Aesthetic laser marking assessment using luminance ratios

In this paper, a luminous ratio was applied to evaluate four types of material surfaces; anodized aluminium, stainless steel, poly-butylene tetra-phthalate (PBT), and phenol formaldehyde, marked using a Nd:YAG laser. The luminous ratio was based on the spectral reflectance readings obtained from a spectrophotometer and computed for the case of scotopic (low illumination) and photopic (normal illumination) viewing. The method of using luminous ratios was able to produce quantitative results that determined visibility differences under photopic and scotopic viewing for stainless steel and phenol formaldehyde. The method revealed optimal marking speeds for all the materials studied; with the optimal speed found to be highest for PET and lowest for stainless steel. By comparing the absolute luminous ratio differences at the respective optimal marking speeds, the method also revealed that markings on phenol formaldehyde and anodized aluminium had the highest and lowest visibility, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.