An important issue, almost ignored in the chameleon husbandry is the question of the direction of the light.
The only source of all kinds of rays in the wild is the Sun.
Chameleons, how ever strange it sounds, tend to hide from the direct exposure to sun-rays the most of the day and expose themselves to it actively only in the early morning and late afternoon hors and this usually not long, for several minutes only.
What is the direction of sun-rays exposure in the morning, when the sun stays low above the eastern horizon?
From the SIDE!
What is the direction of sun-rays exposure in the late afternoon, when the sun stays low above the western horizon?
From the SIDE!
And where do the chameleons perceive the light during the majority of the day from, when they sit in the bushes and trees, enjoying shade, effectively hidden under the "umbrella" of the mostly horizontally exposed leaves (that get with the right-angle position towards the sun-rays the maximum exposure to the rays, necessary for photosynthesis)?
From the SIDE!
Therefore, the predominant direction of light, they get exposed to, is from the side (sic!) and NOT from above, as is commonly believed.
What do we do as a rule in captivity now?
Well, in general, for practical technical reasons, and because of many precedences, we mostly put the light sources (of all spectrum from IR, through visible light to UV) ON or ABOVE the top of the cage and let them shine DOWN.
This position of lights, as stated above, is therefore NOT natural, at least not for the whole of the day physically and in general (the sun changes the position during the day obviously, so at least 2/3 of the day, the direction of sun exposure is NOT from more-or-less above but either diagonally or from the side), and for the predominant exposure of chameleons to sun-rays (from the side) in particular.
What does it cause?
Anything unnatural causes more or less discomfort. And light, delivered through sun-rays in all the wide spectrum is essential for life!
The chameleons can not efficiently bask, as when they bask, they flatten their bodies and expose them in the right angle to the direction of the rays. The "pancaking" however, is done usually vertically or inclined towards one or another side a bit but never (or almost never) horizontally.
This is also why while basking, the captive chameleons often burn their casques and dorsal crests. They do not expose the side, but back, same as in the wild!
The position of basking horizontally pancaking, I have never seen in my 30plus years of field research in the wild. It is unnatural, as it is not stable! Chameleons hardly can stay long with their flattened body in horizontal position holding a branch from the side!
LACK OF UV
Unfortunately, in captivity, we face a phenomenon that will never be solved, as it is technically impossible. The intensity of light reduces with the square of the distance from the source.
Sun is so far, that the difference in light intensity up in the canopy and down on the earth (if not blocked or shaded) is immeasurable. But, the sources of artificial light of all spectral compositions are positioned in single or tens of centimetres from the chameleon.
Most UV sources give efficiently UVI=0 just 7-10 (max about 25 in very strong ones) underneath them as we put them on the mesh on the top of the cages (the mesh can also absorb lots of light) or even on the glass (which absorbs almost 100% of the UV straightaway) - while if the chameleons get too close, they get long healing burns!
LACK OF VISIBLE LIGHT
If the light sources are situated on the top, most of the cage, (especially if naturally densely equipped with living plants and branches) is in such a shade, that chameleons do not see anything and they also very often refuse to stay in the lower 30% of the volume of the cage... Very often, people are confused why their chameleon does not eat the crickets crawling around the bottom of the cage, especially in indoor captive conditions.
This is why:
They do not see them!
They sit close to the light source and adapt the pupils to the high intensity there and the 50times and less intensity of light at the bottom will make the objects there almost invisible. Try it yourself! Stay two-three minutes one feet from a light bulb and then try to see what is on the bottom of the cage... you will see nothing!
Most of our chameleons in captivity get to close to IR light sources and get overheated. Why? Because they have no inborn security/regullation mechanism. They can not get too close to the sun! But they can very well get too close to the bulb!
And they do.
And they overheat.
And they speed up their metabolism.
And they age quicker.
And they become infertile (low temps are necessary for spermatogenesis - Here we go, dear panther breeders: why dominant males, firing up so beautifully in sun, loose sexual appetite and do not even mate and if they mate, their offspring is so often miserable? They bask too much, you keep them too warm...).
And they get sick due to thermal discomfort.
And the parasital diseases break out, that would easily stay dormant at low temperatures.
And they die young, not reaching the possible age in captivity.
What to do?
A tricky question...
First of all, learn from Mother Nature and think!
And consider this!
I can say what I do.
And maybe you get inspired...
And make the proper decision...
I put heat lamps to the corner of the ceiling of the cage and let them shine diagonally.
I put lower output (not hot) sources of UV INTO the cage, not above and place them vertically.
I put lights with low heat emissions vertically into the high cages and illuminate one ore even two cages at once.