阿彌陀經通贊疏 3.43

3.43

無量相者，相好無量故。無量幢者，身量功德高而復峻由如幢也。大光者，身智二光無不照故。大明者，得佛三明無不知故，即正遍知也。寶相者，內外二相皆可寶重故。淨光者，淨者無漏。光者身智二光，故言淨光也。

As for 'Amitaketu,' it is because his marks and signs are limitless. 'Amitadhvaja': his bodily dimension and merit are high and lofty, just like a banner. 'Mahāprabha': because the two lights of body and wisdom illuminate everywhere. 'Mahāprabhāsa': because he has attained the Buddha's three clarities and there is nothing he does not know, which is the correct and universal knowledge. 'Ratnaketu': because both his internal and external marks are worthy of treasure and veneration. 'Śuddhaprabha': 'pure' means uncontaminated (anāsrava); 'light' means the two lights of body and wisdom; hence he is called Pure Light."