\subsection{Integrated luminosity measurement}

The experimental conditions at TLEP will be similar to those of LEP, with the additional bonus of very stable beam conditions brought by the continuous top-up injection. Nevertheless, there will be a number of notable differences, as exemplified below.
\begin{itemize}
\item The smaller value of $\beta^*_y$~\cite{cite:1305.6498} increases the beam divergence at the interaction point to the extent that it may have a sizeable effect on the acceptance of low angle detectors used for the luminosity measurement. The better stability of the TLEP beams will help to keep the uncertainty on the beam divergence to a level similar to that evaluated at LEP. 
\item The strong final-focus quadrupoles will generate large amounts of synchrotron radiation, which need to be simulated and against which appropriate shielding must be provided. 
\item An increased amount of beamstrahlung may lead to a somewhat larger background of electromagnetic radiation produced in the interaction region. As mentioned in Section~\ref{sec:beamstrahlung}, it is nevertheless several orders of magnitude smaller than the level expected in a linear collider environment. 
\item The repetition rate in multi-bunch operations will reach 20 MHz at the Z pole. This specificity has to be taken into account in the design of the detectors. 
\end{itemize}

To the extent that the aforementioned issues are properly addressed and solved, there should be no significant difficulty to achieve luminosity measurements with an experimental precision similar to that obtained at LEP, typically a few times $10^{-4}$. At the Z peak it would be of interest to achieve even better precision, e.g., for the measurement of the invisible width hence the number of light neutrinos, which will require a more precise construction of the luminometers. The main limitation on the luminosity measurement, however,  would presently come from the theoretical calculation of the low angle Bhabha cross section. Clearly, progress in this aspect would pay great dividends. 


 