I've read a few concerns over the PS5 running in HDR mode all the time, so I decided to do some testing (disclaimer: I'm no expert).
Using a i1Display Pro and the iProfiler software, I've been able to measure the peak brightness of the PS5 in HDR and SDR on the LG CX OLED using the display uniformity test.
I've annotated a screenshot of the results here:
It should be self explanatory, if not heres the breakdown...
Four measurements have been taken of the PS5 UI, all measuring a white patch on screen for the Luminance (brightness). One was on the Adjust HDR screen in settings and the other three are using a game logo in the library with a white background, similar to the 10% window on screen 1/3 in Adjust HDR.
HDR On, Peak Luminance of the White Game Logo:
So firstly, using my calibrated picture mode "Game (in HDR)", I measured about 243cd/m2. Noting that this isn't the maximum brightness that the screen can achieve.
HDR Off (SDR), Peak Luminance of the White Game Logo:
Using my calibrated picture mode "Game (in SDR)", I mesured 97cd/m2 which tallies up with the reference brightness of 100cd/m2 for SDR content in a dark room.
HDR Off (SDR), Peak Luminance of the White Game Logo:
I then changed to the "isf Expert (Bright Room)" picture mode and I measured 215cd/m2, which is close to the brightness measured with HDR on.
Adjust HDR Screen Peak White (2\3):
Finally for verification, I measured about 636cd/m2 in "Game (in HDR)" picture mode, which is approximately the brightest white any pixel on my TV will go. Meaning that the other HDR result wasn't being clipped by my calibration.
Note: I missed it off on the image above, but the measurement on the Adjust HDR screen 1/3 for the full field white was 128cd/m2.
I think if anyone is concerned about getting burn-in from the PS5 UI elements in HDR mode, it looks like Sony has set the peak brightness of anything on screen in the UI to be approximately the same as SDR when using a picture mode meant for bright sun/daytime viewing e.g 215cd/m2.
This all means that, running in SDR to prevent burn in of the PS5 UI on an OLED TV is probably not worth it.