Key concepts
Physics
Light
Reflection
Visibility
Introduction
Being outside in the evening can be relaxing as well as exciting and fun, but it can also be dangerous—especially if you are around roads. At dawn, dusk and during the night, it is difficult for drivers to see pedestrians. But do you think the types of clothes worn could make a difference in how visible pedestrians are to drivers? You probably know that camouflage makes you blend into the background. So, would wearing regular, noncamouflage materials be enough to make you more visible at night? Or would you choose to wear bright colors, fluorescent colors—or clothes with retro-reflective strips? This science activity will help you find out!
Background
Humans “see” when light that reflects off of objects reaches our eyes. Some colors send more light back so we see them better. For example, brightly colored objects reflect more light than dark-colored objects do. Fluorescent objects send out visible light when high-energy light shines onto them. Retro-reflective material—often referred to as reflective material, used on road signs and some safety gear, for example—bounces back almost all of the light that shines onto it.
At night, there is little light available to bounce off of objects. Typical nighttime light sources (headlights or street lights) rarely contain high-energy light, the type that makes fluorescent objects so bright in daylight.
In this science activity you will put three different “colors” (bright, fluorescent and retro-reflective) to the test. Which one do you think will increase visibility most in poor light conditions?
Materials
- At least two grown-up assistants—one to work with you as an observer (“driver”) and one to test out the different colors in the dark and play the role of a pedestrian.
- Black or dark clothing to cover most of the body of your adult tester
- Brightly-colored garment or item for your adult tester
- Fluorescent garment or item for your adult tester
- Reflector or item equipped with retro-reflective tape for your adult tester
- Two or more flashlights, including one that is very bright (The more powerful your flashlight, the better! It is meant to mimic a car headlight.)
- An open space with little or no lighting after dark where it will be safe to test the clothing at night
Preparation
- Whenever you are out after dark, observe what you can see, and what is hidden until it is near you. Use these observations to make a hypothesis of which “color” will most increase the visibility of a pedestrian. Will one “color” be way more visible from a distance? If so, why do you think this will be the case?
- Before you go out after dark to perform the test ask your test assistant(s) to dress in black or a dark color. Take the three items or garments that the test assistant(s) will use and at least two flashlights with you to the test place.
Procedure
- Have your observer (“driver”) assistant(s) hold the brightest flashlight; stay alongside them to help rate the visibility of the test assistant.
- Have your test “pedestrian” assistant(s) take a flashlight and the three different “colors” of clothing and safely walk out to about 30 meters straight ahead of the observer's flashlight—or until they are no longer very visible in their dark clothing. Once they arrive at a good distance for testing, have them flash a short on/off flashlight signal to alert the observer that it is time to rate the visibility.
- Now work with the observer to rate this “color” on a scale of 0 (not visible) to 10 (highly visible), imagining that you are in a car, and the flashlight is the headlight. Then signal back (again, a short off/on flashlight light signal) when done.
- The assistant can then take out (and/or put on) the brightly colored item and signal it is time to rate the visibility of that “color.”
- Rate the visibility with the observer. Were you surprised by this result? Now use your flashlight to signal back for the test assistant to try a different color—this time the fluorescent one.
- Repeat the process again and then, finally with the retro-reflective item.
- Is the difference in visibility of the different colors small, medium or large? Can you find a reason why a color increases visibility at night?
- Was your expectation correct? Are you surprised by the results? Does this change what you might wear as a pedestrian at night or in low-light conditions?
- Extra: Have your assistants switch roles—or enlist additional observers. Compare the ratings of the different observers. Do all agree that specific “colors” are more visible than others? Do they agree on which “colors” are most visible?
- Extra: In this test you rated the visibility of pedestrians about 30 meters away. Do you expect the results to be the same at shorter or farther distances? Perform a new test to find out!
- Extra: Think about what else a pedestrian could do to increase his or her visibility at night. Can you test these solutions in a similar way and compare these results with the ones you obtained in this activity? Did it increase visibility more, way more or less?
- Extra: Do you think pedestrians can accurately estimate how visible they are at night? To find out, ask people if they think a driver in a car can see them if they are dressed in the specific colors you tested. Compare their estimates with the test results you obtained.
- Extra: This test was performed at night in darkness. How do you think results would change under low-light conditions, such as dawn or dusk? How would you design such a test?
Observations and results
Did you notice how much the retro-reflective materials aid visibility in the test circumstances?
Although more light bounces off bright colors than it does off dark colors, the difference is not enough to make a pedestrian visible at night from a car with headlights on. Putting on a fluorescent-colored item might help a little, as fluorescent colors send out visible light when high-energy light shines on them. Streetlights and car headlights, however, usually do not produce much high-energy light; the small amount they do shine slightly increases the visibility, which might have made the pedestrian faintly visible in your test. This visibility was probably tiny compared with that of a pedestrian equipped with retro-reflectors. Reflectors are very efficient at reflecting the light back and into your eyes, and can significantly improve visibility at night.
As you decrease the distance between the car and the pedestrian, the visibility of each of the colors increases. Still, at any distance, the retro-reflective material wins the visibility contest.
Most pedestrians overestimate their visibility on the road after dark sets in. They often correctly indicate retro-reflective clothing increases their visibility but underestimate its effectiveness.
More to explore
Retroflectors, from ScienceBlogs
How to Make and Use Retroreflectors, from Make:
Colored Shadows, from Scientific American
Now you See It, Now Your Don't: A Chromatic Adaptation Project, from Science Buddies
Science Activity for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies
