Key takeaways
- Know your numbers: Lumens measure brightness; candela measures beam intensity — both affect performance in different ways
- Ratio matters: Use the candela-to-lumen ratio to evaluate whether a light offers broad coverage or focused throw
- Test your gear: Don’t rely on specs alone — function-check and test lights in real-world conditions
- Train for conditions: Understand how light behaves in different environments to avoid backlighting and maximize threat visibility
By Tom Stilson
Whether fresh out of the academy or decades into a career, every law enforcement officer seems to have an abundance of flashlights on hand. Over the past 10 years, handheld and weapon-mounted lights have improved more dramatically than over the previous 30 years. While owning the latest and greatest light isn’t bad, what practice or testing was done before using it? Ultimately, by knowing a flashlight’s capabilities and performance, we learn how to effectively use one of the most critical tools on our duty belt. But where does the learning start, and how do we apply this knowledge to our profession? For today, let’s start with candela and lumens.
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Understanding candela and lumens
In scientific terms, a lumen (lm) measures the flow of light from the source. Candela (cd) measures the light’s intensity at its brightest point. Since not everyone is scientifically inclined, let’s replace the light with a fire hose. The hose’s flow rate is analogous to lumens, while the nozzle’s highest point of flow is candela. For example, a jet spray has higher candela, while a wide spray has lower candela despite having the same flow rate (lumens).
Two lights with the same lumens can produce very different illumination patterns depending on their candela. As an unsolicited piece of advice, don’t rely solely on lumens for flashlight purchases. While I’ve rarely heard a night shifter — myself included — complain about “too much” light, more lumens doesn’t guarantee that light will perform to your needs. Ultimately, lights are strikingly similar to duty ammunition. They must be function-checked, grouped and sighted in for your applications.
While testing various lights for this article, I found the best means of communicating light performance was through a candela-to-lumen ratio (cd:lm). The candela-to-lumen ratio acts as a reference for comparing flashlights of varying luminosity and candela. For example, the Surefire X300 Ultra, with 1,000 lumens at 11,300 candela, has a ratio of 11.3. Meanwhile, the Surefire X300 Turbo, with 650 lumens and 66,000 candela, has a ratio of 101.5. While a visual side-by-side comparison of the Turbo and Ultra shows obvious differences in their respective light beams, the candela-to-lumen ratio confirms this with nearly an order of magnitude difference between the lights. Thus, the candela-to-lumen ratio is a numerical representation of where a light’s beam lands on the spectrum from flood to spotlight.
By comparing the candela-to-lumen ratio between lights, a picture develops of the performance characteristics across different brands and models. In another example, the Streamlight TLR-1 HL-X, with 1,500 lumens and 20,000 candela, has a ratio of 13.3 cd:lm. When compared to the X300 Ultra with 11.3 cd:lm, both lights have similarly wide beam patterns.
Illumination and distance
Whether searching between dense houses and industrial buildings or fields and overgrown woods, duty lights should produce enough illumination to positively identify threats at reasonable distances. This begs the question — what is reasonable? While many light manufacturers list beam distances of 200 meters or more, rarely can the human eye identify a threat at that distance without magnification — especially at night. This consideration is why I ultimately chose to evaluate lights of varying candela and lumens at approximately 50 meters.
While the higher candela-to-lumen spotlight beam easily points others to where your attention is directed (and at greater distances), they cover a relatively narrow search area. The Surefire X300 Ultra 1,000-lumen (11.3 cd:lm) easily illuminates a width over 15 meters at objects 50 meters away. Even with lower lumen output on the X300 500-lumen version (13,000 cd and 26 cd:lm), the illumination width is similar — just not as bright. However, the Surefire X300 Turbo (101.5 cd:lm) illuminates a width less than 10 meters at objects 50 meters away. This disparity in illumination coverage is worth consideration.
When searching large areas, lower candela-to-lumen lights provide great coverage if equipped with enough lumens. Otherwise, the light won’t have the intensity to positively identify potential threats. High candela-to-lumen lights maximize a lower amount of lumens by focusing the beam into a spotlight and perform well at greater distances. Higher ratio lights also reduce spill, which minimizes the likelihood of backlighting another officer.
Switching perspectives
Lights are more than an aid for navigation, searches and threat identification. With the overwhelming brightness of many lights today, handheld and weapon-mounted lights also suppress the suspect’s ability to see you. In addition, they can momentarily disorient a suspect and buy us precious time in the action-reaction gap. Ultimately, duty lights should be approached from the suspect’s perspective as well.
Tactical quick hits
- 🏭 Clearing a warehouse? You’ll want a high-candela beam to cut through long distances.
- 🚪 Searching a small room with reflective surfaces? Avoid overpowered lights that cause backscatter.
The Surefire X300 Ultra and Turbo were used in the following example as the extremes of low and high candela-to-lumen ratio lights. With a “suspect” positioned 25 meters in front of an “officer,” the Turbo and Ultra impaired the suspect’s vision with no apparent difference. However, if the suspect moved laterally by a few feet, the effect on the suspect’s vision changed between the two lights.
With the Turbo’s high candela-to-lumen ratio, the suspect’s vision was not significantly impaired like it was before. In the case of the Ultra’s lower candela-to-lumen ratio, the suspect’s vision remained impaired. This reiterates the earlier point: while a high candela-to-lumen beam is useful for minimizing unintended illumination and seeing over longer distances, the tight beam is less effective at suppressing unknown threats over large search areas. In no way is this a condemnation of high candela-to-lumen light setups — rather, these are tactical considerations for utilizing such lights.
Broader considerations
For those who’ve taken a crime scene photography class or two, you’re probably familiar with diffuse lighting, shadows and hot spots — and how they affect the quality, clarity and presentation of photographs. Artificial lights have similar considerations with backlighting, front lighting, reflections and casting. A little work with you and a partner role-playing between good guy and bad guy can go a long way in understanding and seeing these issues in practice.
Training tips for flashlight use
- 🧤 Practice light activation under stress with gloves on
- 🌆🌲 Train in urban, wooded and interior environments to observe beam performance
- 👀 Partner up to test lights from a suspect’s perspective
Hundreds — if not thousands — of scenarios are possible, but there are a few worth highlighting. First, I already touched on backlighting as an example of improper light use. In those instances, the user inadvertently projects light onto another officer’s back, silhouetting them. Conversely, a light’s spill can cause issues with front lighting. Front lighting occurs when the wider beam of a lower candela-to-lumen light reflects off surrounding objects and back onto the officer. This potential drawback is an important consideration when working with such lights.
I’ve encountered the occasional officer who argues against a light that’s “too bright.” Unfortunately, “too bright” is an arbitrary and unrealistic unit of measurement. In my experience, lights are “too bright” when the user activates the light in close proximity to — and perpendicular to — a reflective surface, such as a window, mirror, or lightly colored surface. Those situations are largely unavoidable with any kind of modern handheld or weapon-mounted flashlight exceeding the 500-lumen range. However, proper practice and tactics tend to minimize or eliminate such problems. In short, candela and lumens aren’t the problem — it’s most likely the operator.
Final thoughts
Law enforcement is governed by many hard rules such as constitutional law, case law and statutory mandates. Luckily, the handheld or weapon-mounted light you choose has far greater discretion and forgiveness. Regardless of the lumens, candela, or ratio thereof, there is no free lunch — and familiarization with your light is critical for maximizing effectiveness. After all, no amount of lumens or candela can overcome a complete lack of knowledge and practice. While the knowledge may have started here, successful application depends upon the user. No matter the setup, don’t shy away from practicing with your lights so you can keep yourself — and your brothers and sisters in blue — safe.
Pre-shift light check
- ✅ Have I tested my light at 50 meters?
- ✅ Do I know its candela-to-lumen ratio?
- ✅ Can I identify threats without backlighting my partner?
- ✅ Do I carry a backup light with different beam characteristics?
About the author
Tom Stilson has been a law enforcement officer since 2015, serving in numerous roles including patrol, SWAT, and criminal investigations. He holds a B.S. from Stanford University in Geological and Environmental Sciences and uses that background to take a science-oriented approach toward training, tactics and law enforcement. Tom holds certifications as a Field Training Officer, POST Firearms Instructor, POST Generalist Instructor, Major Crimes Investigator and SWAT.
