Direct-conversion radio receivers can offer highly integrated low-cost hardware solutions for spectrum sensing in cognitive radio systems. However, these receivers are susceptible to radio frequency (RF) impairments, such as in-phase and quadrature-phase imbalance, low-noise amplifier nonlinearities and phase noise, which limit the spectrum sensing capabilities. In this paper, we study the joint effects of RF impairments on energy detection based spectrum sensing in multi-channel environments. In particular, we provide an analytical framework for the evaluation of the probabilities of detection and false alarm, assuming Rayleigh fading and approximating the joint effects of RF impairments by a Gaussian distribution. Numerical results illustrate the detrimental effects of RF imperfections on the spectrum sensing performance, which bring significant losses in the spectrum utilization.