NVG Operations Trivia #1-20

The following 60+ questions, posted in 20 question sets, focus on NVG operations.  

1.  Q: NVG challenges?  
   A: Reduced field of view, limited depth perception, monochromatic (green or white only), limited range in the visible spectrum, distractions from improper adjustments, complete loss of view (due to a malfunction, obscurants, or incompatible lighting), illusions and spatial disorientation.   

2.  Q: Normal field of view versus NVG field of view?  
   A: 120° vertically and 200° laterally vice 40° vertically and laterally using NVGs.

3.  Q: Cones? 
   A: Provide color vision and high acuity used during times of high illumination.  The    highest concentration of cones is in the fovea (center of the eye). The cones are less effective in low light, resulting in low visual acuity and color perception. 

4. Q: Rods? 
   A: Rods only see in black and white and have significantly less acuity, but they are  10,000 times more sensitive to light than cones. Rods extend outward around the fovea (outside). 

5. Q: Physiological blind spot?  
   A: Present in both high and low light, the optic nerve has no rods or cones and creates a “blind spot,” which is overcome by binocular vision (overlapping of the two eyes field of vision).  

6. Q: Night blind spot?  
   A: Created by the cones’ (center of the eye/fovea) inability to see at low illumination   levels. Makes seeing distant objects directly ahead difficult. The night blind spot is   not a factor on NVGs due to high illumination levels.   

7.  Q: Night adaptation? 
   A:  Takes 30-45 mins. Takes 5-10 mins aided to unaided (after taking NVGs off).  

8. Q: What is “minus blue”?  
   A: The NVGs cannot see light below a certain spectrum. This is to allow cockpit compatible lighting to not wash out the NVGs, but it also limits the NVGs’ ability to see things like airport beacons, blue/green chem lights, green nav lights, some LEDs, etc. The unaided eye sees .4-.7 microns. Aided you see .6-.9.  

9. Q: NVG operation common misconception among the uninitiated?  
   A: You aren’t looking through the tubes you are looking at a projected image (e.g. TV screen).  

10. Q: What is gain?  
    A: The NVG’s ability to maintain a constant brightness on the output image (e.g. gain down for bright light situations and up for low light situations).   

11. Q: What is sky glow? 
    A: 1.5 hrs. after sunset and 1 hr. before sunrise the sky will be bright, making the gain decrease and detail below the horizon will be lost.   

12. Q: Effects of low moon angle  
    A: Similar to sky glow, worst when looking into the moon.   

13. Q: What is the negative effect of incompatible lighting? 
    A: In or out of the aircraft the presence of incompatible lights gains down the NVGs, decreasing acuity.   

14. Q: What is scintilation?  
    A: Caused in low light conditions, in which the gain continues to be driven up resulting in a “sparkling” effect. This is the point where the detail will become decreased as the illumination decreases.   

15.  Q: What is ideal illumination and albedo?   
    A: A quarter moon (50% illumination) is considered best because it creates varying contrasts (albedos), which aid in motion and depth perception, scene detail and spatial orientation.   

16.  Q: Moon angle considerations? 
    A: When the moon is high, you have good illumes but less shadows ,which decreases detail/contrast. At medium moon angles you have satisfactory illumes and good detail due to shadows. Low moon angles increase shadows but can “bloom” out goggles if looking into/toward the moon.

17.  Q: Orientation of low moon angle – considerations?  
    A: Low moon angles may provide excellent NVG detail one way (e.g., moon at  your back) and awful detail in the opposite direction (moon off the nose).  

18. Q: Which is the objective lens? 
    A: Outer lens. 

19. Q: Which is the diopter? 
    A: Inner lens.  

20. Q: How should you adjustment vertical and tilt settings? 
    A: Vertical and tilt should be set to allow for optical axis alignment. The diopter lens should be about 1 inch from your eye, allowing you to comfortably see below the goggles to your instruments. Because you are looking at “TV screens”, bringing the diopter lens closer will not increase your field of view.