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.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

When it comes to lighting the road in front of your car or truck at night, most enthusiasts focus on light intensity instead of headlight bulb color. It’s straightforward to see the difference between yellowish light produced by incandescent halogen bulbs and the white/blue output of HID or LED bulbs. The science behind these light sources is interestingly similar to what professional car audio technicians measure to calibrate a digital signal processor in your mobile audio system. If you’re intrigued, read on, and we’ll explain in detail.

How Light Works

There have been many detailed scientific dissertations on how light works. These papers explain the electron and sub-electron concepts that allow us to see objects. In short, light is made of photons. Photons are packets of electrons that have been released from atoms. These packets of photons have energy and momentum but have no mass. This means you can shine a light at an object to illuminate it, but the energy from the light source doesn’t make the object heavier.

If we excite a group of atoms, the negatively charged electrons that orbit the nucleus absorb that energy. As more energy is added to an atom, the electrons circle faster and farther away from the center. When the energy source (electricity or heat) is removed, the electrons snap back to their original orbit path but release that added energy in the form of photons. Under specific conditions, the photons that are released produce visible light. If you studied electrical theory in high school, you’d recognize this pattern as similar to how electricity works. The only difference is that electricity involves electrons jumping from one atom to another to transfer energy.

When the light photons escape from an atom, they can have varying energy levels depending on the electron’s position when it leaves the atom. You can think of this as the photons having a specific resonant frequency. As a result, different types of atoms release photons of different wavelengths. The result is differently colored light sources.

Light and Color

We know that light sources have different colors. An incandescent bulb gives off a very different kind of light than a fluorescent bulb, a gas-discharge arc lamp (high-intensity discharge or HID) or a light-emitting diode (LED). Some light sources appear yellow, while others are white or blue. How these light sources illuminate objects can make them look very different.

Let’s take a giant step sideways. You’ve seen plenty of rainbows, but do you know what turns the supposedly white light from the sun into a color pattern that shifts from violet through to blue, green, yellow, orange and red? Water molecules refract the light from the sun. Because white light is made up of many different wavelengths, and each is reflected at a different angle as it passes through the water molecules, the light is divided into its primary components. Sorry, I know. We got all technical again.

An expensive-for-its-size electronic device called a spectral illuminance analyzer or a spectrometer can analyze the frequency content of a light source. The spectrometer works precisely the same way that a real-time audio analyzer (RTA) looks at the amplitude of the different sound frequencies produced by an audio source. As you may have guessed, we’ve added one to the BestCarAudio.com lab.

If you compare the two spectrographic measurements, you can see that the water vapor in the clouds is blocking increasing amounts of green, yellow, orange and red light. Unsurprisingly, we are left with a light source that makes everything look dull. This is because the water vapor in the air has quite literally filtered out the light energy that makes colors pop.

The software scales the measurement window to make it easy to see energy levels at different wavelengths. This is similar to the way our eyes or the iris and shutter on a camera work together to deliver a similar level of perceived brightness for a given lighting condition. The chart below shows both measurements overlaid, one on top of the other. You can see that the overall brightness level on a cloudy day is significantly lower.

The measured light level was 106,252 lux on a sunny day, whereas the cloudy day was only 9,069 lux. Converted to candlepower, the numbers are 9,874 and 843.

Headlight Bulb Color

When it comes to the headlights on your car or truck, bulbs come in various colors for a variety of reasons. At the incandescent end of the spectrum, most have a yellowish look. With that said, halogen bulbs (which use iodine and bromine gas) have less yellow and produce more light output than old bulbs that use argon. Here’s the spectrographic analysis of a relatively simple halogen light bulb.

As you can see, there is a lot of energy in the red portion of the light spectrum produced by this bulb. To be clear, it’s not an amber bulb, though; we should find one of those and test it as well.

OK, we’re back from the hardware store with a pair of Sylvania 3057AK amber turn signal bulbs. The graph below shows their spectral energy.

How we perceive the color of a light source is dependent on the frequency content of the energy coming from the bulb. Warm light will have more red energy, where a cool bulb will be bluer.

Color Temperature and Color Space

If you’ve ever shopped for HID headlight bulbs, you know their color is often described by a specific Kelvin value. For example, a yellow fog light bulb might be rated at 3,000 K, where a factory-installed HID or LED bulb might be a very pure white rated at 6,000 K. Those bulbs with a very blue tint are often up in the 8,000-10,000 K range.

Most people think these values are somewhat arbitrary, but the reality is, the light color can be measured with impressive accuracy using the right equipment. Our spectrometer can do this quickly and easily. The software will also plot the measurement on what’s called a color space chart. The chart outlines the level of red, green and blue in the light source and uses X and Y coordinates to describe the location on a chart. For our testing, we’ll use the CIE 1931 color space chart. The image below shows us where our measurement of the Wagner bulb falls.

The software tells us the Wagner light source has a correlated color temperature of 3,174 kelvins. As mentioned, that’s considered a warm yellowish light. The amber Sylvania bulb has a color temperature of 1,857 and falls into the orange and red portion of the light spectrum.

White Light Isn’t Always Made Up Of All Frequencies

The last item we’ll touch on in this article is a bit of a tease toward some future content we are working on. If you’re reading this, then you’re likely looking at a computer or smartphone screen. The light created by that screen is made up of tiny red, green and blue pixels. The colors you see depend on the intensity of each of those pixels. If the screen is to be blue, then only the blue pixels will be illuminated. For violet, the red and blue will be turned on. Yellow is produced by red and green. You can easily see this pattern by looking at the CIE 1931 color space images above.

What might be surprising to some is that the perception of white can be made up of specific amounts of red, green and blue light. The chart below shows a measurement of the light produced by the laptop screen on which this article was created.

Behold! Our Dell XPS 13 laptop screen is perceived as white, yet it’s primarily red, very light green and mostly blue light. Here’s how the white light it produces measures on the CIE 1931 chart.

Our screen has a correlated color temperature of 6,662 K. If we were scoring it on even whiteness, that’d be an excellent result. But does this score mean it’s a perfect source of white light? Absolutely not! We’ll leave you to ponder that thought as we prepare the next few articles.

Lead-in Image: Thanks to Josh Matthews for sharing this photo of an Acura RSX equipped with decidedly blue headlights.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

As fall approaches, we find the sun setting hours earlier than it did in the summer. With this increase in darkness, we need to rely on the forward lighting systems in our cars and trucks to keep us safe. In this article, we are going to look at the importance of making sure your headlights are aimed properly. Proper horizontal and vertical adjustments will ensure that you can see far enough down the road to react to obstacles or avoid animals. Of equal importance, aiming your lights so that they aren’t blinding oncoming drivers is crucial to those drivers staying in their lane and not colliding with your vehicle. The science and process are simple, but they’re often overlooked.

Headlights Are an Important Safety System

In addition to your vehicle’s tires and braking system, your headlights are one of the most critical safety systems on your vehicle. If you can’t see far enough down the road when it’s dark, you won’t have time to react to objects in your path. At 60 miles per hour, you and your vehicle are covering 88 feet per second. Given than most humans have a reaction time of about one half of a second, and it takes another half of a second to move your right foot from the gas pedal to the brake, you’ve already traveled 80 feet. Now, consider that the average vehicle requires between 120 and 145 feet to stop from 60 mph, and you’ve likely traveled at least 200 feet.

Most low-beam lighting systems provide useful output to a range of 100 feet. Some of the better HID and LED systems are bright enough to illuminate 150 feet in low-beam mode. Driving at a speed where you don’t have enough time to stop because of your lighting system’s limits is called overdriving your headlights.

How Can You Upgrade Your Lighting System?

Upgrading the lighting on your vehicle involves two factors. First, you need a light source that is bright enough to illuminate the road at a distance that gives you enough time to react safely. Next, your lights need to be aimed perfectly to make use of their output capabilities. If your lights are aimed down at an angle of five degrees, then the area in front of your vehicle might be bright, but you’ll never see more than 100 feet down the road. Conversely, having your lights aimed horizontally might provide good long-distance vision, but this can lead to your lights blinding oncoming drivers. A driver approaching you who cannot see the edges of the road or your vehicle is as dangerous as you not seeing where you are going. Proper headlight aiming is paramount!

When Should I Have My Headlight Aim Checked?

The first sign that your lighting system needs adjustment would be that oncoming drivers are flashing their high beams at you as they approach. Blinding an oncoming driver is extremely dangerous. Likewise, if your lights don’t light up the rear bumper of a vehicle a car’s length in front of you, they need adjustment.

If you have made any modifications to your vehicle, you should have your technician check the headlight alignment. Changes to tire diameter or suspension height, especially if you have installed a leveling kit or lowering springs, require that the lights be adjusted. If you have added weight to your vehicle in the form of a stereo upgrade with a subwoofer system, the additional mass in the rear of the vehicle may also necessitate a change in light aiming.

Let’s Talk About Headlight Aiming Angle

The farther your lights are above the road, the steeper they can be angled downwards while still allowing you to see approximately 150 feet in front of the vehicle. Many websites cite a specific angle that is deemed to be suitable for all applications. The reality is, the specific downward angle of the beam depends on their distance above the ground. If someone says two degrees is the right angle, but your lights are 18 inches off the ground, you’ll only have light for 43 feet in front of your car. If you have a truck with the lights 36 inches above the ground and set the lights to the same angle, you’ll have light for 86 feet. Likewise, the suggestion that a fixed amount of drop is suitable also fails to compensate for differences in bulb height off the ground.

Have Your Headlights Adjusted for Maximum Safety

When it’s time to have your headlights adjusted, we’ve developed a simple process that makes the adjustment reliable and efficient. Before the technician begins any work, your vehicle must be on level ground with the tires inflated properly. Ideally, whatever combination of driver and passenger(s) is most common to the vehicle’s operation should be inside. Likewise, the fuel tank should be half full. If you have a truck or SUV and carry tools or supplies, have them in the vehicle. You’ll want the ride height to be typical before the measurements begin.

Step 1 – Measure the Cut-off Height

The first step is to establish the level at which the light is produced at the bulb or lens. With the vehicle appropriately loaded (as outlined above), measure from the ground to the top of the light cut-off pattern as close as possible to the headlight lens. Note this measurement for each side of the vehicle, as it may not sit perfectly parallel to the ground.

This process requires that the lights are already aimed relatively accurately. If you’ve had new projectors or bulbs installed, your tech will need to make sure the light pattern is relatively close to accurate. If a light is pointing at the sky, the remainder of the measurements will be inaccurate. They should be within a few degrees of horizontal.

Step 2 – Measure the Cut-off at 25 feet

The next step is to measure the height of that headlight cut-off at a distance of 25 feet in front of the lights. Use the same reference point used for the first measurement to set this distance. For example, if the tech measured the at-vehicle height 4 inches in front of the headlight lens, he or she should measure out 24 feet and 4 inches for this second measurement.

Step 3 – Use the Chart

Using the chart below, your technician can determine how high the cut-off should be above the ground for the distance you want to illuminate. If you drive exclusively in the city, then the 125-foot distance will work well. If you drive in the country, the extra distance afforded by using the 175-foot measurement is a better choice.

Step 4 – Adjust the Lights

Most modern vehicles have simple adjustments for vertical and horizontal alignment built into the light assembly. In most cases, a long screwdriver is all that’s required to raise or lower the light aiming to achieve the correct cut-off height.

The next step is for the technician to adjust the lights so that the drop at the 25-foot mark matches the chart. As long as both lights are close to each other in height, your technician can fine-tune the adjustment by lowering whichever light is higher so that the top of the cut-off is in line with the output pattern of the other light.

Horizontal Headlight Adjustment

If work has been done to the vehicle or the light assemblies, then your tech may need to adjust the horizontal adjustment to make sure both lights are aimed forward and that the hot spots from each light are spaced apart by the same distance as the bulbs in the vehicle. It’s crucial to make sure the lights are pointed straight ahead and not off to the left or right.

Drive Safely with Proper Lighting

There are a multitude of options to upgrade the lights in your car or truck. High-performance halogen, LED and HID bulbs can improve the capabilities of mediocre factory lighting systems. Once you’ve had these light upgrades aimed properly, you’ll be able to see farther and drive more safely. Your local specialty mobile enhancement retailer can likely help you with a complete lighting solution that includes proper pattern alignment.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.