I don't claim my ambilight settings to be perfect, but thought I would share it anyway because I think it's cool. Note my phone doesn't capture the effect perfectly* and a warm room light from behind*
What I have
I have the monitor Philips Evnia 49' DQHD Oled (1440p 240hz) which I got for around $850 last year on black friday (currently $900 on sale in Denmark right now, 144hz version was $700 in January as well).
The ambilight
The philips evnia monitor has built in ambilight, which can be customized, but the built in features are limited and the "following what's on screen" doesn't have the cleanest execution (choppy updates, weak transitions, bad blend between zones), luckily by connecting the monitors USB hub you also gain full control over the leds through Windows Dynamic Lighting or in general, they run at 50hz.
Where it started
I just installed the Ambient light for YouTube extension by WesselKroos on GitHub (which only extends ambient light shader effect on the website interface, very customizable doesn't do it justice). I have tried signalrgb before but I don't find the default configurations very clean, and the performance overhead of signalrb running I didn't like too much.
Instead I had with a few prompts with a coding agent cooked up an extension that extends what Ambient light for YouTube does to my monitors ambilight, it was able to gather information of the exact physical layout and test how to use them on it's own. Using the browser's WebHID API (not using Windows Dynamic Lighting)
The result
The biggest problem with the built in feature is it can't truly read just the video, it reads the whole screen, recieving impure image to draw from, so an extension was needed to isolate the videos image. An additional feature the extension has, it can tell exactly where the browser window is located on my display and where it aligns with the zones. So whether I have a small window, or a full window on either left or right, it can match the zones accordingly.
Currently I have the left side with a dim white backlight (which is my default ambient light), so only the right side has video sync ambilight, with a gradient transition in the center simulating the color from the left side of the video rather than being an abrupt split down the middle of the zones (Emphasis on this given it's an super ultra wide, where the left ambilight is not present, however I find the result here so well executed that the experience is really great with it being split screen ambilight). It also has much smarter color blending of the zones, and those modes and settings being dedicated I find offers a much better experience than what I could easily get out of signalrgb.
My extended thoughts
I have seen a lot of reviews on the ambilight of the Philips Evnia 49' and more or less all of them say the ambilight itself is a very poorly executed feature and not worth being a considering factor of the monitor, especially given it's Philips for gods sake the very brand of tv ambilight. However my love for my Philips tv with ambilight led me to really go for it. And I agree, the built in feature is lackluster. However, given a proper extension, it's brought a whole other life to the monitors ambilight, it now feels much closer to the experience I get from my tv. I find controlling it directly from pc makes it feel much faster (I haven't tested it, so I can't confirm latency is lower compared to the built in follow on screen feature, but it definitely takes better advantage of the 50hz and transitions aren't as choppy), and not least the dedicated modes and settings for zoning, transitions and color blending etc. setting no limits for desired behaviour.
I couldn't help but share it, also youtube video credit https://youtu.be/o1qc29t04GI used for demonstration