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Light and Dark

Updated: 5 days ago

It is the ever-evolving relationship between good science and vastly improved technology that holds the key to the next wave of improvements for captive exotic animals. If we, as keepers, implement these things in a timely matter, we will see fewer occurrence of avoidable disease, and we will; further witness longer, healthier lives and benefits from dedicated species-specific enrichment and, therefore, better reproductive and survival rates going forward.

forest floor

One of the ways in which we can work smartly to provide any given species with everything that it requires to thrive is to offer a dedicated and measured area of enclosure in which the animal can choose to obtain the average wild solar index or "quantity" of UVB that is common to that species. Of course, every species uses sunlight in a different way: some are nocturnal, some crepuscular and some diurnal, some are terrestrial and some are arboreal, and of course, every variation in between. 

The sun sustains us and has done so throughout our history. It is with the intricacies of sunlight, and its knock on effects with regard to sustaining life that we need to spend some time if we can understand that terrestrial light does not just travel from the sun to the Earth. And then magically disappear. Then we are already halfway to designing fully functioning systems of bioactivity.

There are many things to take into consideration In regards to the evolutionary factors of light. We have to look at leaf or rock scatter light patterns, reflections back from the Earth itself, stone, water, and of course, limiting actions, such as predator avoidance, which in itself is a driving force behind 'solar utilization' and self regulation.

In truth, due to the progressive nature of Science and Technology, the theory of providing these parameters must remain fluid as we continue to learn more and more every day.

One of the key life support parameters of reptile care is of course, the correct provision of UVB as part of full-spectrum, plus UVB lighting. It is important that we do not blast irradiate or over-expose a species to a level/index of energy for which it does not use, nor has access to in the wild, as this could represent a chronic oversupply of this energy above and beyond it's own evolved level of protection from the sun.

We should, however, seek to provide the upper index or greatest quantity of solar energy that is common to a species in its habitat and to then allow that species to choose where and when to obtain the correct level for them which is in line with their biological needs. A well-thought-out depreciation into cool and shade as per the light and shade method will allow for the safe, self-regulation of your animals. 

We should never hang lamps low down into the vivarium, for instance, just to provide the animal with greater power: all this does is increase the risk of ocular infection; rather, it is better to fit lamps above the animal and to then use rocks, plants, and branches so that the species can climb upwards towards the lamp when and if it has need. 

It is vital that we, as forward-thinking keepers, realize that just because a deeply shaded area of Costa Rica may only provide an index of 0.25-0.5 at the forest floor, that this is not the 'total' amount of energy available to a species in its whole range. The theory of leaf scatter in itself will dictate that many thin shafts of light at greater indexes will push through the canopy and down into the understory towards the forest floor. We could, if it is easier, view them as tiny tanning salons provided for by nature and used by the animal to thrive. We must also keep in mind that almost all species can climb to some degree, although some may be better than others. This in itself will greatly increase the variation and quantity of index available to the species. Even an elevation of 5' from the forest floor will show a potential 3x increase in the available power and sheer footprint of light. 

In the height of summer we are exposed at midday to an index of around 5-10 in Canada. As a rule of thumb and for the most commonly kept deep forest or crepuscular species, we could provide an index of 1-3 depending on the need and behavior of a species. If we provide this level of energy for these leaf litter or crepuscular animals at a formal 'basking' zone, we will not go far wrong. This is both safe and measurable as the animal will be able to self-regulate into full exposure and away into total shade, and of course, can utilize the myraid of subtle index changes in between. 

Everything that we add into the lives of our pets should be safe, and it must be measurable or we should not seek to provide for it.

In an arid terrain, the sun is reflected onto the localized environment in a myraid of angles and off of most things that it encounters. This is the process that allows the effective transference of light and its energy (UV-IR) back off of the floor and rocks and into porous rocks and burrow mouths were some species will rest away from the searing heat and predation. This is a prime example of how a crepuscular species from arid/scrubland terrain can still benefit in full from both heat, being infrared and UVA-B. We call this "rock scatter illumination".

The sun in a tropical terrain is absorbed and reflected by water, leaves, and rocks in the forest/jungle habitats of the world. An arboreal species will benefit from exposure to direct sunlight from the top-down, but they would also be benefiting from light as it bounces around the canopy and down into the understory and further still towards the forest floor. Again, nocturnes that maybe found asleep by day and crepuscular species that are more active in lower light levels will still be able to benefit from this broad scatter of light as it travels at many angles through a forest. We call this "leaf scatter illumination".

Both "rock" and "leaf" scatter illumination have an active and vital role in the health and well being of all species, irrespective of their position in the ecosystem. 


If we, as keepers, can realize the sunlight does not just travel down from the sun in straight lines and hit the back and the head of a species or then magically disappear, we will start to truly understand the actions and limitations of light projections for any given species. Light, in its 'full spectrum' bounces around almost eternally under the atmosphere and around every other item that it encounters (rock, water, leaves, soil, ice, etc.), decreasing in power very slowly but infiltrating every nook and cranny or gap in the forest, desert, or Savannah; this is how the thinner skinned/crepuscular species are able to obtain this essential solar energy and make full use of the D3 cycle in the wild, even when not 'openly full body basking'. 

Why expose the whole body when you can develop a thinner more light-penetrating skin and simply expose a leg or a foot and come out fully in safer lower light times? Openly basking for many species simply increases the risk of predation. It would make evolutionary sense for a species to hide away in rocks and borrows or to stay hidden on the sides of trees while still being able to benefit from a percentage of this reflected sunlight. 

We can see how this infrared or heat is not only stored in part by rocks and high density materials, but also is reflected back into the habitat. Heat is extremely vital to the process of digestion and gastrointestinal transit, and how many cases of captive impaction can be attributed not only to a poor choice of substrate, but also to a poor or inadequate hydration and poorly appropriated heat. This natural process of heat being stored and reflected not only helps to heat and to regulate the core temperature of an ectothermic species, but also becomes an aid to its own core biological processes including internal organ function and digestion.

Light is energy and is vital for survival. The opposite of this provision of light and energy from light is, of course, darkness. So if a species has adapted/evolved to utilize light in all of its terrestrial wavelengths - will it have developed a use for a lack of light? 

The answer to this question of course is an emphatic, yes, in fact and in very real sense, the provision of darkness is just as important to the core biological cycles of reptiles (most life forms) as periods of natural sunlight is. Even if we forget for a moment those very truly, rare nocturnal species, or even those more common crepuscular animals, darkness is a time in which the core biological processes of a reptile (animal and plants) starts to allow the exact and effective assimilation of food and the utilization of the vitamins and minerals that have been collected during the more active period. Darkness is vital to maintaining the D3 cycle as a whole and ensuring its continued potency. 

Rest is vital. Maintaining a system in which light is provided for all through the night, even in quite small amounts, can not only interfere with an animal's biological cycles but can have a negative impact upon core brain function and even reproduction. Therefore, we must be sure of the correct provision of darkness alongside light. 

We should also place great importance on the provision of water through humidity in the early morning and, of course, evening/leading into the night. A light spray down just before an animal settles down for the night could make the difference between adequate hydration and excellent hydration. Even in the most arid regions, air humidity can go up surprisingly in the evening and morning, or be obtained underground in the burrows as the animal rests.

Light and its calculated omission, of course, can also be used to replicate seasonality, both in terms of an increase of food and light, leading to growth and reproduction, and its decrease leading to brumation in those species that require it! This is well-known in farming, where light levels are used to lengthen breeding cycles or otherwise increase yield in poultry. To boost the efficacy of our care programs and light provision systems, we must ensure that we view this provision of total darkness as just as important as providing light

Maintaining wildlife circadian rhythms at all times is not a luxury or optional extra for keepers in deciding whether to implement. They are Indeed part of the developed state of the species that we keep; as such, we must view the correct provision of these rhythms as core to our animals biological needs. 

Source: Bio-Activity and the Theory of Wild Re-Creation by John Courteney-Smith MRS

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