Understanding Reptile Vision, Part 1: Understanding Sight – October 2013

By Jennifer Greene

Hopefully, you have at least a basic understanding of how sight works.  In case you don’t, simply speaking the way humans perceive the world is through reflected light on objects around us.  For the majority of vertebrates, this is how sight works.  Light from the sun, a light bulb, moonlight, etc is reflected off of objects around us, and our eyes take in that light and send signals up to our brain indicating what it is we’ve seen. There’s different wavelengths of light – which most of you already know.  There’s visible light, which is the colors we see as humans, and then there’s wavelengths like UVA, UVB, UVC, and so on.  There’s also infrared light – which is, essentially, the same as heat.

Infrared, visible light, the UVB spectrum, these are a small portion of the BIG range of wavelengths that the sun and various light/energy sources can emit.  As far as we’re concerned, though, those are the relevant wavelengths for us to pay attention to.

The cells that send the signals up to our brain each fire when they encounter the type of light they’re designed to perceive, so your sight is only as good as the number of cells in your eyes.  And from there, your sight is only as good as the number of cells designed to pick up the various types of light out there.

The common way for vertebrates to see is through the use of two types of sight cells – rods and cones.  Rods simply pick up light, period, and fire when visible light hits them.  Cones pick up different colors of light, and there are various types of cones for the various colors or wavelengths of visible light out there.  In low light situations, rods work best, as they will just fire if there is light – so all of your rod cells are going to work to detect light when there isn’t much there.  Cone cells only fire when they are triggered by the specific type of light they’re designed to pick up – so they are not as effective as rod cells in low light, as there is often not enough reflected light of a specific color to make them fire.

This is extremely simplified; vision and lighting are complicated topics, and if you’d like to research it more, I highly recommend it.

As a result of the way the cells work, it is common and expected for most nocturnal species to have large numbers of rod cells in their eyes, allowing them to pick up even tiny amounts of reflected light at night and giving them excellent night vision.  Some owls, for example, have night vision up to 100 times better than what we can see – and this is due to the large number of rods in their eyes.

When it comes to daytime vision and cone cells, though, that’s where sight can get really interesting.  Different animal groups have different types of cones, and the way the cones work can vary immensely from animal type to animal type.

In mammals, it is common for them to only have 2 types of cones.  They are usually blind to the difference between the colors of red and green, a color range humans can detect because we have 3 types of cones.  Human color detection is better than most mammals, but it can only be called “better” in that range of comparison.  When you start to look at other vertebrates, the limits of our own sight become much more obvious.

Birds and many tropical fish can see into the Ultraviolet, or UV range, giving them the ability to perceive colors we can’t even comprehend.  Can you imagine a new color that has never existed before?  That’s a color that birds and many fish see all the time!

In that same group of exceptional sight, many reptiles have at least 4 types of cone cells, with some having 5.  This means they can perceive color even better than we can in most cases, and for species with the best color perception, they can see a range of colors that even birds and fish can’t.

This is definitely a generalization, and is not meant to imply that reptiles can all see with clarity and distance that we can – but they can perceive a wider range of colors than our senses can, and this should be considered when maintaining captive collections.

Obviously, not all reptiles require full spectrum lighting, or even much in the way of specialized lighting.  Commercialized breeding of several species has shown that specialized lighting is not necessary for the maintenance of some species, and this video and article series is not intended to dispute that.  Rather, this is a look at how reptiles perceive their world, and how we as keepers can better modify our lighting and cage setup to reflect the natural conditions our reptiles are likely to experience.  For the single pet reptile or for dedicated enthusiasts determined to closely replicate nature as best they’re able, information on reptile sight is just one aspect of husbandry to consider.

The Basking Spot: Powersun Lightbulbs – August 2013

Powersun Bulbs

by Jennifer Greene

I am often asked what bulb I recommend for various pet reptiles, especially for those that require both heat and full spectrum UVB lighting.  There are several options for providing the needed heat for your diurnal (daytime) pet reptile, as well as the UVB needed for proper vitamin D3 and calcium absorption.  My personal favorite method for providing heat, visible light, and UVB wavelengths of light is to use a mercury vapor bulb – in particular, the ZooMed Powersun Bulb.

The Powersun emits substantial amounts of both UVB and heat, making it ideal for desert dwelling reptiles or for species that prefer to bask at high temperatures.  It also allows yourreptiles to behave in a more natural fashion; the bright, white light that is making them warm is also what is emitting all the UV, similar to sunlight.  Artificial lighting is nowhere close to the range of light that the sun emits, but by providing intense heat and UVB in one place, you do allow your pet to seek out the conditions it would in the wild.  To metabolize D3 in the wild,reptiles need to be a certain temperature, while also receiving exposure to UVB.  This is true for most animals, including humans.  “Most vertebrates can either absorb vitamin D from the diet or synthesize it in the skin from 7-dehydrocholesterol using energy from ultraviolet (UV) light of certain wavelengths (290–315 nm) in a temperature-dependent reaction.” (merckmanuals.com)  The importance of properly heating your reptile, in addition to providing adequate UVB and supplementation, suddenly becomes much clearer!

For your pet reptile to properly utilize vitamin D3, then, it needs to be warm enough while it is digesting its meal and absorbing that all-important calcium (as well as other vital nutrients).  The reason the PowerSun is one of my favorite bulbs of all time becomes clear when you realize that in order to bask, your bearded dragon, blue tongue, lacerta, or other basking pet is not only getting the temperatures it needs under the light, but UVB as well, all at the time when it is actively seeking it out.

Blue Tongue Skink basking under a 100 watt Powersun Bulb

PowerSun bulbs come with a year-long warranty from ZooMed, and when used correctly, have a lifespan much longer than that.  I would suggest switching out your bulbs for optimal UVB output every 10 to 12 months.  I prefer to use a UVB meter to check UVB output on older bulbs, and often use older bulbs on cages where UVB is less important or where lower amounts of UVB are even preferred (my Frilled Dragons, for example, did much better under older bulbs that emitted lower amounts of UVB than new bulbs did).

To get the longest life from your bulb, make sure to read and follow the instructions that come with it.  These bulbs do best mounted vertically, straight up and down, and will last the longest if they are not jostled or moved frequently.  They are self-ballasted, and can be screwed into any regular light fixture.  However, it highly recommended to use a deep dome or 10” dome light fixture to allow for proper air flow around the bulb, both to prevent overheating and to keep the bulb from protruding out of the bottom of the fixture.  As a safety feature, these bulbs turn off automatically when they reach a certain temperature, or when heavily jostled or knocked over.  Once turned off, they require a cool down period before they can turn on again, so if your bulb does not immediately turn back on, give it 5 to 10 minutes and then try again.

We use PowerSun bulbs in our stores on our chameleon cages

Lastly, these bulbs are big, hot lightbulbs.  I only recommend them for larger enclosures; the smallest being an 18” x 18” x 24” front opening terrarium, or a 36” x 12” x 12” (or similar footprint) glass cage.  Keep in mind that in shorter enclosures, your pet cannot bask further away from the light if it wants, and in shorter cages the PowerSun may not always be the most suitable bulb.  Like all bulbs that produce heat, the PowerSun does naturally dry out enclosures it is used on, so for young animals or tropical species, extra attention should be paid to the humidity within the enclosure.  It is alright if it dry directly under the light if the rest of the enclosure is able to maintain humidity, or if a humid hide is provided.

Works Cited

Nutrition in Reptiles,  retrieved July 20th, 2013 from http://www.merckmanuals.com/vet/management_and_nutrition/nutrition_exotic_and_zoo_animals/nutrition_in_reptiles.html