The optical transmission response of the Spinlab HVI 900 fibrograph has been examined using neutral density filters, fibrograph calibration sheets, and melt blown fabrics. Neutral density filters generate a basic linear response when the log,(IJI) functional response is plotted against the diffuse density values. However, the cellophane sheets and the fibrous webs produce curvatures that indicate that calibration of the fibrograph is highly sensitive to the material used in calibration. The fiber geometry is important to overall transmitted light behavior.