Bad guys avoid sunlight. Darkness is nearly always an advantage for doing things one isn't supposed to be doing. Most cops still rely on a flashlight as their primary aid against darkness, but there are other and better tools available. Night vision gear is still a lot more expensive than a flashlight, even though prices are falling and the gear is more portable and better-performing than ever before.
Night vision gear falls into two major categories. Light amplification equipment, as the name suggests, boosts available light to useful levels. These devices are also called "image intensifiers." They work well under most conditions, but are dependent on there being some light to amplify. They are ineffective in pitch darkness. Infrared (IR) equipment is sensitive to differences in temperature and light outside the range of the visible spectrum. IR viewers are also called "thermal imaging" equipment.
Active and Passive Infrared
IR gear can be active or passive. Active IR emits IR light like a flashlight, but the IR rays are almost invisible without an IR-sensitive viewer. If you look directly at an IR light source with bare eyes in low visible light, you'll see a faint red glow. Passive IR picks up objects radiating heat as compared with their surroundings. It works best in cooler temperatures, when people and vehicles are much warmer than the air and stand out better.
Active IR is an increasingly common feature on surveillance cameras, especially those used at entry doors. The usual configuration is a ring of IR light-emitting diodes (LEDs) surrounding the camera lens. These do have a faint glow when active, but are usually no more noticeable than other electronic gear with a standard LED power indicator. The image viewed through the camera is as clear as one illuminated by regular visible light, although colors and shading may be distorted as compared to the way they would appear in visible light.
Officers should watch for this kind of equipment, as it is sometimes used to detect the approach of law enforcement toward meth labs, marijuana grow houses, and other locations where the occupants want to know when the cops are coming.
Some handheld night vision devices have active IR emitters, but the advantage of these is reduced as compared to a visible light flashlight. There is considerable fall off in visibility as the distance from the light source increases. Beyond 50 feet of so, most portable devices don't put out enough IR light to illuminate objects clearly. The biggest advantage of IR is in its ability to pick out relatively warm features such as people, animals, and vehicles that are or have recently been running.
FLIR H-Series Thermal Imagers
FLIR is one of the more prominent manufacturers of IR equipment. Forward-looking infrared cameras are standard equipment on public safety aircraft and give the company its name. FLIR sent me one of its new H-Series tactical thermal night vision cameras to try out and evaluate.
The H-series is about the same size and weight as a set of surveillance binoculars. The sample I used has a monocular eyepiece with a large silicone rubber gasket. The gasket has internal leaves that spread open when the eyepiece is pressed against the user's face. This keeps stray light from the display from leaking out and possibly revealing the user's location to a surveillance target.
In cold weather (about 30° F), it took the camera display about two minutes to change from a color bar pattern to a cloudy image, and another three to five minutes for that image to gain clarity. There is a setting that keeps the camera in standby mode and reduces the time required to bring it to a fully active state, but this also reduces the useful battery life. Once the device was fully warmed up, looking through it on a moonless night revealed an unseen world.
Rooftops glowed slightly as they radiated heat from inside. Cars that were running or had recently been parked stood out clearly from those that had been sitting idle. People and animals might as well have been wearing reflective clothing and standing in a spotlight.
My black dog was invisible to the naked eye, but when seen through the H-Series camera he was solid white, as was the spot on the grass where he had just relieved himself. I placed my hand on a piece of siding on the outer wall of my house for a few seconds, and could then see the outline of where it had been through the camera. I couldn't help but imagine what I could have done with one of these in my days in patrol on the graveyard shift.
The model I used had weatherproof rubberized buttons on top for zooming the image 2X and back again, reversing from black-on-white to the opposite, and for recording a still or video image to an internal SD memory card. The images are watermarked with a FLIR logo and the time and date. The camera comes with a protective case that also holds an AC and car charger and a shoe that connects the charger and/or a tripod mount. The camera lens is protected by a flip-down cover. The longest time I used the camera was about two hours, which drew the power indicator down to around 80 percent.
The H-Series pricing starts at $4,999. That's a large chunk of money, but I could see one of these cameras serving an entire shift so long as the unit that was carrying it was able to go where it was needed. Where it might take an entire squad of officers to search a field or warehouse safely, one of these cameras would reveal anyone there in short order, and take the person's picture to boot.