The band Guess Who wrote the lyric ‘colored lights can hypnotize’ for their song American Woman. When writing those lyrics, I am sure they never intended them to refer to the world of herpetoculture. They may have been referring to some type of mind altering substance but they weren’t referring to reptiles and color vision. Moving onto the subject at hand there is an inordinate amount of reptile owners who for whatever reason believe that colored lights are good for reptile night heating. This belief is no doubt due in part to the advertising on the boxes of these colored bulbs.I too am guilty of recommending these colored bulbs when I worked the retail sector of the reptile world. Not making excuses for myself; at the time we had no other information to go on. The reptile industry of herpetoculture & the science of herpetology don’t always communicate which leads to many numerous misnomers and misinformation being given out to the public at large. The debate of who’s at fault is for another piece which would talk about the Ivory Tower and those too lazy to climb it.
In 2004 it was shown that nocturnal geckos were not only capable of acute vision in dim light but that they use the cones of their eyes for color vision in dim light. The same paper stated that while geckos had lost the red sensitive cone and oil droplets which would allow them to discern the color red, they still perceived not only ultraviolet light which is beyond human perception, they also see blue and green light. The two authors also suggested that the gecko eye lenses are probably multifocal which enhances the spatial resolution of their color vision creating well focused images on the retina.
I am sure that with the above points we can agree that any light, colored or not, will in fact disturb the normal circadian rhythm also called the sleep wake cycle. This is particularly true if we take into account that the geckos nocturnal as they might be are also seeing into the ultraviolet spectrum so therefore any light placed around or on the enclosure would be indeed visible . Within this same paper it is said “most diurnal vertebrates have cone-dominated retina with few rods and lizards have gone to the extreme: their retinae only cones (Walls 1942) and provide them with excellent colour vision (Wagner 1932).” Further studies done in lizard vision bear out results that many if not all lizards possess color vision of some type whether it be tetrachromatic or dichromatic. The fact remains that they are perceiving light and many of them seeing into the ultraviolet spectrum. Again from this we can infer that any light can and is seen by lizards.
Before moving on to the snakes here is something else to consider. Every field herper I know of sees a decrease in reptile activity during the full moon. Many of us reason this is due to predation exposure. Thus meaning on nights of the full moon that predation risk is far higher than those without a full moon. To my knowledge the luminosity (actually a reflection of sunlight as the moon doesn’t have its own light source) of the moon and its potential effects on reptile predation have yet to be examined and this may be an interesting paper for future research.
Ophidians or snakes are said to have evolved from lizards some millions of years ago. So it is understood that just as we as human primates inherit certain characteristics from our families so do all animals inherit things from the ones that came before them. In two different studies it is found that one of the least evolved snakes Python regius has ultraviolet (affiliate link) sensitive sight in which one paper posits that this may be used to track the visually ultraviolet reflective urine of their chosen rodent prey. Even further it is said that Python regius is dichromatic and may also have the potential for being trichromatic meaning that it sees three colors instead of being effectively color blind as most people presume. If the lowest evolved snake has such sensitive vision and with it being known that the most highly evolved snakes Viperidae do have some color vision as well as the ultraviolet light sensitivity seen in lower snakes; I would infer that all squamates have not only dichromatic vision but that potentially all of them have an acuity to sense ultraviolet light.
Understanding that, let’s now look at something obvious. The visual spectrum that humans can see is between 400nm-700nm. Ultraviolet light which humans cannot see is between 320nm-100nm. We now understand that reptiles see better than previously perceived (pun intended) so let me ask you this? Can you see the light emitted by that colored bulb? What makes you think that the reptile which has more acute vision than you cannot?
To the reptile that can see into the ultraviolet spectrum I infer that it would be very bright. Therefore, when we are attempting to heat our reptiles at night while not disturbing them by using colored bulbs it turns out that we are indeed disturbing the circadian rhythm. It has been shown that every living thing has a circadian rhythm which they experience and if you disrupt that rhythm then behavioral changes can and often do occur to compensate for the alterations.
I have personally witnessed alterations in behavior within a week or so of changing the red incandescent bulbs on my bearded dragon Pogona vitticeps for a non-light emitting ceramic heater (affiliate link) of appropriate size. He became more active during the day and began feeding better than when the red incandescent was used. No formal studies have been conducted on the circadian rhythms of squamates to my knowledge but I do think we are capable of inferring some basic tenets of sleep deprivation or the interruption of normal circadian cycles. As far as a nocturnal species is concerned as I stated above I would say there would be a higher stress load on such a reptile when being exposed to what must be an excessively bright light due to the natural make up of their vision.
In closing please do yourself and your reptile pet a favor and buy only ceramic heating elements that are not light emitting to keep them warm at night and if necessary by an under tank heater to supplement the ceramic heating element. If you want to watch your pet’s behavior at night buy some night vision goggles. Here is a link to a cheaper pair which is an affiliate link if you’re serious about stalking nocturnal reptiles.
Nocturnal colour vision in geckos Lina S. V. Roth and Almut Kelber The Royal Society Biology Letters
The Photoreceptors and visual pigments in the retina of boid snake, the ball python (Python regius) A.J. Sillman, J.K. Carver and E.R. Loew