Having just been surrounded by angels, filled with the Holy Ghost, and having just prayed again, the Twelve were transfigured such that their entire bodies exuded the brilliance of resurrected beings. Truman Madsen explains this process:
"Artists have often depicted this recognition of light as divine beauty by the halo, the nimbus, and the golden circle above the head. But that is at best a token of the promise and the actuality. For 'whole bodies' are promised illumination, and the light not only hovers over but also surrounds and engulfs the entire personality until it is gloriously beautiful. It was, after all, every one of the multitude, and all of each of them, even the seams of their clothing, that became scintillant with white light in the presence of Christ during that 'ineffable outpouring of prayer,' as Elder James E. Talmage calls it, in the 3 Nephi narrative (see 3 Nephi 19:25). Modern men and women of God who have witnessed such radiance of soul say it is 'like a search light turned on within.' It is 'the same glorious spirit,' the Prophet once wrote, 'gives them the likeness of glory and bloom. … No man can describe it to you-no man can write it.' (Teachings, p. 368) Aesthetic delight, then, whatever else it is, is delight in light. And it is surely significant that the whole color spectrum, every vivid color of the rainbow, harmonizes in white light which, in turn, harmonizes in Christ." (Truman G. Madsen, The Radiant Light, p. 26-7)