Flying FPV by night completely differs from flying during daylight.
The main factor that limits the night flying FPV is the sensitivity of the image processing devices to light, of course. Spotting various objects or entities in time by night can be hard during the flight, and even dangerous.
From natural side, absence of moonlight and existence of clouds affect the view the most. As we are not able to obey these, we can arrange the times of flights accordingly, so the light conditions are the best possible.
From technical side, there are some possibilities how to increase the light sensitivity, to be able to see at night.
- FPV camera
We can use a more sensitive FPV camera, suitable for night flights. The major value we are after is the LUX number. The lower it is, the better the camera sees in the dark. Generally speaking, any camera with lower LUX value than 0.001 can do fine job in this area.
In cameras with inbuilt or attachable OSD there are some settings that affect the camera picture positively. The major settings are the AGC (automatic gain control – higher the better), DNR (digital noise reduction – disable best), gamma correction (lower the better), contrast (higher the better). Other setting like WDR/DWDR (wide dynamic range – enable best) can be either useful in some cases, but usually it does not help so much by pitch black. If there is an option for day/night (color/BW) setting, it is worth to set it from automatic to night only (BW). From my own experience, by setting only the AGC and DNR to the needed levels gave me a satisfactory picture, upon which I was able to fly the bird.
When choosing an FPV camera for night flying, choose the one with the biggest sensor (so more light can reach it), some of the todays cameras are already delivered with 1/2 inch CCD sensors.
A certain option is to use a camera without an IR (infrared) filter. Most of the FPV cameras are used during daylight and they come eqiupped with IR cut filters, that filter out the IR components of the light, giving more colorful and vivid picture. However, when using a camera for night flying, we need to gather all the possible light, including IR. As all CCD/CMOS cameras are sensitive to IR light, by removing the filter they will see better in the dark.
Todays best well known camera that is suitable for night flying is the one equipped with the 1/3” Sony SUPER HAD II CCD sensor, with 650TVL resolution and 0.01LUX rating. It is known for example as HS1177, PZ0420, CC1333. This camera is good for some night flying in parking lots or illuminated park spots, but still not good enough for pitch black flight.
For extreme night flying (pitch black), a camera which has much lower LUX rating is a must. There are a few technologies that can achieved that. One is the so-called “starlight” technology where the sensitivity is achieved by a special High Performance Image Signal Processor. The cameras using it usually also acquire bigger, 1/2 inch sensor and low light (F1.2) lens. The second well known technology is the so-called “sense-up”, when a camera function allows the user to select a slower shutter speed in order to let extra light into a camera. There are cameras using even sense-up 256x, however, the more sensitive the camera, the bigger the lag between the picture scanning and the output. These can be used for fpv purposes only in 2-4x ranges, to avoid blurring.
- Extra lighting (additional illumination)
Another option for getting a lighter picture by night is to use so-called illuminator devices. These are mostly PCB boards, containing a matrix of LEDs.
Note that this method can be used only in close distances, because there is no possibility to extend the visible range too far with small and light devices, onboard the multicopters. Well, there are several exceptions, for example kind of laser based illuminators, but these are not commonly used yet on copters, rather hunters use them for hunting animals by night.
If we go for an additional illumination, we have two choices, either to use a device which emits in the visible range, and a different one, emitting in the invisible (human eye, animals) range. The latter we called IR (infrared) illuminators.
For illumination by visible light, many use the already well known 3W,5W,10W LED matrix solutions or single LED chips, widely available. These are cheap, light and give out enough power for wide are illumination, even for proximity flying. The only downside (if) is that the copter is highly visible for anybody, so this solution can not be used for surveillance purposes at all.
For illumination by NIR (near infrared) light we have two choices, either to use IR LEDs or IR laser diodes. The laser diodes can emit much stronger light but because of the light pattern, they are not able to cover large degrees. They are good for large distances, where only a small spot should be illuminated. IR LEDs are, however better for short distances, when we need to cover bigger field of view.
The CCD cameras seem to be similarly sensitive to the IR light and the visible spectrum, but note that when using an IR illuminator, we need to use a camera without an IR cut filter. By using an IR emitter, we can avoid detection of the copter at bigger distances, when the sound of the motors and propellers can not be heard. The widely available emitters in the NIR range emit in range of 780nm-850nm, and the CCD cameras are the most sensitive to the 780nm. That is why it is used as an industrial standard in surveillance cameras. Some special emitting devices can even emit in higher wavelengths, such as 900nm, 940nm, 950nm, 1020nm. There is a well known issue with the IR LEDs, the so-called “glowing”. Although the radiated light is not visible for the human eye, the LEDs can be seen in the dark, as they are glowing purple. This issue is gone only when using higher wavelength LEDs, above 900nm.
Apart from the cameras and extra illumination, there are some more aspects we need to consider when performing night flying FPV. These can be:
- takeoff/landing zone illumination – can be neccessary to find back home by the end of the flight
- picking areas when there is really nobody crossing our path – it can be hard to avoid a collision with a moving object/entity
- equip the copter with all the devices possible, delegated for finding it in case of a crash – it is much harder to find it during the night
- having a “spotter”, a mate who can follow the flight – he can warn us in cases of possible collisions or other sudden events
- having a switch controllable emergency light/strobe on the copter – can warn anybody in the proximity of the copter in a dangerous situation, especially in a case that we have a stealth solution, with no visible light at all
- well-lit takeoff zone when we can see well if any repair or just battery replacement is needed
- weather conditions awareness – it is always good to know how the weather is going to be, so we can prepare for rain, fog, …