"U-rays" are likely a misspelling of "UV rays" or "ultraviolet rays". UV rays have many uses, including:
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Medical applications: UV rays are used to sterilize and disinfect medical equipment, kill bacteria and viruses in the body, and treat skin conditions like acne, eczema, psoriasis, and vitiligo.
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Industrial applications: UV rays are used in industrial processes like curing inks and resins, sterilizing food and beverages, and detecting counterfeit bills.
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Other uses: UV rays are also used in tanning beds, insect traps, and security systems.
