yes, the suttas mention the perception of light in the two contexts referred to by B. Analayo. In the hindrance removal formula, it seems to appear as an antidote to 'dullness & drowsiness', just as loving-kindness is mentioned for ill-will, inner tranquilisiation of the mind for excitement and worry, and unperplexity about wholesome states in the case of doubt.
However, elsewhere the Buddha rather mentions 'ārambhadhātu nikkamadhātu parakkamadhātu' which according to PTSD are synonyms for viriya. The reason for this might be that in the beginning it is not possible to focus on the light as one generally does not perceive it, but one can surely make an effort!
The Patisambhida magga recommends alokasañña to fight out dullness and drowsiness. And at AN 4.41 for example, the perception of light, together with divasañña (a rather obscure term ThanB translates as 'perception of daytime [at any hour of the day]', the Atthakatha says it refers to the previously mentioned alokasañña and the Tika says it refers to the sunlight and the moonlight! [if I am not mistaken]) is said to lead to 'knowledge and vision'.
So I want to know what Goenkaji has to say about it. I know that in one ten-day course's discourse he says that during is own first course he saw the light, but that his teacher had told him not to pay any attention to it. And on the other hand, those practicing according to the visuddhimagga use it a lot. So I am trying to understand where the contradiction lies.
Where knowledge ends, religion begins. - B. Disraelihttp://www.buddha-vacana.org
As a sweet-smelling and beautiful lotus flower may grow upon a heap of rubbish thrown on the highway, so also, out of the rubbish heap of beings may appear a disciple of the Buddha, who with his wisdom, shines resplendent in wisdom. -/ Dhp 58-59