“The Light” is episode eighteen of season four of Stargate SG-1.
Whilst the stargate is opening, a member of one of the other SG teams throws himself into the vortex as it opens, killing himself (throwing yourself into the burst of energy that erupts from a stargate is not good for you). He had been acting slightly, although almost unnoticeably, oddly before he committed suicide, and had just been on a mission with Daniel.
They had been studying an abandoned Goa’uld palace with one room with an unusual hologram in it. There were some unusual writings in the palace which Daniel and Teal’c are attempting to translate. Daniel, too, starts behaving a bit oddly, being desperate to get back to the palace. Then he, too, tries to commit suicide.
The holographic light seems to be affecting people – and not in a way that’s conducive to long-term health.