One must definitely perform Sandhyavandanam only after wearing the Thiruman Kappu. During periods of ritual impurity, it is best for children or individuals without impurity to light the lamp. Some say that if no such person is available, those who are impure can light the lamp themselves. Others suggest standing at a distance to light it, and after that period (theetu kalam), we can purify it and take the lamp. However, one must not light the lamp placed directly inside the Perumal sannidhi, nor go near it. All the alternative options mentioned above apply only if the lamp is not near the Perumal sannidhi.