1) Dermatologic procedure 
Grenz Rays are part of the electromagnetic spectrum comprising low energy (ultrasoft) X-rays. These were first investigated by Gustav Bucky in 1923 using a cathode vacuum tube with a Lithium borate glass window which he labeled Grenz rays as he believed that the biological effects resembled UV light & traditional X-rays and hence was on the border...
X-radiation generated with X-ray tube voltages below about 20 kV
very soft electromagnetic radiation of wavelengths of about 2 angstroms.