Described herein is a phantom device that simplifies usage, testing, and development of light imaging systems. The phantom device includes a body and a fluorescent light source internal to the body. The body comprises an optical material designed to at least partially resemble the optical behavior of mammalian tissue. The phantom device has many uses. One use of the phantom device permits testing of tomography software in the imaging system, such as software configured for 3D reconstruction of the fluorescent light source. Another use tests spectral unmixing software in the imaging system. The phantom device also allows a user to compare trans- and epi-fluorescent illumination imaging results.