# Near Infrared Illumination Optimization for Vein Detection: Hardware and Software Approaches
## 2 Methodology
### NIR Projection
#### 2.1.3 Angle  
The incident light source angle also plays a crucial role in ensuring uniform illumination. LEDs with a very small angle of \(<\)15\({}^{\circ}\) will illuminate isolated areas in a spot way, creating black holes in the center of the FOV which leads to difficulties in the visualization process. On the other hand, very wide angles make the light difficult to focus. Hence, choosing a proper angle for the illumination process is essential. LEDs with an illumination angle of \(>\)30\({}^{\circ}\) were found to be a good angle for the LEDs parameter in line with [PERSON] and [PERSON] finding as illustrated in Figure 2[13]. Based on Table 2, LEDs with an illumination angle of 30\({}^{\circ}\) were utilized in this study.  
The incident light wavelength emitted by the infrared LEDs was first examined using the ASEQ LR1 spectrometer. The absorption spectra were measured with the ASEQ  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Wavelength** & **Specifications** & **Value** \\ \hline \multirow{4}{*}{720 nm} & DC Forward Current & 20 mA \\  & Power Dissipation & 150 mW \\  & DC Forward Voltage & 1.6–2.0 V \\  & Luminous Intensity & 5.46–9.56 cd \\ \hline \multirow{4}{*}{760 nm} & DC Forward Current & 20 mA \\  & Power Dissipation & 150 mW \\  & DC Forward Voltage & 1.6–2.0 V \\  & Luminous Intensity & 6.83–10.93 cd \\ \hline \multirow{4}{*}{850 nm} & DC Forward Current & 200 mA \\  & Power Dissipation & 180 mW \\  & DC Forward Voltage & 1.8–2.3 V \\  & Luminous Intensity & 30.74–92.21 cd \\ \hline \multirow{4}{*}{900 nm} & DC Forward Current & 100 mA \\  & Power Dissipation & 40 mW \\  & DC Forward Voltage & 2.2 V \\  & Luminous Intensity & 6.83–10.93 cd \\ \hline \multirow{4}{*}{940 nm} & DC Forward Current & 100 mA \\  & Power Dissipation & 150 mW \\  & DC Forward Voltage & 1.4–1.8 V \\ \cline{1-1}  & Luminous Intensity & 40.98–58.06 cd \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of LEDs.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Wavelength** & **Angle** \\ \hline
720 nm & 30\({}^{\circ}\) \\
760 nm & 30\({}^{\circ}\) \\
850 nm & 30\({}^{\circ}\) \\
900 nm & 30\({}^{\circ}\) \\
940 nm & 30\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Angle of illumination of LEDs.  
Figure 2: LEDs with an angle of illumination at (**a**) 30\({}^{\circ}\) (**b**) 15\({}^{\circ}\).  
LR1 spectrometer (200-1200 nm, 2 nm resolution with 50 \(\upmu\)m slit) featuring a Toshiba TCD1304 DG linear array (3648 pixels). The spectrometer was coupled with the ASEQ light source and ASEQ fiber-optics probe consisting of two fibers, one for excitation and one for collection. The fiber optic connector is SMA 905 to 0.22 numerical aperture with single-strand optical fiber. The absorption spectra of the LEDs were acquired with the ASEQ LR1 system.  
The ASEQ LR1 spectrometer software was utilized to plot the wavelength captured by the instrument to verify the actual light wavelength output as emitted by the LEDs. Before the wavelength readings were taken, the instrument was first calibrated prior to this study to remove the noise from the surrounding light. Figure 3 shows the measured actual wavelength spectra of the selected NIR. Referring to Figure 3, the wavelength validation for (a) 720 nm, (b) 760 nm, (c) 850 nm, (d) 900 nm, and (e) 940 nm showed the wavelength emitted by the selected LEDs has a correct range of peak value.  
Figure 3: The wavelength spectra for LED wavelength of: (a) 740 nm; (b) 760 nm; (c) 850 nm; (d) 900 nm; and (e) 940 nm.