The Sun doesn't seem to change according to the inverse square law when going from planet to planet.  4% of Earth's sunlight as Jupiter, 1% at Saturn, 0.25 % at Uranus and so on...just don't see a huge difference between them...Saturn doesn't seem to have 25% of the light that Jupiter does..I hope this can be remedied

Wow, this actually looks like some of the airless procedural worlds/moons in SE!  I guess SE did a pretty good job of indicating its surface brightness?  I wonder how the icy regions on Pluto look-- doesn't Pluto have a lot of ice on it-- even entire mountains made of ice?  I bet those would look absolutely spectacular!  And I wonder what the "heart" region of Pluto looks like from the ground?  And how large would Charon look since Pluto is basically a "double minor planet"? -- I still keep wanting to call it a planet lol.  And how much of a difference would be between day and night Pluto vs the night side of our Moon?

So if the Milky Way isn't visible on Pluto, can we say this is because of ground based light pollution?  In which case the sky should look brighter too because all that ground light is being reflected back up at the sky? So would a day or night on Pluto be more like a night in New York City or some other light polluted city? And how much of a difference would there be between a day on Pluto vs a night there?  Thanks!

NASA has a Pluto time website that shows how dark it is on Pluto at noon.

https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/plutotime/

Noon on Pluto is comparable to 15 minutes before the sunrise on Earth. The landscape is therefore quite dark.

I have paid 20EUR for Space Engine and have done test to perhaps help them. Or I am doing something wrong, in which case please correct me. All tests are with the sun at the same angle and placed in the corner of the screen.

Auto mode:

Moon: 


Pluto: 

(As you can see both are as bright as Sahara sand dunes in desert summer noon on Earth)


HDR mode (the non-realistic rendering mode):

Moon: 


Pluto: 
(Pluto is still way too bright)


Manual mode (our final chance for realism):
Setting a manual light level on the lunar surface comparable to Apollo lunar surface photography and seeing what the surface of Pluto looks like at this same level:

Moon: 


Pluto: 

And this is what Saturn looks like facing the sun at that same light level


Saturn: 


Obviously Space Engine is wildy inaccurate.
What can I do to make Space Engine look accurate, apart from guessing what the brightness should be by adjusting it manually myself?

Possible temporary workaround:
Seeing as HDR mode seems to be the most realistic for now, perhaps it is best to set a manual exposure that is comparable to HDR, perhaps a little darker

Go to Earth. Land in daylight.
Set exposure to manual so that it looks realistic.
Don't change the exposure.
Go to Pluto.
Notice it's pitch black.
Try to land on the daytime surface (while seeing nothing).
Notice the entire landscape is 0,0,0 RGB. I.e. pitch black.

Go to Earth. Land in daylight.
Set exposure to manual so that it looks realistic.
Don't change the exposure.
Go to Pluto.
Notice it's pitch black.
Try to land on the daytime surface (while seeing nothing).
Notice the entire landscape is 0,0,0 RGB. I.e. pitch black.

Very late reply here. But yes, this is correct, because a camera set to manual exposure would do the exact same thing, and that's what the manual exposure setting in SE is emulating. Set a DSLR camera to manual, and take a neutrally balanced exposure of a daytime landscape. Then with the same settings, take an exposure in typical bedroom lighting (around 100 lux to be same as Pluto). Your photo will be pitch black.

We found out earlier what your eyes would see, using a bit of math and personal experience with the closest analogue possible here on Earth. It's this moment about 30 seconds before or after the totality of a solar eclipse. The Sun is still blindingly bright and you can't safely look at it (you can't even tell that it's being mostly covered by the Moon -- that doesn't become obvious until the last few seconds.) Similarly, it would be unsafe to look directly at the Sun from Pluto, and it would even be difficult to tell that it's much smaller in the sky than as seen from Earth. Only the sharpness of shadows would clearly give that away. The ground around you will also still be fairly bright -- obviously dimmer than a clear sunny day on Earth, but still bright enough to see very clearly. It's not even into the realm of losing the sensitivity to colors (scotopic vision) yet.