We report the change in optical absorption properties of InGaN epilayers around the critical layer thickness determined from X-ray diffraction. Detrimental sub-band gap absorption is observed in InGaN thin films grown beyond the critical layer thicknesses, and is caused by localized electric fields around extended crystalline defects and aided by V-defects through light channeling. The photoluminescence response from InGaN thin films, grown beyond the critical layer thickness, is reduced owing to absorption of the incident laser light by non-radiative recombination extended crystalline defects. The formation of V-defects is observed to occur beyond the critical layer thickness and continues to grow in areal coverage aiding in sub-band gap absorption. This optical behavior sets constraints to be incorporated in the design of InGaN solar cell and requirement for improvement in epitaxial growth techniques to reduce V-defects. (C) 2012 Elsevier B.V. All rights reserved.