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The mechanism of beam loss and radiation hot spots at the Taiwan Light Source (TLS) and Taiwan Photon Source (TPS) are studied using various types of beam loss monitors (BLMs). The performance of readout devices and the system integration are also presented in this paper. At the TLS, the high beam loss spots downstream of the superconducting wigglers comes from the vertical aperture limit. The highest radiation is detected after the injection section and comes mainly from X-rays generated by the superconducting wavelength shifter installed between the 3rd and 4th kickers. At the Taiwan Photon Source, the high radiation spots are located before the second bending magnet and straight section because there are photon absorbers nearby to contain synchrotron radiation. In order to enhance the sensitivity to beam loss, 1-mm thick lead is used to shield synchrotron radiation to the BLM. The beam loss coming from scattering occurs downstream of the following bending magnet in a poor vacuum region for inelastic scattering and after vertical aperture limitation for elastic scattering. During routine operation in which the beam loss mainly comes from intra beam scattering during decay period, the beam loss pattern varies with the gap and phase of the insertion devices especially for the narrowest gaps. These BLMs are used to adjust skew-quads or sextupoles to minimize the beam loss for maximum beam lifetime. The precise beam energy of the TPS is also calibrated using spin-depolarization in which the beam losses are detected by scintillation detectors. The energy stability during continuous routine operation can be kept to within 10−5 by radio frequency adjustments and fast orbit feedback.