We took our first look at measuring light sources a while back as our first step toward understanding the differences in automotive headlight options. In this article, we’ll provide a practical demonstration of why it’s crucial for the lighting on your car, truck, motorcycle, ATV or side-by-side to emit light that covers the entire color spectrum evenly.
Light Sources and the Human Body
Light waves work similarly to sound waves in that both our eyes and ears are sensitive to a specific range of frequencies. For sound, most adults can hear from 20 Hz to around 15 kHz and see light in the range of 400 to 790 THz (terahertz). Sounds above 15 or 20 kHz are imperceivable as our ears don’t detect those signals and send the information to our brain. Likewise, energy below 400 THz (which is infrared) isn’t seen by our eyes but can be felt as heat on our skin. Frequencies above 790 THz, which is ultraviolet light, are also invisible to our eyes but can cause skin damage in the form of sunburn. Butterflies, some birds, reindeer and sockeye salmon can see ultraviolet light. At the other end of the spectrum, some snakes, fish and frogs can see infrared light.
How Our Eyes Perceive Objects
If you shine a white light at an object, that object reflects specific colors to our eyes. Those reflected colors match the color of the object. So, if you shine white light on a blue car, then blue light wavelengths are reflected to your eyes. The same goes for the yellow lane markings on the road and green grass on the boulevard or median.
Let’s put this concept into a set of simple rules. First, we’ll consider the sun on a cloudless day as a near-perfect light source. The sun emits light energy that’s very evenly distributed through the color spectrum.
If you look at the spectrographic analysis of the light from the sun shown above, you can see that from light blue through to light red, the spectral density is fairly similar.
What if Color Is Missing from a Light Source?
We’ll set up a demonstration to show what happens when a specific color of light is missing from a light source and how that affects the way we perceive objects. We have a set of RGB LED strip lights set 18 inches away from a selection of Hot Wheels cars for this demonstration. We can use the smartphone app to choose which of the LEDs are on. First, we’ll take pictures of the cars with the camera flash, then with just the red, then the green, then the blue LEDs on so you can see which cars light up and which don’t.
If you compare the photo of the cars illuminated with the flash to those with only single colors of lights, we can see that some vehicles are quite dark. In the image with the red LEDs, the green and blue cars remain dark. In the image with the green lighting, the red and blue cars are dark. It should now come as no surprise that the red and green cars look dark in the image with the blue lighting.
Going back to our rules concept, if our light source doesn’t offer light energy that matches the color of an object, we won’t perceive that object as being illuminated.
Just for references, we’ll include spectrographic analysis of the red, green and blue LEDs so you can see how narrowly focussed their light output is.
We are getting close to a point where we have enough information and understanding of how light works to analyze and understand the color content of different headlight bulb options. So please don’t fret; we’ll get to that information soon! In the meantime, if your headlights aren’t bright enough, drop by your local specialty mobile enhancement retailer and ask them about options to upgrade the lighting system on your car or truck.