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I would like to create a nice outside light for my interior scene, but without using hdri image (the rendering time increases a lot on my computer and most of all I can't find the way for correctly positioning the sun from hdri). What's the best solution? Should I use a jpg image or sky background and then positioning a sun light source?

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    $\begingroup$ Yes, the way you described in last sentence is correct. $\endgroup$ – Jaroslav Jerryno Novotny Nov 1 '15 at 17:47
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The problem with your question is that you are erroneously thinking that there are areas with lights and some without in a JPEG or other display referred image.

In reality, every single pixel is an emitter of light. As you may guess, with all of the crazy math involved in a ray tracing engine, all of that light ends up with a very complex interaction series in any image. This means that it is impossible to simulate real-world lighting without using some form of IBL.

Worse still, a JPEG is what is known as a display referred image. That is, the encoding of the image takes all of the data of a scene and maps it into the display referred range of 0.0 to 1.0. During this transition, you are losing a tremendous amount of the information in a scene.

The most ideal format for IBL is of course EXR[1]. This format permits storage of scene referred values from zero to infinity, which helps to encompass the complexity of most captured scenes.

[1] For those interested in the nerd stuff behind this statement, there is a great discussion of encoding quantization here.

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You can use portals to reduce your render time and get rid of noise in your scene while using HDR images. Here is a tutorial about using portals.

https://www.youtube.com/watch?v=oveSskhIEAc.

If you want to rotate the image you can use the following node setup enter image description here Otherwise the description in the last line will work fine.

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