white point at 6500K, unless it's some specialized display, which usually cost much more. If the native white point of your display differs from D65, then there might be something enabled in the settings, like cinema or gaming mode. Before calibrating and profiling any monitor, always turn off all enhancements first!

Unless your goal is hard proofing a printed copy in an environment with calibrated light source, always calibrate your display to D65. In printing industry your light source and monitor would both be calibrated to D55 (5500K), so you could directly compare printed hard proof to the original displayed on the monitor.

Human eye itself is more or less calibrated to D65, that's why we perceive direct sunlight at noon, which is ~5500K as warm coloured. Our vision system registers the shifts in the colour of the lighting, but our brain psychologically adapts to the changes and we still refer to the light as white unless it's colour temperature drops as low as 3400-4000K. This psychological adaptation is what makes us remember this different degrees of warm white as simply white, same as 6500K.

Particular colour hues, on the other hand, are often remembered as we see them, disregarding the white point shift to some degree. That's why calibrating to D65 is essential for any colour critical work - so you would remember the colours correctly and your vision system won't have to adapt each time to different white point.

Answer 2

I don't see any mention of the use of a colorimeter or spectrophotometer, so at best, if you have perfect color vision yourself, you will only end up with "close enough" results via guesswork. Matching white point between devices is an extreme strain on the eyes. Use of profiling software and hardware would greatly ease this task.

Bear in mind that all you are doing is manually setting the white point. You aren't also making each step of grey neutral from black to white (a.k.a. "linearizing"). You aren't making as many other colors as close to perfect as possible. This is done by mapping differences between how your monitor is displaying a set of colors and what those colors should actually look like, and storing those differences in a color profile that your OS uses. You must use calibrating/profiling software and hardware to truly get as close as possible to accurate color display.

Bottom line/TLDR: If you need to see "good enough" color for web, I would go with D65. Most web users aren't color-managing their devices, and D65 is a good compromise for all the variations those devices will have.