We perform the mid-field model of a UV-C LED with an arranged wavelength of around 275 nm by comparing the 2-dimension (2-D) gray-level image captured by a monochromatic CMOS and the corresponding simulated irradiance pattern. Owing to UV-C light, we propose using a fluorescent film to absorb UV-C light and re-emit light at a longer wavelength so that the 2-D gray level image can be captured. The calibration to approach the corrected gray level of image is presented. Consequently, we obtain the precise mid-field light source model. Moreover, the model is also applied for dome lens design and then compares the optical behavior with fabricated samples in measurement to evaluate its validity.