The visual effect of increasing laser labeling exposure time on tangerine peel is shown in
Figure 2-2. At the lowest possible exposure time of 30 µs, the label was faint and hardly visible,
whereas at the highest exposure time of 120 µs, the etch markings merged into solid lines.
Calculations of laser etched surface area were done using Image processing software. In general,
the area covered by the etched markings increased with increase in exposure time (Figure 2-3).
The rate of peel surface area disruption declined at higher exposure times as etch A label code “M1” was etched on fruit surfaces using 18 different exposure times
corresponding to 30 µs to 140 µs label duration (Etxeberria et al., 2006). The energy level used
was the recommended 0.000752 W/dot. To enhance resolution, labels were dyed with fruitbased black color. Five replicates per exposure time were used. Images of the dyed label were
taken using a Canon Powershot S31S digital camera mounted on a Wild Heerbrugg 165083
stereoscope. Surface area altered by the label was measured using an Image Processing
Software. Total area was calculated based on number of pixels within the area covered by the
laser depressions with 1 pixel corresponding to 50 µm
2
.