A value of 100 IRE was originally defined to be the range from blanking level to peak white in a video signal. A value of 0 IRE corresponds to the voltage value of the signal during the blanking period. The sync pulse is normally 40 IRE below this 0 IRE value, so the total range covered from peak to trough of an all white signal would be 140 IRE. 
Note that video signals use the "IRE" unit instead of DC voltages to describe levels and amplitudes. Based on a standard 1 Vpp NTSC composite-video signal that swings from -286 mV (sync tip) to +714 mV (peak video), a 140 IRE peak-to-peak convention has been established. One NTSC IRE unit is 7.14mV, where -40 IRE is equivalent to -286 mV, and +100 IRE is equivalent to +714 mV. Note that 0 IRE is equivalent to 0 V. The Black Level is equivalent to 53.57 mV (7.5 IRE)
The PAL video signal is slightly different in that it swings from -300 mV to +700 mV, instead. Thus, one PAL IRE unit is 7mV, where -43 IRE is equivalent to -300 mV at the sync tip, and +100 IRE is equivalent to +700 mV at the peak video level. Black level is the same as the blanking level 0 mv (0 IRE) 
- Robin & Poulin; Michael Robin; Michel Poulin (2000). Digital television fundamentals: design and installation of video and audio systems. McGraw-Hill Professional. p. 17. ISBN 0-07-135581-2.
- "World Analogue Television Standards and Waveforms". Retrieved 31 May 2018.
- "Composite Video Signals (CVBS)". National Instruments. Retrieved 31 May 2018.
- Cliff Win, Jr. "Measuring composite-video signal performance requires understanding differential gain and phase, Part 1 of 2". National Semiconductor Corporation. Retrieved 31 May 2018.
- "Vertical Blanking Interval of 625-Line Standard (PAL Colour)" (PDF). Archived from the original (PDF) on 28 April 2016. Retrieved 3 September 2015.
- "BT.470 : Conventional analogue television systems". International Telecommunications Union. Retrieved 28 August 2012.