You're missing the point. Of course the nits don't change, but your perception does as others have pointed out as well. For some, 300 nits is very bright, for some it's dim. Make a simple experiment, take a reference display, let someone else calibrate to 6500K and set the brightness to specific nit value. Then you can enter the room and look at the display. I seriously doubt you will be able to tell how many nits the display is set to just by looking at it.
No, no and no. I used to develop system solutions for image representation and you can bet that rarely does a display spec live up to the real world performance. What is the 300/400/500 nits based on? Peak brightness? Average? Something else? At what color temperature where these readings taken? What black level? What patterns were used?
Display manufacturers will almost certainly make these measurements with color temperature way off, because brightness will be higher. For a real world application, you want color temperature closer to neutral, which mean's it dimmer. Still, the display can deliver the brightness, just with colours way off. If you want to take all variables out of the equation, you have to specify all parameters, which no manufacturer does. No one will go through the hassle of doing this, especially on a cheap display such as one from a MBA, MBP, iMac or whatever. The reference displays I used in the past were between $10k to $50k for a single display in the range of 20" to 27". And this is not a problem with measurements, I think I used fairly good equipment from Photoresearch and Konica Minolta ($10k to $20k) and in special cases NIST certified equipment ($-six-figure range). I think the equipment was accurate enough to take reliable measures. That's why you always buy more brightness than you actually need, because the end result will always show less. That's a well known fact in the industry. Look at any calibration report for any given display.
It's the way it is, from every manufacturer. Name a single display device that lives up to the brightness spec. Why don't you go out, buy a Sony VW5000ES, which is an excellent device (at $65k it should be!), calibrate it and report back how much of those 5000 lumens in the spec sheet are left. It's not just brightness, it's CR measurements as well, among others. These are made under conditions you will never have in the real world. And if you think this in an exception, you're in for a surprise. Again, get the proper equipment to measure and start doing it. You won't like the results.
What makes you think that? Apple doesn't have to provide anything. They can, but they don't have to. If you don't like that, don't buy it. And besides, they're specifying the MBA as 300 nits. They do not specify under what conditions and they don't have to, no manufacturer does. Everyone knows this is marketing and the real numbers are lower.
If you need more specific numbers, ask the display manufacturer to provide them including parameters for the conditions these measurements were made (Apple probably doesn't know, because they just buy the displays). If you need specific numbers for your MBA, buy the proper equipment and measure. Or let a calibrator do it for you. Those that have at least basic knowledge are most likely listed at the Imaging Science Foundation.
