It is possible to rotate the background image you attach to the Material Room Backgrond node.

The way to rotate the image is to use a Mapping Node. Click on the value of the Rotation option. You will see 0,0,0 representing rotation axes x,y,and z respectively. Leave the x and z as zero. Change the Y value to anywhere between -1.5 to +1.5 to get your preferred lighting (and background, if you don't use any additional background). These values are in Radians, not Decimals. You can preview the dialled result if you have the Auxillary Viewport open and set to auto-refresh (I prefer to render in SuperFly).

Here is my set-up. I have added HSV and Gamma control nodes so that I can adjust the quality of the illumination coming from the node into my scene. I do not need any Poser lights. All the illumination comes from this setup.

Additional tip:

I have an old hardware rig - an nVidia GTX 1080 GPU. I don't need to render at extremely high resolution for very long render times. I use a lower render setting to save some time, then use the Intel denoiser, which is an Artifical Intelligence trained to improve images.

Here are my renders using my setting for Background Node as shown above.

This is the Intel Denoised version:

This is the original fast render:

All light comes only from the background node with my 360 equirectangular image plugged in as shown.

Erratum - in my opening post, should read "Radians, not Degrees. Apologies."

It is possible that you do not need the HSV and Gamma nodes if you have a good quality HDRI image. But you will need the Mapping node if you want to rotate the image in the shader tree.

If that interests you, you will find here the source of a small Python script I've written to ease the setting of the Y value

Y-Phil posted at 7:33AM Thu, 06 May 2021 - #4418543

If that interests you, you will find here the source of a small Python script I've written to ease the setting of the Y value

@Y-Phil - Thanks for adding the comment - others browsing this thread will also be able to refer to your script.

infinity10 posted at 7:41AM Thu, 06 May 2021 - #4418546

Y-Phil posted at 7:33AM Thu, 06 May 2021 - #4418543

If that interests you, you will find here the source of a small Python script I've written to ease the setting of the Y value

@Y-Phil - Thanks for adding the comment - others browsing this thread will also be able to refer to your script.

You're welcome ?

You can use the HSV node to change the light tint by cycling through the Hue value.