# Lighting Question

Lightmap Resolution : Essentially allows for adjustment of the shadows across this surface. The lower the number, the tighter the shadows.

Use Two Sided Lighting : If true, this surface will receive light on both the positve and negative side of each polygon.

Shadow Indirect Only : If true, this surface will only create shadows from indirect lighting.

Diffuse Boost : Scales the amount of influnce diffuse color will have on indirect lighting.

Fully Occluded Samples Fraction : Fraction of samples along this surface that must be occluded before it is considered to be occluded from indirect lighting calculations.

I canâ€™t understand these things. Can you explain more easier?

Hey JinWooKim -

Lightmap Resolution - Lightmaps are essentially textures which are generated in the engine and overlayed on top of the scene to darken and lighten areas around which light hits. Because it is a texture that means it is dealing a pixel size. So the resolution is literally the size of that texture. (64, 128, 256, 512, 1024). The lower numbers in resolution create, relatively, bigger pixels so tighter shadows because the information is compacted into a smaller space.

Use Two-Sided Lighting - Normally polygons on meshes will only receive light calculations based on the positive side of the polygon (typically the interior of a mesh is not visible). This option exists to allow the calculation to be taken, a good example would be an open cylinder or cone.

Shadow Indirect Only - A Light in UE4 will generate information for direct light emission from the source itself and the indirect emission from bounces of the direct mission around the materials in the level. In this instance the object will only generate shadows from the indirect emission and not directly from light sources themselves.

Diffuse Boost - This is a multiplier for that indirect light emission discussed above. The indirect emission will take the color information off of the material it is bouncing and adjust as it casts itself on other objects. This boost will increase the influence the colors in the base color have on that casting.

Fully Occluded Samples Fraction - This actual controls the Ambient Occlusion that the object generates on other objects. Good pictorial example is on this page, under Ambient Occlusion.

Hopefully this helps you out -

Eric Ketchum