The whole practice, in one sentence.
"What you really need to do to correctly practice absorbing the essence of light is to simply imagine the light of the sun or moon in your body. This is a method much used in hatha yoga, and anyone can do this."1
Imagine the light inside you. Not out there, not entering — in the body already.
And it is placed anywhere you want it: "You just imagine the light of the sun or moon wherever you need it in your body, and then you need not try to absorb any chi essences from outside."1
Which makes it one of the few practices here with a target you choose. Most of the methods are whole-body or centre-line by design. This one is directable: you put warmth or coolness where it is wanted.
It is named as an early-stage practice — "yet another cultivation practice used at the early stages of the path"1 — so it belongs before the heavy channel work rather than during it.
There is a selection rule, and it is the most immediately usable line on the page.
"If you're weak you try to imagine the light of the sun inside you, and if you have too much energy, you 'cool off' by imagining moonlight within."1
Depleted → sunlight. Overcharged → moonlight.
Which makes this a regulator, not an accumulator. The point is not to collect as much as possible; it is to move toward balance from whichever side you are on.
That matters, because too much energy in an unprepared system is the standard way this whole path goes wrong — and here is a cheap, directable method for taking the edge off it. See The Premature Valve.
A regulator also has to be available when the imbalance is, which is the practical argument against the calendar below.
The received Taoist version of this practice is hedged with timing rules.
"In these absorption practices, mentioned in the book Can Tong Chi by Wei Bo Yang, it is related that you should only try to absorb the yin light of the moon around the fourteenth to sixteenth day of the lunar calendar when the moon is full, for at other times the practice is virtually worthless. Practitioners try to absorb the yang light energies of the sun only from the first to third days of the lunar month, too, so if there is a cloudy day or rainy weather during these periods then you are out of luck. You don't have many chances during the year to practice this sort of technique."1
Three days a month for moonlight. Three for sunlight. Minus weather.
And the rules are unnecessary, because the exposure was never the operative part:
"You don't need to go and physically see the sun or moon to 'absorb their essences' because you are always absorbing their energies anyway… The sun's energies are always passing through you, even if you are inside a house, but practitioners didn't understand this when reading the early Taoist books that mentioned these techniques."2
The diagnosis given is a reading error, not a lost teaching: the texts described something about light, readers assumed a scheduled encounter was required, and the calendar grew around an operation that was always internal.
A second form of the same practice, with a different object and no timing at all.
"In Shakyamuni's day, every monk was told to imagine that their mind and body became only sunshine as they were falling asleep, which is also an excellent related cultivation technique."2
Note what changes. You are not imagining light in the body. You are becoming light — mind and body both, nothing left over.
And the timing is the one moment everybody has: falling asleep, nightly, requiring no scheduling and no additional session.
Which makes it the cheapest practice named anywhere in this material — it costs nothing, occupies time already spent, and was reportedly given to everyone rather than to an elect.
The material distinguishes three practices that get confused with each other, and separating them tells you what each is for.
Absorbing external essences. The Taoist calendar version — go out, encounter the sun or moon, take something in. This is the one being deflated.
Imagining light within. The recommended version — sunlight or moonlight placed in the body, chosen by state, available always. A regulator.
Becoming only light. The monks' version — no light-in-a-body, because there is no body left in the image. This is closer to the formless practices than to the other two.
And a fourth is mentioned in passing: "the practice of visualizing rainbows can also be used in concentration practice, which helps open up the chakras and chi channels if a stable mind is attained."3
The stated difference between the first family and the light-of-sun-and-moon family: "the idea behind visualizing the light of the sun and moon is to help transform the body's chi and consciousness as well"3 — colour kasinas train stability, and light work is claimed to do that and act on the chi.
Notice which way you are off. Flat, cold, depleted — or wired, hot, overfull. That decides the object.
Put the light where it is needed. Sunlight for the first, moonlight for the second, placed in whatever region wants it. You are not drawing anything in from outside; you are imagining it already there.
Do it whenever. No calendar, no clear sky, no window. The energies are passing through you indoors, and the connection is made through the mind.
Then release it, like any visualization. "In visualization practice you try to reach a stable state of consciousness by concentrating on an image, and then let go, and that resultant state of emptiness leads to transformations in your chi and channels. This is what we are ultimately after."2 The light is scaffolding; the emptiness after it is the point. See Visualize Then Release.
And take the sleep version for free. Falling asleep, let mind and body become only sunshine. It costs nothing and it was, on this account, standard issue.
There is a limit on how far the light image can be pushed, and it is stated as a fact about the exercise.
"It is hard to visualize endless boundless light, and the only way you can approximate anything like that is by reaching a state of infinite emptiness."3
Which is a useful piece of practical instruction hiding in a metaphysical sentence. If you try to make the light limitless, you will fail — the mind cannot hold an unbounded image.
And the failure has a destination. What you can reach instead is emptiness without edges, which is what the boundless-light image was pointing at all along.
So the light practice has a natural terminus: it works while the image is bounded and placed, and when you reach for boundlessness the image drops out and something else takes over. That is not a breakdown of the method; it is the method handing off. See Cessation and Witnessing Explain the Overlap.
The physical picture underneath the deflation is worth having, because it is what makes the calendar unnecessary.
"We are always absorbing the light of the sun, moon, stars and planets. Our physical bodies, with chi channels and chakras inside, are like molecules that absorb the light energies of the universe. Externally, one frequency of light causes our physical body to make vitamin D while another causes it to tan. Inside of us, who knows what those then invisible energies are responsible for doing?"2
A known case is offered as the model: one band of light drives a chemical synthesis in the skin, another drives pigment. Different frequencies, different specific effects, no perception required — none of it depends on you looking at the sun.
The extension beyond that is marked as speculation — who knows — rather than asserted.
What survives without any speculation is the operational point: there is no window of opportunity to miss. The connection is made through the mind, at any hour, indoors.
Evidence. [PRACTITIONER SOURCE]. 🚩 SECONDARY WITHOUT PRIMARY — the Cantong qi is named and not quoted, hedged as it is related that; the attribution to Shakyamuni's day has no source. 🚩 SINGLE SOURCE. [PLAUSIBLE — needs corroboration].
Tension — always absorbing, and needing to practise. If the energies pass through you continuously, the practice cannot be about acquiring them; what it is about instead is stated only as connecting through the mind.
Tension — regulator and scaffolding. The sun/moon selection makes this a balancing tool applied where needed; the release instruction makes it one more object to drop. Those are different reasons to use it and imply different session lengths.
Open question — does the Cantong qi actually specify those days? The hedge is the source's own, and the whole reading-error diagnosis rests on what the text says.
Open question — how long? No duration is given for the light practice, at either the placement stage or the release.
Two accounts of what the light is doing, and they lead to different practices.
It is an object like any other. You hold it, the mind stabilises, you let go, and the emptiness does the work — in which case sunlight is interchangeable with a white disc or a skeleton, and the sun/moon distinction is flavour.
And it is specifically warming or cooling. Sun for depletion, moon for excess, placed where needed — in which case the object is not arbitrary at all, and choosing wrongly would push you further off balance.
The first is the general position on visualization; the second is the specific instruction given here. A practitioner following the first uses whichever image holds most stably. One following the second checks their state first and picks accordingly — and only the second treats the practice as a regulator, which is the thing that makes it worth having in the toolkit at all.
False Scarcity — behavioral mechanics.
An artificial limit changes behaviour as powerfully as a real one. A purchase cap raised consumption by a quarter in a field study where supply was never constrained; "sold out" labels raise perceived value even when stock is fine. The mechanism: scarcity is read as a signal of value — if it were worthless, it wouldn't be restricted.
Two things follow for a practice hedged by a calendar.
The restriction revalues the practice, not just the access. Three days a month, weather permitting, makes the technique feel consequential in a way that do it any night before sleep cannot — regardless of what it does.
And the effect does not require anyone to have manufactured the limit deliberately. A misread text produces exactly the same scarcity, and exactly the same inflation of value, with nobody intending it.
Which explains something otherwise puzzling: why a correction this simple could go unmade for a very long time. The calendar was doing real work — it made the practice demanding, countable, and visibly serious. Missing a window was a loss you could feel. Trading that for imagine it whenever you like is a downgrade in everything except effectiveness.
The usable test, and it generalises well past moonlight: when a practice has access rules, ask what the rules are protecting. Some limits track a real constraint — the day of rest between unwinding sets, the preliminary work before concentrated methods. Others track nothing and persist because restriction feels like significance. The tell is whether anyone can say what goes wrong if you ignore it — and here, the answer is nothing.
What the source leaves undetermined is whether the light image is doing anything the emptiness after it isn't.
The claim is that sun and moon work transforms "the body's chi and consciousness as well" — that is, more than a plain concentration object does. Which would make the light special.
And the stated mechanism is the general one: concentrate, stabilise, release, and the resulting emptiness transforms the chi and channels. That mechanism has no light in it. It is the same for a skeleton, a colour, or a deity.
So either the light contributes something during the holding phase — in which case the sun/moon selection rule is meaningful and this is a genuinely different practice — or it does not, in which case imagine sunlight when depleted is a placebo dressed as physiology and any object would serve.
The regulator instruction only makes sense on the first reading. The release instruction only makes sense on the second. Both are given, a paragraph apart, and which one is right decides whether you choose your object by your state or by what holds steadiest.