I used a VrayCompTex as the dome's texture, which I used to composite HDRIs, and solve the dark problem which I mentioned before (Fig.45).
Next I needed to load an HDRI. There are two ways to load this: bitmap node and VrayHDRI node. The VrayHDRI node is easy to use and has good compatibility with V-Ray, but the bitmap node can adjust the image delicately. Usually I use the VrayHDRI node, but if the HDRI has a large dynamic range, I prefer to use the bitmap node to avoid bad blooming. As my sunset HDRI had a small dynamic range in 0.00-2.00, I used VrayHDRI here.
It's very easy to use a VrayHDRI node - just look at Fig.46. Then you need to set a suitable overallmult. The word "suitable" means that a white object will be white when it's rendered.
I paid attention to the VrayHDRI gamma. As a LWF standard, a HDRI's gamma should be 1.0, like the default setting. Because the HDRI is the original data of real brightness, it won't be corrected by gamma 2.2, like a JPEG file. But we can use a different gamma value to get a different HDRI performance. In laymen's terms, a gamma value of less than 1.0 makes an image darker and increases the contrast (in fact, it`s a sunken gamma curve). And a value of more than 1.0 makes an image lighter and decreases the contrast (so, it's a convex curve)(Fig.47).
I named the HDRI "Env_Main", rotating it to get a nice angle, which will decide the main light. When doing something like this, ActiveShade is your good friend (look at the top left corner window) (Fig.48).