Why two lamps?
Adding a second lamp does not increase the size and weight of your pack, but it doubles the amount of light available to the camera. It is like gaining an extra f-stop on a still camera. However, to realize another increase in light, you would need to double again: four IR lamps. That is getting a bit unwieldily in the field. Also be aware that newer "widescreen" aspect HD cameras are shooting such a wide 16:9 aspect ratio landscape image, you will need two IR lamps to feather across the field of view and fully fill the frame. If you are shooting standard 4:3 aspect video, one IR lamp will fill the frame. Forcing a modern camera into 4:3 aspect ratio means you will be giving up the advantage of the wide angle lens on the camera and may have to be further away from your subject, possibly making it more difficult to light.
Camera models are refreshed as quickly as every 6 months and we don't have a list of current models with the NightShot feature, so you'll have to do your own research using the recommendations below.
NIGHTSHOT FUNCTION: first and foremost this feature must be included or you simply cannot film in IR light. Check the Sony specs for NightShot mode, and even the manufacturer's photos of the camera to verify there is NightShot button on the exterior (usually under the fold out LCD display. Only the high-end consumer grade Sony cameras have this feature.
SENSOR SIZE: Bigger captures more light and therefore is better. For reference, in 2016 the Sony FDR-AX53 contained a 1 and 2/5'' sensor, the largest available at the time with the NightShot function. This camera can be bought using the Amazon link at the bottom of this page. Sensor size is always found in the tech specs of the camera.
HARD DRIVE/SD CARD: Old NightShot-capable cameras may record to DVD or Mini-DV formats, these are cumbersome to use with modern digital video workflows for archiving and editing purposes and probably should be avoided if you are editing video on a regular basis.
CAMERA SETTINGS: Generally speaking, use at least 1080 movie size, or larger. The data rate should always be set to the highest possible "recording quality". "Low Lux" feature, if available, should be on (newer cameras are so sensitive you may experiment with this off if the subject is close). Anytime a tripod is used, "Steadyshot" should be off. "Focus peaking" is a visual representation of what parts of the image are in focus, so we recommend that be on if available. Once your image is in focus, press the "manual focus" button to lock it in place and keep the camera from inadvertantly attempting to focus on passing insects, etc.
LIGHTING TIP: If you use "off camera lighting" techniques by placing lamps 3 feet or more away from the camera, the textures/shadows this generates will give your video a more 3-dimensional look rather than a flatly lit scene. This also reduces or eliminates "floating ghost orbs" caused by the light hitting out-of-focus dust particles near the lens or bright flashes of movement cause by a moth buzzing by. (Insects are not attracted to IR lamps!)