Fluorescent lamp began with the Geissler tube continued as even better vacuums were produced. The most famous was the evacuated tube used for scientific research by William Crookes. That tube was evacuated by the highly effective mercury vacuum pump created by Hermann Sprengel. Research conducted by Crookes and others ultimately led to the discovery of the electron in 1897 by J. J. Thomson and X-rays in 1895 by Wilhelm Roentgen. But the Crookes tube, as it came to be known, produced little light because the vacuum in it was too good and thus lacked the trace amounts of gas that are needed
Roentgen equivalent man Roentgen equivalent man The roentgen equivalent man (or rem) is an older, CGS unit of equivalent dose, effective dose, and committed dose which are measures of the health effect of low levels of ionizing radiation on the human body. Quantities measured in rem are designed to represent the stochastic biological risk of ionizing radiation; primarily radiation-induced cancer. These quantities are derived from absorbed dose, which in the CGS system has the unit rad which is also an older unit. There is no universally applicable conversion constant from rad to rem; the conversion depends on relative biological effectiveness (RBE). The rem