The impact of alignment on illumination is significant. Just 24 inches off centerline substantially reduces the light.
Utilizing the Wall of Light you established as you initiated the stop, approach the vehicle from the rear of your car. Do not cross between the vehicles. As you approach the vehicle have your handheld light ready to switch on but wait until you are positioned for the best tactical advantage before you light up the occupants of the vehicle.
Now let's discuss the driver's side approach. This is by far the most common method used today. For some officers it is the only way they ever approach, although I would encourage everyone to have more than one technique in their arsenals for any law enforcement-related task, including vehicle approaches.
On a driver's side approach, the driver's side mirror is often an aiming point for my handheld light, especially when the patrol spot is aimed at the interior rearview mirror. The majority of the time this technique will result in complaints from the vehicle's occupants, but it will allow you to gain a small advantage while more clearly assessing the vehicle's interior. A simple apology about not realizing you aimed the light into the vehicle will often be met with the occupant saying, "No, you didn't shine it in the car. It reflected in the mirror."
Now that we have reviewed the basics, let's try to understand why light is so critical to our overall survival and learn how to better deploy low-light techniques on future traffic stops.
There seems to be a lot of confusion as we discuss light power/brightness. Most modern flashlights are rated in lumens. A lumen is a way of measuring how much light gets to what you want to light. One lumen is equal to one foot-candle falling on one square foot of area. A foot-candle is how bright the light is one foot away from the source.
Candlepower and a foot-candle unit of measurement are not the same. Candlepower is a measure of light taken at the source of light, not at the object being illuminated. Foot-candles measure the light directed at the object being illuminated.
On a traffic stop, our headlights are our primary method of seeing at night, but the benefits of these lights can be very limited. The angle from the center of the light beam and the distance the object is from the light source are critical factors.
Look at the chart above and note the light meter readings taken at 5, 10, 20, 40, and 50 feet from the headlight surface of a 2012 Dodge Charger patrol unit. The second set of measurements from the same distances but just 24 inches off the centerline of the beam are significantly lower than the centerline results.
This is important for many reasons. The first being how it relates to the distance between the subject vehicle and your unit. Consistency on your part here will result in similar light conditions and ultimate visibility with each stop. The drastic drop in light illumination as measured off the beam's centerline is critical to the vehicle's offset when you position the unit. So is knowing this drop in illumination can be an asset on the approach and while maneuvering around the vehicles.
The Wall of Light you have established has many advantages if your vehicle is properly positioned. Proper vehicle position and your approach technique will limit your body silhouette as you approach.