Which light rays are considered germicidal?

The correct choice is ultraviolet (UV) rays because they possess the ability to kill or inactivate microorganisms by damaging their cellular structures, specifically their DNA. This germicidal property is harnessed in various applications such as sanitation and disinfection in medical facilities, water purification systems, and products like UV sterilizers. UV rays are categorized into three types: UVA, UVB, and UVC, with UVC being the most effective for germicidal purposes due to its shorter wavelength and higher energy, which leads to stronger penetration and disruption of microbial DNA.

In contrast, infrared rays are primarily associated with heat and do not carry the germicidal properties that UV rays do. Fluorescent rays, while they encompass a broader spectrum of light, are generally not utilized for germicidal purposes. Heat rays also focus on producing thermal energy rather than having a direct impact on microbial life. Thus, UV rays stand out as the effective option for germicidal action within this context.