It looks like you are using an image and a prop for the ground the character is sitting on but they each have different light levels. The background looks like it's much darker than the area she is in.
Is the background from an image (HDRI ?) that you set in the Render Settings Environment section? If it is I suggest trying to adjust the Environment Intensity and Environment Map sliders to bring more light into the background so it's closer to the foreground.
One quick thing I like to do is use an HDRI environment map to get nice looking realistic lighting and raise the light level so the background looks correct and the amount of light on what will be the shadow side of the figure is right. Keep in mind, this is for the shadow side.
Then I'll frequently add a light in the scene to brighten up the other side of the figure a little more. If I remember correctly I did that with this figure:
The background image is from the HDRI image and it's creating most of the light in the room. On the right side of the image I have a light making her left side a bit brighter, trying to create nice shadows on her.
What I've been learning about rendering is there's not a single "right" setting to use. There are a lot of variables and each image requires some adjustment to fit those settings.
Some important things to keep in mind are:
Iray prefers brighter scens, darker ones require longer renders usually.
When adjusting a light's "Luminous Flux" value don't be afraid of going very high - like 700K.
HDRI image maps can give you some great natural looking lights to the scene.
When I'm setting up a render I've started using these basic settings to start with in the Render Settings sections:
General: Set the image size.
Progressive Rendering: Everything at default then turn on Rendering Quality, set the quality to 3-5, then set the Rendering Converged Ratio to 99%. This so far has been a good starting point for me and then I'll adjust if needed.
Environment: I add the HDRI I like, rotate the dome to adjust how the light hits the character, and then set the Environment Intensity and Map values.
Tone Mapping: This is my last step usually. I'll adjust the ISO and/or Shutter speed to adjust overall brightness levels, set the Burn Highlights and Crush Blacks to .25 to start with, and sometimes I'll set Saturation to .25 if I think the image needs a bit of a kick.
Granted, these are just the starting point and every image will need some adjusting. As you use more HDRI maps you will see they vary in how much they light the scene. Some work perfectly and you may not even need to any any other lights for the image you want.
I'm sure I forgot a few thousand other settings but I hope that helps out. There are some good tutorials out there that helped me get a better understanding (thought I know I have a lot to learn still). I liked Iray Turbo by Dreamlight:
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