A Linear Light can be sub-divided into multiple light sources - which causes the illumination from the light to be more even, and causes the light to converge faster (fewer passes) when rendering.
Linear Light (bottom) and Rectangular Light (top) after 20 rendering passes.

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i have checked my version of irender.
IRender nXt Version Information
The latest version of IRender nXt is JD13nxt - built April 13, 2010
You are running version: 3.0 JD13nxt - built April 13, 2010
If you replace a long rectangular light of 100 watts with 8 shorter lights make them 12.5 watts each (100/8)