This is an answer based on your additional question in he comments: "You mean that if I add an HDRI to World Environment Texture with strength 1.0, it doesn't resemble real world conditions?"
No, not really. Because "real world conditions" in photographs or even your eyes are always in some way or another adjusted. Your eyes adjust automatically by changing the size of the pupil. Photos taken are always depending on aperture and exposure time. No camera can picture the whole dynamic range of the world, so HDRIs depend on how they were created and by whom and can vary in brightness as well, even if you set them all to a strength of 1.
Here is a comparison - all three HDRIs are from Poly Haven, all are taken with clear skies at noon (as you might see in the reflection on the left sphere), all are rendered with the world's Strength at 1. The first one on the left is the brightest and seems a bit overexposed, the middle looks "normal", but the right one is very bad and dark - even though when you look at the original image, everything there is in bright sunlight and objects there have clear shadows. But the scene looks so dark as if it was just a JPG.
"Real world conditions" for a clear blue sky have the sun at a power of about 1000 to 1360 W/m², which is the unit of the Strength in Blender sun lamp object. The blue sky in the shade has a power of around 1/6 of the sunlight, so roundabout 1000/6 $\approx$ 167 W/m² to 1360/6 $\approx$ 227 W/m².
Easy, isn't it? So take a sun lamp, set the Strength to 1000, give the world a blue color and set it to something like 160 and there you go.
The settings:
The result:
Okay, not so good - maybe a "bit" overexposed? Now, why is that? Because Blender's camera is not a real camera. Sure, you can change the Exposure in two different places (apart from the Compositor), in the Color Management settings or under Film > Exposure - but what you cannot do is change the aperture or exposure time to let more or less light fall onto the sensor (which the camera also does not have of course). There are Aperture settings in the Camera Properties, but they are used to simulate depth of field.
Anyway, as I said what you can do in Blender is change the Exposure in the Color Management with a default value of 0 or under Film, there the default is 1.
The difference is as follows: Color Management uses "stops" as unit, which comes from photography. Exposure = 0 means average brightness, the camera changes aperture and time so that the average brightness of the image is 50% grey (camera sensors only work in greyscale, simply spoken). Each stop plus means the brightness gets doubled, each stop minus means the brightness gets divided in half.
The Film > Exposure setting is a scale factor. 1 means 100% the brightness as it is, 0.1 means 10% of the brightness. 0 means, the image is absolutely black - yes, even emissive objects etc., it is the equivalent of the camera shutter being completely closed.
Another important difference between Color Management and Film: Color Management ist a post-process and you can change the brightness of the image after rendering, while Film is affecting the render itself. Rendering something dark with an Exposure of 0.1 cannot be brightened up by setting the value back to 1, it will stay dark.
Now here is the scene with the very bright sun and sky again. On the left is the image as it was before, but the Color Management > Exposure set down to -7 (stops). -7 stops means, the image brightness is only $(\frac{1}{2})^7 = \frac{1}{128}$ of the original brightness.
On the right is a new render of the image, the Color Management > Exposure at the default 0, but the Film > Exposure set to a factor of $\frac{1}{128} = 0.0078125$ and as you can see, the results are the same.
But taking photographs with a real camera usually does not require to set such extreme negative exposure values - because as I mentioned earlier, real cameras control the brightness of an image through aperture and exposure time. Changing the exposure value to something higher or lower is only used to deliberately force the camera to over- or underexpose from the standard medium brightness.
But since Blender's camera does not have the functionality to let more or less light in, you have to manually adjust the Strength value to your liking. This usually is no problem for only indoor or outdoor scenes, however if you want some auto-exposure effects in an animation when moving from dark environments to bright environments and vice versa, then you have to use tricks like animating exposure values or the strength of light sources.
But notice that when you for example animate the Strength of the world and decrease it to simulate a lower exposure you have to be aware that when you have other lamps in the scene (like the ones inside the tunnel) will suddenly appear much brighter compared to the sky if they do not decrease in Strength as well, since a camera cannot expose the lamps and sky differently within the same photograph. So for these effects it is always better to animate the overall exposure than separate light sources.
