The influence of the sparsity of random speckle illumination on traditional ghost imaging (GI) and GI via sparsity constraint (GISC) in a noise environment is investigated. The experiments demonstrate that both GI and GISC obtain their best imaging quality when the sparsity of random speckle illumination is 0.5, which is also explained by some parameters such as detection of the signal to noise ratio and mutual coherence of the measurement matrix.