If the light is stopped by the power of samyama, then one can become invisible.
Verse 3.21
कायरूपसंयमात् तत्ग्राह्यशक्तिस्तम्भे चक्षुः प्रकाशासंप्रयोगेऽन्तर्धानम् ॥२१॥
kāya-rūpa-saṁyamāt tat-grāhyaśakti-stambhe cakṣuḥ prakāśāsaṁprayoge-'ntardhānam ॥21॥
By control over the subtle body, the yogi can suspend at will the rays of
light emanating from himself so that he becomes invisible to onlookers. He
may again make himself visible by bringing back the power of perceptibility.
Verse 3.22
etena shabdadyantardhanamuktam
By what has been said the disappearance of sound and other tanmatras can be understood.
When the yogi performs samyama on his own body, then suddenly the power of receiving the form stops and there in no contact between the eyes of observers and the body of the yogi. He thus becomes invisible. This is a well-known siddhi or psychic power. It is a frightening practice.
When a form dissolves before
one’s eyes, it is as frightening as the coming of death. An object becomes visible when the light rays reflected from its surface enter the eye of an observer.
If the light is stopped by the power of samyama, then one can become invisible.
In yoga there are five tanmatras or subtle forms of the elements. The roopa tanmatra becomes the object of the yogi’s samyama. First the yogi practises samyama on his body with a mirror, then there is suspension of the power of receiving roopa, or form. For some time there is no contact between the observer and the body of the yogi.
Thus, the physical body first becomes invisible to the yogi himself and afterwards through practice it becomes invisible to others. This is because there is no connection between the object and the observer. Thus this involves meditation on the physical form as seen in a mirror.
By practising samyama on your own form, you can make yourself invisible.
Now in this sutra it is said that in the same manner, by performing samyama on sound, touch, taste, etc., those faculties can be made to disappear. In a similar way, the yogi can stop other sensations also and control the phenomena concerning them.
PATANJALI YOGA SUTRAS