What is Light Samples Multiplier - LSM?


Number of direct lighting samples per each GI sample.


Increase this value in scenes with visible noise in direct lighting. Default value of 2.0 works well in most cases.



You can find "Light Samples Multiplier" parameter in Render setup > Performance > Performance Settings. As its name suggests, it multiplies the amount of samples specified in "GI vs. AA balance" by a given factor to use them for direct light sampling. Total amount of samples is dependent on "Light Samples Multiplier" and "GI vs. AA balance" values. If "Light Samples Multiplier" is set to 1 and "GI vs. AA balance" is set to 16, this means that 16 GI samples and 16 direct light samples will be used for each pixel per pass. If "Light Samples Multiplier" is set to 2 and "GI vs. AA balance" is set to 16, this means that 16 GI samples and 32 direct light samples will be used for each pixel per pass. In some situations it may pay off to reduce one of these values and increase the second one, or even to reduce both. Typically, there is no need to increase "GI vs. AA balance" above 64 and "Light Samples Multiplier" above 4.


Default value should work well in most cases but sometimes it should be increased if there is more noise in direct light areas than in GI.

See: How can I tell whether noise comes from direct or indirect light?


Light Samples Multiplier works in correlation with GI vs. AA balance.

See: GI vs. AA balance



Examples


Example 1

GI vs. AA = 16
LSM = 1
Same number of samples (16) is used for both GI and direct light samples. Noise level is similar in areas affected by GI and direct light.


CESSENTIAL_Direct pass:



CESSENTIAL_Indirect pass:



Example 2

GI vs. AA = 16

LSM = 4


16 samples are used for GI and 16x4=64 samples are used for direct light. There is visibly less noise in direct light pass than in GI pass.


CESSENTIAL_Direct pass:



CESSENTIAL_Indirect pass:



Example 3

GI vs. AA = 64

LSM = 0,25

64 samples are used for GI and 16x0,25=4 samples are used for direct light. There is visibly more noise in direct light pass than in GI pass.


CESSENTIAL_Direct pass:


CESSENTIAL_Indirect pass: