Yes with @hypn0s’ answer, light is very important to traditional astrology. However, this does not always apply. For example, the Head and Tail of the Dragon (The North and South Nodes of the Moon) are considered to cause great effects, yet they do not exert any light, nor are they material bodies, but instead are “imaginary points” in space. It is a similar case with the Parts, such as the Part of Fortune, which is not at all material or project any light, along with the other Parts, yet cause great effects when employed, or show many important things at any given time.
On the heat, that also shows us that the effects do not proceed from the material bodies of the stars and planets, but we are observing the Stars and Planets from our point of view, and from that point, are revealing the higher spiritual cycles at work. Here is what Plotinus (Who was a 2nd Century AD Platonist Philosopher) says which touches on heat (Some astrologers in those days argued that the heat of the Planets are what causes events in this world. Plotinus argues how absurd this is in this chapter as well):
"Then there is the notion that the moon, in conjunction with a certain star, is softened at her full but is malignant in the same conjunction when her light has waned; yet, if anything of this order could be admitted, the very opposite would be the case. For when she is full to us she must be dark on the further hemisphere, that is to that star which stands above her; and when dark to us she is full to that other star, upon which only then, on the contrary, does she look with her light. To the moon itself, in fact, it can make no difference in what aspect she stands, for she is always lit on the upper or on the under half: to the other star, the warmth from the moon, of which they speak, might make a difference; but that warmth would reach it precisely when the moon is without light to us; at its darkest to us it is full to that other, and therefore beneficent. The darkness of the moon to us is of moment to the earth, but brings no trouble to the planet above. That planet, it is alleged, can give no help on account of its remoteness and therefore seems less well disposed; but the moon at its full suffices to the lower realm so that the distance of the other is of no importance. When the moon, though dark to us, is in aspect with the Fiery Star she is held to be favourable: the reason alleged is that the force of Mars is all-sufficient since it contains more fire than it needs.
The truth is that while the material emanations from the living beings of the heavenly system are of various degrees of warmth- planet differing from planet in this respect- no cold comes from them: the nature of the space in which they have their being is voucher for that.
The star known as Jupiter includes a due measure of fire [and warmth], in this resembling the Morning-star and therefore seeming to be in alliance with it. In aspect with what is known as the Fiery Star, Jupiter is beneficent by virtue of the mixing of influences: in aspect with Saturn unfriendly by dint of distance. Mercury, it would seem, is indifferent whatever stars it be in aspect with; for it adopts any and every character.
But all the stars are serviceable to the Universe, and therefore can stand to each other only as the service of the Universe demands, in a harmony like that observed in the members of any one animal form. They exist essentially for the purpose of the Universe, just as the gall exists for the purposes of the body as a whole not less than for its own immediate function: it is to be the inciter of the animal spirits but without allowing the entire organism and its own especial region to run riot. Some such balance of function was indispensable in the All- bitter with sweet. There must be differentiation- eyes and so forth- but all the members will be in sympathy with the entire animal frame to which they belong. Only so can there be a unity and a total harmony.
And in such a total, analogy will make every part a Sign" (Plotinus, Second Ennead, Third Tractate, Chapter 5, Translated by Stephen Mackenna and B. S. Page)
Plotinus argues that the stars and planets themselves are not causes, but this entire cosmos is one unified living being, with all things being linked together, like a chain with many links.
"6. But that this same Mars, or Aphrodite, in certain aspects should cause adulteries- as if they could thus, through the agency of human incontinence, satisfy their own mutual desires- is not such a notion the height of unreason? And who could accept the fancy that their happiness comes from their seeing each other in this or that relative position and not from their own settled nature?
Again: countless myriads of living beings are born and continue to be: to minister continuously to every separate one of these; to make them famous, rich, poor, lascivious; to shape the active tendencies of every single one- what kind of life is this for the stars, how could they possibly handle a task so huge?
They are to watch, we must suppose, the rising of each several constellation and upon that signal to act; such a one, they see, has risen by so many degrees, representing so many of the periods of its upward path; they reckon on their fingers at what moment they must take the action which, executed prematurely, would be out of order: and in the sum, there is no One Being controlling the entire scheme; all is made over to the stars singly, as if there were no Sovereign Unity, standing as source of all the forms of Being in subordinate association with it, and delegating to the separate members, in their appropriate Kinds, the task of accomplishing its purposes and bringing its latent potentiality into act.
This is a separatist theory, tenable only by minds ignorant of the nature of a Universe which has a ruling principle and a first cause operative downwards through every member.
7. But, if the stars announce the future- as we hold of many other things also- what explanation of the cause have we to offer? What explains the purposeful arrangement thus implied? Obviously, unless the particular is included under some general principle of order, there can be no signification.
We may think of the stars as letters perpetually being inscribed on the heavens or inscribed once for all and yet moving as they pursue the other tasks allotted to them: upon these main tasks will follow the quality of signifying, just as the one principle underlying any living unit enables us to reason from member to member, so that for example we may judge of character and even of perils and safeguards by indications in the eyes or in some other part of the body. If these parts of us are members of a whole, so are we: in different ways the one law applies.
All teems with symbol; the wise man is the man who in any one thing can read another, a process familiar to all of us in not a few examples of everyday experience.
But what is the comprehensive principle of co-ordination? Establish this and we have a reasonable basis for the divination, not only by stars but also by birds and other animals, from which we derive guidance in our varied concerns.
All things must be enchained; and the sympathy and correspondence obtaining in any one closely knit organism must exist, first, and most intensely, in the All. There must be one principle constituting this unit of many forms of life and enclosing the several members within the unity, while at the same time, precisely as in each thing of detail the parts too have each a definite function, so in the All each several member must have its own task- but more markedly so since in this case the parts are not merely members but themselves Alls, members of the loftier Kind.
Thus each entity takes its origin from one Principle and, therefore, while executing its own function, works in with every other member of that All from which its distinct task has by no means cut it off: each performs its act, each receives something from the others, every one at its own moment bringing its touch of sweet or bitter. And there is nothing undesigned, nothing of chance, in all the process: all is one scheme of differentiation, starting from the Firsts and working itself out in a continuous progression of Kinds." (Plotinus, Second Ennead, Third Tractate, Chapter 6-7, translated by Stephen Mackenna and B. S. Page)