# Near Infrared Illumination Optimization for Vein Detection: Hardware and Software Approaches
## 3 Results and Discussion
### Evaluation of Near Infrared LEDs Wavelength and Arrangement  
Images captured at different incident wavelengths were processed to evaluate the performance of each LEDs wavelength. The vein was captured as a black line on the picture when exposed to near-infrared radiation [26]. The haemoglobin absorbs the NIR radiation, which causes it to appear darker than other tissues [26]. The image status was denoted as fail (X) and pass (O). Table 4 shows the findings for both arm and palm using either square LED or ring LED arrangement of the NIR light at wavelengths ranging from 720 nm to 940 nm. Fail (X) indicates that the vein images failed to be acquired, and vice versa. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{\((\lambda)\)} & **Arm (Square)** & **Arm (Ring)** & **Palm (Square)** & **Palm (Ring)** \\  & **(9 LEDs)** & **(8 LEDs)** & **(9 LEDs)** & **(8 LEDs)** \\ \hline
**720 nm** & X & X & X & X \\
**760 nm** & X & X & X & O \\
**850 nm** & O & O & O & O \\
**900 nm** & O & O & O & O \\
**940 nm** & O & O & O & O \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Status for arm and palm with wavelength range from 720 nm to 940 nm. Figure 8: Vein counting applied (black line) on the image named CP85M9. The first evaluation focused on the LEDs wavelength, comparing the 720 nm, 760 nm, 850 nm, 900 nm, and 940 nm. Furthermore, each wavelength image was acquired using ring LED and square LED of the LEDs light arrangement. Figures 9 and 10 only show the successfully acquired vein images at ROI of palm and arm areas. The 720 nm wavelength was unable to visualize the vein because the wavelength's penetration depth falls between visible light and near-infrared radiation. The optical penetration of human skin is found to be deepest at wavelengths approaching 1090 nm when tested light penetration for wavelengths ranging from 400 nm to 2000 nm [5]. The light penetration depth in human tissue is mostly affected by the absorption and scattering of light radiation. Moreover, the beam angle of the LEDs limits the area of illumination, as can be seen in Figure 9 (images with labels HP72M9 and HP72R8). The square LED and ring LED arrangement of LEDs modified the radiation intensity distribution. The images in Figures 9 and 10 compared the entire wavelengths in the palm area for square LED and ring LED. Figures 9 and 10 show that the square LED illuminates both palm and arm areas better based on the physical visualization of the images obtained. The image labeled CA90M9 square LED-based has better visualization compared with the image labeled CA90R8. Table 5 shows that an incident wavelength of 850 nm yields the highest number of veins counts with images labeled CA85M9 and CA85R8. Isolated and big vessels were found, especially in the palm area. The peak wavelength of 850 nm has good scattering light propagation characteristics in human tissue, hence providing a better penetration effect [13]. However, little and tortuous structures were better found with wavelengths between 850 and 900 nm. The 900 nm wavelength light created more shadow, which made another line be detected as a vein. The result of 940 nm and 900 nm was similar in terms of vein counts, except the shadow was more obvious at a wavelength of 900 nm. The ring LED arrangement vein counts were higher than the square LED arrangement for the palm area, which was caused by the additional vein counts of the infrared wavelength 760 nm images. The average thickness of the epidermis is 0.2 mm; however, this thickness varies based on the location of the body and the volume of water that the epidermis retains. The dermis is the second layer of skin located underneath the epidermis. This layer is significantly thicker than the epidermis (often 1 to 4 mm) [27]. This sublayer has fewer nerve fibers  
Figure 10: Images for arm area.