This paper presents the mid-field model for an ultraviolet C light emitting diode (UVC LED) of wavelength around 275±5 nm by comparison of the 2-dimension (2-D) gray-level image captured from a mono-CMOS sensor and simulated irradiance pattern. Because of UVC light, we propose using a fluorescent film to absorb UVC light and re-emit visible light so that the 2-D image could be captured. The analysis and calibration to obtain accurate gray level of image are performed. Finally, we achieve the mid-field model with high accuracy. Furthermore, this model is also applied for dome lens design and then compares the performance with fabricated samples in measurement to expertise its validity.