CYSF

Presentation

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Hypothesis

If you shine a light source into an animal’s eyes in the dark, then different species’ eyes will reflect a different amount of light and be a different colour.

Research

Introduction

We decided to team up on a science project and were looking for a scientific question that would be related to animals. The idea for the project came, when Adelyne saw a fox run across her driveway in the dark and the car’s headlights reflected on the fox’s eyes making them glow in the dark. Adelyne also noticed that her dog’s eyes glow in the dark, but they were different colour than the fox’s eyes. This observation gave us an idea for the science fair.

For our science fair project, we want to do an experiment to understand why animals’ eyes glow in the dark. We want to see if different species’ eyes glow more than others and find out if they glow in different colours.

Scientific Question

Why do animal’s eyes glow in the dark?

Do different species’ eyes glow more than others and do they glow in different colours?

Hypothesis

If you shine a light source into an animal’s eyes in the dark, then different species’ eyes will reflect a different amount of light and be a different colour.

Variables

Manipulated (Independent) variable

The manipulated variable for this experiment is animal species.

Responding (Dependent) variable

The responding variable is the amount of glow (reflection and colour observed cming from the animals’ eyes.

Controlled Variables

Controlled variables for this experiment include the light source, the distance we stand away from the animal when we shine the light in their eyes, the same amount of time we shine the light source, the same way we measure the eye glow, the same dark conditions used to test the animals, only mammal species will be tested.

Show The Glow Research Report

To define our research question, we asked several other questions, which are listed below. We did research and read several scientific articles and book chapters that explained us the structure of the eye and possible reasons why the eye glow might benefit different mammals. Our research also helped us decide which animals’ eyes to study and how to design our experiment. Read on to learn what we found out!

Subtopics

Why do animals’ eyes glow?

How do animals’ eyes glow?

Which animal’s eyes glow the most?

What part of animals’ eyes glow?

How does it affect their lives?

What animals should we test?

Do different animals’ eyes glow different colours?

Do the same species eyes glow the same amount?

If animals are nocturnal would their eyes glow more?

How are mammals’ eyes structured?

What are the benefits of their eyes glowing?

What are the best methods for researching this topic?

What is the relevance of our findings?

The Why and The How

We started with our big questions: why do animals’ eyes glow? We also wanted to know how their eyes glow and do their eyes glow more if they are nocturnal? How does it affect their lives? And what are the benefits of their eyes glowing?

We found out that nocturnal animals’ eyes do indeed glow more as it has several benefits for them. The biggest benefit is that they can see better in the dark. Cats rely on their vision to help them catch prey and have excellent vision, which helps them to operate in various environments under different light conditions. A domestic cat’s vision sharpness however is not as high as wild cats’ vision sharpness. That is because cat’s eye size determines the amount of light captured by the eye. The relatively large size of their eyes improves light capture to produce a brighter retinal image. Through evolutionary processes cats’ eye structure has adapted for nocturnal vision supporting cats’ nocturnal life. A tapetum lucidum of a cat is made of cells that reflect light back to the retina. (Corsi et al., 2022).

Animals that have eyes that glow very bright in the dark have more rods in their retinas. Animals that can see well in the dark cannot see colour well. Eyeshine helps animals hunt because they can see better in the dark. Many mammals have glowing eyes, but spiders, alligators and frogs also have reflective eyes. Animal eyes can glow different colours depending on the species, brightness of the light and how the light hits the eye. (Hiller, 1983).

The Tapetum Lucidum

We needed to know in more detail how mammals’ eyes are structured and which part of the eye glows. The sources explained that the eye has the following structure:

Image: Nocturnal Animals and Night Vision, 2004.

Eyes have rods and cones. Cones help you see in the daylight and detect colour. Rods work in dim light and help you see shape and motion. Nocturnal animals have lots of rods giving good night vision. Humans have more cones so can see better in the daytime than at night. (Nocturnal Animals and Night Vision, 2004).

We learned that the part responsible for the eye glow is the Tapetum Lucidum (Tapetum). (Ribi, 1980). It is made of reflective cells at the back of the eyeball that act like a mirror bouncing light back to the receptor cells a second time. This is why we see animals’ eyes glow when a light shines at them. (Fergus, 2005).

Image: Dr. Robin Peterson, The Horse, December 6, 2020.

We were invited to Grade 7/8 science laboratory that did dissections of eyeballs. Mr. Churchill demonstrated how a horse eye dissection is done, and we were then able to dissect a sheep eye and a cow eye. Please read our separate Dissection Report to find out how it was done and what we found out!

Which Animals Should We Test and How?

Based on our initial research we decided to concentrate on mammals and especially those that we have access to as they are our pets and comfortable with us doing an experiment with them. We would not be able to safely test the eye glow of an alligator even though it is the brightest! The second classification was to divide our test animals to nocturnal and diurnal. Our test animals are a cat, a dog, a bunny, and a horse. Out of these animals, cats are nocturnal and the others diurnal. But which animal’s eyes glow the most? And do different animals’ eyes glow different colours?

We designed an experiment and consulted a veterinarian to confirm that our experiment design would be effective and not harm the animals. She pointed out that we would need to have an animal handler that is comfortable with the animal tested and this was a good reminder as we would like the animal to be calm and not be stressed by the test. She also said that we should not use animals with blue eyes to compare the glow between species because blue eyed animals are missing pigment in their tapeta, and it will act differently. She recommended that we use a camera flash as the light source for our experiment and record the experiment with another camera in slow motion to better see the light that reflects from each animals’ eyes. (Fick, 2025).

We also learned that one way to measure light is to use lux as the measurement unit. A lux describes how much light falls on a certain area. Smartphones have built-in light sensors to measure lux. (Finio, 2019). Please read on to find out how we did our experiment and what the results are!

Show The Glow Conclusions

Based on our research, dissections of the eyeballs, and experiments to measure the eye glow we conclude that several animals’ eyes glow in the dark but not all animals have glowing eyes. The eye glow is caused by the Tapetum Lucidum, a part of the eye that reflects the light in some mammals’ eyes. The cat’s eyes glow the most because it is a nocturnal animal. Its eyes glow in a yellow/white colour, the dog’s eyes glow in green/white colour, the bunny’s eyes in the colour red and the horse’s in a blue/white colour. The Tapetum Lucidum of the horse, the sheep, and the cow are all a bluish colour. The benefits of the eye glow include being able to see better in the dark.

Further Questions

After doing our experiment we would really like to see how predators’ eyes shine! We know they have bigger eyes, but would the shine be much stronger when measured the way we measured the eye glow of a domestic cat?

Real World Application

Now that you understand this cool phenomenon you know how the fox you were just about to crash into saved itself with its unique eye glow. Or you might even study your own pet’s eye glow using our experiment design.

Show The Glow Bibliography

“Adaptation.” Britannica Kids, kids.britannica.com/kids/article/adaptation/352704. Accessed 14 January 2025.

Chamary, JV. “Animal Vision: How Do Animals See?”. Discover wildlife, BBC Wildlife Magazine, 2023, discoverwildlife.com/animal-facts/animal-vision-how-do-animals-see. Accessed 6 January 2025.

Corsi, Francesca et al. “Ophthalmology of Felidae: Cats”. Wild and Exotic Animal Ophthalmology, Volume 2: Mammals. eds. Fabiano Montiani-Ferreira, Bret A. Moore & Gil Ben-Shlomo. Springer Nature Switzerland, 2022, 155-180. doi.org/10.1007/978-3-030-81273-7. Accessed 12 January 2025.

Fergus, Charles. “Bears”. Stackpole Books, 2005, books.google.ca/books?id=ejIQ7EHhMQQC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false. Accessed 6 January 2025.

Fick, Laura. Consultation with Veterinarian. Bragg Creek Veterinary Clinic, 2025, Bragg Creek.

info@braggcreekvet.ca. 15 January 2025.

Finio, Ben. “Science with a Smartphone: Measure Light with Lux.” Scientific American, 3 October 2019, www.scientificamerican.com/article/science-with-a-smartphone-measure-light-with-lux/. Accessed 14 January 2025.

Hausheer, Justine E. “When Mammals Glow in the Dark”. Cool Green Science, The Nature

Conservancy, 2021, blog.nature.org/2021/04/05/when-mammals-glow-in-the-dark/. Accessed

12 November 2025.

Hiller, Ilo. “Eyeshine.” Texas Parks and Wildlife Department, 1983, tpwd.texas.gov/publications/nonpwdpubs/young_naturalist/animals/eyeshine/index.phtml. Accessed 14 January 2025.

Hoglund, G. “Glow, Sensitivity Changes and Pigment Migration in the Compound Eye of Nocturnal Lepidoptera”. Life Sciences, 1963, No, 4, 275-280. https://www.sciencedirect.com/science/article/abs/pii/0024320563900109. Accessed 6 January 2025.

Kerr, Elizabeth. “Glow in the Dark: Bioluminescence in the Animal and Human World.” Charlotte Teachers Institute, 2020, https://charlotteteachers.org/. Accessed 12 January 2025.

Lesté-Lasserre, Christa. “Basic Equine Eye Anatomy.” The Horse, 2020. https://thehorse.com/195550/basic-equine-eye-anatomy/. Accessed 8 March 2025.

Nature-detectives. “Nocturnal Animals and Night Vision.” Boulder County, 2024, assets.bouldercounty.gov/wp-content/uploads/2017/03/nature-detectives-2004c.pdf. Accessed 8 January 2025.

Ribi, W. A. “The Phenomenon of Eye Glow.” Endeavour, 1980, New Series Volume 5, No 1.,

sciencedirect.com/science/article/abs/pii/0160932781900727. Accessed 6 January 2025.

“Top Ten Cool Ways that Animals See in the Dark.” Earth Ranger, 2014, earthrangers.com/EN/CA/top-10/top-ten-cool-ways-that-animals-see-in-the-dark/. Accessed 12 January 2025.

Vee, Samantha, et al. “The glow of the night: The tapetum lucidum as a co-adaptation for the inverted retina.” BioEssays, vol. 4, no. 20, 2022, onlinelibrary.wiley.com/doi/abs/10.1002/bies.202200003. Accessed 6 January 2025.

Walls, Gordon L. “The vertebrate eye and its adaptive radiation.” Cranbrook Institute of Science, 1942, biodiversitylibrary.org/page/6976169. Accessed 7 January 2025.

Acknowledgements

Dr. Laura Fick, Bragg Creek Veterinary Clinic

Lilly the bunny

Marmalade the cat

Mr. Churchill, grade 7/8 science teacher

Rowan the bunny owner

Snowa the dog

Wendy the horse owner

Willy the horse

Variables

Manipulated (Independent) Variable –The manipulated variable for this experiment is animal species.

Responding (Dependent) Variable – The responding variable is the amount of glow (reflection) and colour observed coming from the animals’ eyes.

Controlled Variables - Controlled variables for this experiment include the light source, the distance we stand away from the animal when we shine the light in their eyes, the same amount of time we shine the light source, the same way we measure the eye glow, the same dark conditions used to test the animals, only mammal species will be tested.

Procedure

Show The Glow Experiment Design

Gather the required material listed on the material list.
Assign roles in order to conduct the experiment.

One person will be the animal handler (note the animal handler may change for each animal, depending on who the animal is most comfortable with and who can handle each animal safely). Called the animal handler.
One person will operate the Smartphone light meter and record observations on the datasheet. Called the recorder.
One person will operate the Smartphone camera. Called the camera operator.

Put on headlamps, keeping them turned off.
Have the Smartphone camera fully charged and enable the flash. The same Smartphone camera will be used for the entire experiment.
Go to the dark location with the lights on (a walk-in closet with no windows was used).
The recorder opens the Light Meter app on the second Smartphone.
Turn lights off.
In dark conditions, the recorder takes a reading of the dark location prior to conducting the experiment, with the Light Meter app, using the light setting. This will ensure that the dark location is the same “darkness” for each trail and species.
Turn on headlamps to be able to see in the dark location.
The recorder records the Light Meter reading in lux units on the data sheet.
Bring the test animal into the dark location, taking care to make sure the animal is comfortable. Do not shine headlamps directly into the animals’ eyes. The animal handler will stay with each animal for the duration of the experiment.
Record test animal species on data sheet. The test species is the manipulated variable. A dog, cat, bunny and horse will be tested.
Using the meter stick, measure 50 cm from the animal‘s eyes.
Have the camera operator stand at the 50 cm mark from the test animal.
Have the recorder stand by the camera operator.
Prepare the light meter and direct it towards the test animals’ face.
Turn headlamps off.
The recorder will count to three out loud.
When the recorder says “three”, the camera operator will take a photo of the animal holding the camera towards the test animals’ eyes.
The recorder will watch the light meter during the camera flash and resulting “glow/reflection” seen in the animals’ eyes and note the lux value and eye colour.
Turn headlamps on.
The animal handler will reassure the test animal and give them a species’ specific treat.
The recorder will record observations - lux reading (equivalent to the amount of light reflected by the animals’ eyes or “glow” observed, percentage of eye glowing, consistency of eye glow colour and the eye colour.
If the test animal was comfortable with the experiment and is cooperative, the test will be conducted two more times, with each animal, for a total of three replicates by following steps 6-23.
Once three replicates are complete, the animal handler will remove the test animal from the dark location.
The experimental team will review the photos to confirm eye colour observed and discuss any additional observations.
The experimental team will prepare for the next test animal.
The experimental team will repeat steps 6-26 until all test animals have been tested.
As the horse could not be brought into the walk-in closet, the horse was tested outside in the paddock, in the dark. To ensure the same dark conditions were achieved, the light meter was used to measure the darkness, the test proceed only if the light meter read the same value as the walk-in closet.
Ensure that the experimental team keeps the same roles throughout the experiment, with the exception of the animal handler, to ensure consistent observations and actions.
Analyze collected data.
Discuss what modifications should be done if this experiment was repeated.

Show The Glow Experiment Setup

Materials

Dog, Cat, Horse, Bunny, Light source, Smartphone flash of camera, Tape measure (m), Dark location, Light meter app on Smartphone (Light Meter Luminosity Measure, WeBrain, Version 1.9), Animal treats specific to each test species, Pencil to record observations, Paper datasheet to record observations, 3 people, and 3 headlamps.

Show The Glow Observations

Table 1. Bunny Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Trail 1 - Bunny	Feb. 21/25	2:53 pm	3 Lux	Black	Red	3 Lux*	Triangle	50%	Stayed red	Scared but stayed still
Trail - 2 - Bunny	Feb. 21/25	2:54 pm	3 Lux	Black	Red	3 Lux*	Triangle	60%	Stayed red	Scared but stayed still
Trail 3 - Bunny	Feb. 21/25	2:55 pm	3 Lux	Black	Red	3 Lux*	Triangle	40%	Stayed red	Scared but stayed still

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Table 2. Cat Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Trail 1 - Cat	Feb. 21/25	2:04 pm	3 Lux	Orange	Yellow/white	3 Lux*	Oval	100%	Yellow/White	Hard -moved a lot
Trail 2 - Cat	Feb. 21/25	2:07 pm	3 Lux	Orange	Yellow/white	3 Lux*	Oval	95%	Changed greener	Hard -moved a lot
Trail 3- Cat	Feb. 21/25	2:08 pm	3 Lux	Orange	Yellow/white	3 Lux*	Oval	100%	Yellow	Hard -moved a lot

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Table 3. Dog Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Dog	Feb. 21/25	1:39 pm	3 Lux	Honey Brown	Green/White	3 Lux*	Circle	95%	Stayed green/white	Easy - treat motivated
Dog	Feb. 21/25	1:53 pm	3 Lux	Honey Brown	Green/White	3 Lux*	Circle	85%	Stayed green/white	Easy - treat motivated
Dog	Feb. 21/25	1:55 pm	3 Lux	Honey Brown	Green/White	3 Lux*	Circle	85%	Stayed green/white	Easy - treat motivated

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Table 4. Horse Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Horse	Feb. 21/25	9:06 pm	3 Lux	Dark Brown	Blue/white	3 Lux*	Sideways teardrop	75%	Stayed blue/white	Medium - moved
Horse	Feb. 21/25	9:06 pm	3 Lux	Dark Brown	Blue/white	3 Lux*	Sideways teardrop	75%	Stayed blue/white	Medium - moved
Horse	Feb. 21/25	9:09 pm	3 Lux	Dark Brown	Blue/white	3 Lux*	Sideways teardrop	75%	Stayed blue/white	Medium - moved

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Show The Glow Results

Figure 1 shows that the cat consistently had the highest percentage of the eye glow in each trail, followed by the dog and then the horse. The least percentage of eye glow was observed in the bunny.

The Smartphone light meter was not able to measure/pick-up the eye glow from the test animals’ eyes, despite research indicating this would be a good way to measure the glow or light coming from the animals’ eyes. Figure 2 indicates that the light meter measured 3 lux for every trail and each animal.

As the light meter could not measure the resulting eye glow, photos were examined of each trail and ranked according to most eye glow observed to least eye glow observed (1 most glow, 4 least glow observed). This ranking was used as a qualitative measurement to determine the amount of eye glow observed for each species (Figure 3). Rankings determined that the cat had the most eye glow and the bunny had the least eye glow. The dog was second followed by the horse in third place.

Table 5 shows the observed colour of each species' eye glow. Eye glow colour was different for each species tested and consistent with what research indicated the colour would be. The bunny was red, the cat was yellow/white, the dog was green/white, and the horse was blue/white (Table 5).

Figure 1. Percentage of Eye Glow Observed Glowing for Each Species.

Figure 2. Eye Glow Intensity Observed for Each Species.

Figure 3. Ranking of Eye Glow Intensity Observed for Each Species.

Table 5. Observed Animal Species Eye Glow Colour.

Animal Species	Eye Glow Colour (Trial 1)	Eye Glow Colour (Trial 2)	Eye Glow Colour (Trial 3)
Bunny	Red	Red	Red
Cat	Yellow/White	Yellow/White	Yellow/White
Dog	Green/White	Green/White	Green/White
Horse	Blue/White	Blue/White	Blue/White

Show the Glow Eye Dissection Report

Linnea asked for a permission to observe eye dissections performed by grade 7/8. We were invited to perform our own dissections of a cow eye and sheep eye.

Cow Eye

Experiment Description

The eyeball was covered in fat and muscles that had to be stretched and then cut. This process was repeated until we were left with a sideways oval that had no fat on it. The next process was to make a small puncture in the middle of the eye. When we punctured the eye water sprayed out of it. Next, we took out our scissors and cut on from the puncture until we were left with two separate halves. Inside of these two halves were all the different parts of the eye. These parts included the lens, pupil, iris, retina, optic lens and the tapetum lucidum (tapetum). The cow’s tapetum was a mixture of different shades of blue. When these processes were done, we took pictures of each of the parts to be a part of our trifold.

Observations

After the cow dissection was done and we did the sheep eyeball dissection we both realized that the sheep eye was way waterier than the cow’s eye.

Sheep Eye

Experiment Description

When we got the sheep eyeball it was covered in fat that e had to stretch and then peel. After taking off the fat we had to cut all the muscles leaving us with a circular eye. Next, we stabbed the eye with a scalpel. As we stabbed the eye water sprayed out from the inside of the eye. After we stabbed the eye, we used scissors to cut the eye in half by cutting on from the slit. We then ended up with two separate halves that revealed the inside parts of the eye. Then we took apart the pieces of the eye. These pieces are the lens, pupil, iris, retina, optic lens and the tapetum lucidum (tapetum). As we looked at the tapetum we saw that it had various shades of blue for its colour. The tapetum we realized was a very similar colour to the cow’s eye. We took pictures of each of these parts to display on our trifold.

Observation

We realized that the sheep eye was a lot smaller than the cow and horse eye.

Horse Eye

We also observed a dissection of a horse eye and the tapetum lucidum (tapetum) was very similar to the dissection we did with the cow and sheep eye. This horse’s tapetum was a colour of different shades of blue.

Samples

Observations

Show The Glow Observations

Table 1. Bunny Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Trail 1 - Bunny	Feb. 21/25	2:53 pm	3 Lux	Black	Red	3 Lux*	Triangle	50%	Stayed red	Scared but stayed still
Trail - 2 - Bunny	Feb. 21/25	2:54 pm	3 Lux	Black	Red	3 Lux*	Triangle	60%	Stayed red	Scared but stayed still
Trail 3 - Bunny	Feb. 21/25	2:55 pm	3 Lux	Black	Red	3 Lux*	Triangle	40%	Stayed red	Scared but stayed still

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Table 2. Cat Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Trail 1 - Cat	Feb. 21/25	2:04 pm	3 Lux	Orange	Yellow/white	3 Lux*	Oval	100%	Yellow/White	Hard -moved a lot
Trail 2 - Cat	Feb. 21/25	2:07 pm	3 Lux	Orange	Yellow/white	3 Lux*	Oval	95%	Changed greener	Hard -moved a lot
Trail 3- Cat	Feb. 21/25	2:08 pm	3 Lux	Orange	Yellow/white	3 Lux*	Oval	100%	Yellow	Hard -moved a lot

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Table 3. Dog Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Dog	Feb. 21/25	1:39 pm	3 Lux	Honey Brown	Green/White	3 Lux*	Circle	95%	Stayed green/white	Easy - treat motivated
Dog	Feb. 21/25	1:53 pm	3 Lux	Honey Brown	Green/White	3 Lux*	Circle	85%	Stayed green/white	Easy - treat motivated
Dog	Feb. 21/25	1:55 pm	3 Lux	Honey Brown	Green/White	3 Lux*	Circle	85%	Stayed green/white	Easy - treat motivated

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Table 4. Horse Results

Animal Type	Test Date	Time	Lux Meter Reading of dark test location (Lux)	Eye Colour in Daylight	Eye Shine Colour	Lux Meter Reading of Eye Shine (Lux)	Shape of Eye Shine	% of eye glowing (average of three trails)	Eye Shine Colour Consistency	Animal Cooperation
Horse	Feb. 21/25	9:06 pm	3 Lux	Dark Brown	Blue/white	3 Lux*	Sideways teardrop	75%	Stayed blue/white	Medium - moved
Horse	Feb. 21/25	9:06 pm	3 Lux	Dark Brown	Blue/white	3 Lux*	Sideways teardrop	75%	Stayed blue/white	Medium - moved
Horse	Feb. 21/25	9:09 pm	3 Lux	Dark Brown	Blue/white	3 Lux*	Sideways teardrop	75%	Stayed blue/white	Medium - moved

*Note: Smartphone Luxmeter was not able to measure/pick-up the eye glow from the test animals.

Show The Glow Results

Figure 1 shows that the cat consistently had the highest percentage of the eye glow in each trail, followed by the dog and then the horse. The least percentage of eye glow was observed in the bunny.

The Smartphone light meter was not able to measure/pick-up the eye glow from the test animals’ eyes, despite research indicating this would be a good way to measure the glow or light coming from the animals’ eyes. Figure 2 indicates that the light meter measured 3 lux for every trail and each animal.

As the light meter could not measure the resulting eye glow, photos were examined of each trail and ranked according to most eye glow observed to least eye glow observed (1 most glow, 4 least glow observed). This ranking was used as a qualitative measurement to determine the amount of eye glow observed for each species (Figure 3). Rankings determined that the cat had the most eye glow and the bunny had the least eye glow. The dog was second followed by the horse in third place.

Table 5 shows the observed colour of each species' eye glow. Eye glow colour was different for each species tested and consistent with what research indicated the colour would be. The bunny was red, the cat was yellow/white, the dog was green/white, and the horse was blue/white (Table 5).

Figure 1. Percentage of Eye Glow Observed Glowing for Each Species.

Figure 2. Eye Glow Intensity Observed for Each Species.

Figure 3. Ranking of Eye Glow Intensity Observed for Each Species.

Table 5. Observed Animal Species Eye Glow Colour.

Animal Species	Eye Glow Colour (Trial 1)	Eye Glow Colour (Trial 2)	Eye Glow Colour (Trial 3)
Bunny	Red	Red	Red
Cat	Yellow/White	Yellow/White	Yellow/White
Dog	Green/White	Green/White	Green/White
Horse	Blue/White	Blue/White	Blue/White

Show the Glow Eye Dissection Report

Linnea asked for a permission to observe eye dissections performed by grade 7/8. We were invited to perform our own dissections of a cow eye and sheep eye.

Cow Eye

Experiment Description

The eyeball was covered in fat and muscles that had to be stretched and then cut. This process was repeated until we were left with a sideways oval that had no fat on it. The next process was to make a small puncture in the middle of the eye. When we punctured the eye water sprayed out of it. Next, we took out our scissors and cut on from the puncture until we were left with two separate halves. Inside of these two halves were all the different parts of the eye. These parts included the lens, pupil, iris, retina, optic lens and the tapetum lucidum (tapetum). The cow’s tapetum was a mixture of different shades of blue. When these processes were done, we took pictures of each of the parts to be a part of our trifold.

Observations

After the cow dissection was done and we did the sheep eyeball dissection we both realized that the sheep eye was way waterier than the cow’s eye.

Sheep Eye

Experiment Description

When we got the sheep eyeball it was covered in fat that e had to stretch and then peel. After taking off the fat we had to cut all the muscles leaving us with a circular eye. Next, we stabbed the eye with a scalpel. As we stabbed the eye water sprayed out from the inside of the eye. After we stabbed the eye, we used scissors to cut the eye in half by cutting on from the slit. We then ended up with two separate halves that revealed the inside parts of the eye. Then we took apart the pieces of the eye. These pieces are the lens, pupil, iris, retina, optic lens and the tapetum lucidum (tapetum). As we looked at the tapetum we saw that it had various shades of blue for its colour. The tapetum we realized was a very similar colour to the cow’s eye. We took pictures of each of these parts to display on our trifold.

Observation

We realized that the sheep eye was a lot smaller than the cow and horse eye.

Horse Eye

We also observed a dissection of a horse eye and the tapetum lucidum (tapetum) was very similar to the dissection we did with the cow and sheep eye. This horse’s tapetum was a colour of different shades of blue.

Analysis

Show The Glow Results

Figure 1 shows that the cat consistently had the highest percentage of the eye glow in each trail, followed by the dog and then the horse. The least percentage of eye glow was observed in the bunny.

The Smartphone light meter was not able to measure/pick-up the eye glow from the test animals’ eyes, despite research indicating this would be a good way to measure the glow or light coming from the animals’ eyes. Figure 2 indicates that the light meter measured 3 lux for every trail and each animal.

As the light meter could not measure the resulting eye glow, photos were examined of each trail and ranked according to most eye glow observed to least eye glow observed (1 most glow, 4 least glow observed). This ranking was used as a qualitative measurement to determine the amount of eye glow observed for each species (Figure 3). Rankings determined that the cat had the most eye glow and the bunny had the least eye glow. The dog was second followed by the horse in third place.

Table 5 shows the observed colour of each species' eye glow. Eye glow colour was different for each species tested and consistent with what research indicated the colour would be. The bunny was red, the cat was yellow/white, the dog was green/white, and the horse was blue/white (Table 5).

Figure 1. Percentage of Eye Glow Observed Glowing for Each Species.

Figure 2. Eye Glow Intensity Observed for Each Species.

Figure 3. Ranking of Eye Glow Intensity Observed for Each Species.

Table 5. Observed Animal Species Eye Glow Colour.

Animal Species	Eye Glow Colour (Trial 1)	Eye Glow Colour (Trial 2)	Eye Glow Colour (Trial 3)
Bunny	Red	Red	Red
Cat	Yellow/White	Yellow/White	Yellow/White
Dog	Green/White	Green/White	Green/White
Horse	Blue/White	Blue/White	Blue/White

Conclusion

Based on our research, dissections of the eyeballs, and experiments to measure the eye glow we concluded that several animals’ eyes glow in the dark but not all animals have glowing eyes. The eye glow is caused by the Tapetum Lucidum, a part of the eye that reflects the light in some mammals’ eyes. The cat’s eyes glowed the most because it is a nocturnal animal. Its eyes glow in a yellow/white colour, the dog’s eyes glow in green/white colour, the bunny’s eyes in the colour red and the horse’s in a blue/white colour. The Tapetum Lucidum of the horse, the sheep and the cow are all a bluish colour. The benefits of the eye glow include being able to see better in the dark.

Application

Further Questions

After doing our experiment we would really like to see how predators’ eyes shine! We know they have bigger eyes, but would the shine be much stronger when measured the way we measured the eye glow of a domestic cat?

Real World Application

Now that you understand this cool phenomenon you know how the fox you were just about to crash into saved itself with its unique eye glow. Or you might even study your own pet’s eye glow using our experiment design.

Sources Of Error

We could have used a diferent LUX meter that would have been more sensitive.

We could expand the research project by measuring eye glow of more animals. We could not experiment with wild animals.

We could perform eye dissection of other animal's eyes.

Citations