In a thin-film transistor-liquid crystal display, screening that plays an important role in detecting manufacturing process faults before processing the next step is highly important to improve a total yield and reduce the cost. Present testing that applies to the electrical signal and uses red light has a weakness in detecting an amorphous-silicon (a-Si) residue due to the residue of the incident light being less sensitive. From studies, we have found that a-Si residue is highly sensitive to green light such that the leakage of photocurrent occurs responding to the light. Therefore, we use the green light in an array testing system in addition to red light used in conventional systems. Consequently, a detecting ratio of the a-Si residue is improved by more than 90% compared to the conventional array testing system. (c) 2005 Elsevier B.V. All rights reserved.