Description
Object description
A training film for all personnel who work at night, with a particular emphasis for pilots and aircrew who fly at night. The structure of the eye is examined, followed by a series of preventive measures to minimise the loss of night vision. The critical concept of light adaptation is emphasised.
Content description
Reel one:
Film opens with an owl at night whose vision has evolved over many years to cope with the dark environment in which it prefers to live. Such eyes may be compared to an expensive camera (Leica) producing images in almost total darkness. In an animated diagram, the human eye (the retina) is compared with camera images; they are equivalent in performance. The retina is explained.
"Rods": Rods and visual purple; explained. The owl's night vision is largely due to the type of cell known as rods.
"The human eye": Several animated diagrams are presented to help the narrator explain the human eye: other cells known as cones are found around the central axis of the human eye, this area, the fovea, is used for seeing detail in daytime vision. The effect of incident light falling on the retina; how to search an area at night: by looking off centre (of the eye's central axis) vision using the rods, then use the cones to add detail to the images revealed by the rods. A clear narrative explains in detail.
"Scanning": Systematic scanning is a technique to ration the energy used by the eyes; diagram with explanation.
"Night-time visibility": Two factors determine night-time visibility; contrast and object size; contrast is the change in tone between an object and its background. Cut to night view of tree obscured intermittently by bubbles of clouds passing by.
"Adaptation": Sensation: a sudden beam of bright light leads to temporary glare. The eye adjusts itself involuntarily to give normal vision in the brighter light, known as light adaptation. Within the eye, the iris protects the retina in bright daylight conditions. Analogy with the variable diaphragm of a camera lens.
"Strong light / weak light": Diagram shows the effect of the iris; rods depend upon their stock of visual purple which is bleached by the effect of light; another animated diagram shows the difference between sensitive and bleached states of the eye: full sensitivity in night conditions is reached after 35 minutes (starting at zero and no flashes of light): a sudden flash will bleach the eye, to the level at the zero point again, almost instantaneously. The night vision is lost for 35 minutes.
Example shown of a dispatch rider, static and reading map by torch- light, extinguishes torch, and drives straight into a ditch.
Content description
Reel two:
"Pre-adaptation goggles": The effect of red light upon the eye – explained – has very little effect on the cells of the eye. Cut to airman wearing dark lenses pre-adaptation goggles, reading a paper in the rest room prior to his night flight to Germany; once obtained, he is preserving his night vision, taking care not to expose his eyes to any white light.
"Instrument lighting": Film cuts to the illuminated dials (the basic six grouped together) in an aircraft; care must be taken by the pilot not to stare too long thus preserving his night vision. The illumination of the basic six can be dimmed by the pilot to suit his vision.
"Notes for navigators": In the aircraft work with the minimum of light, cover one eye with the hand to maintain sensitivity. The narrator notes that fatigue and smoking can reduce night vision.
"Vitamins": A lack of vitamins can reduce night time vision. Cut to a pile of carrots – eating these cannot help your vision!
"Oxygen": Flying at heights above 15,000 feet, the lack of sufficient oxygen is the most important factor that leads to a loss of sensitivity; oxygen will help restore night vision, but can take up to 15 minutes. Explained with the animated graph seen in reel 1. The study of vision and the human eye supplies material for a lifetimes study. Cut to a row of medical books in the Ophthalmic Consultants room; he takes down a book, referring to a series of diagrams illustrating the elements of the eye as the narrator summarises the information presented in this film.
Film closes with a pilot in the rest room, not wearing his pre-adaptation goggles, who is summoned to his aircraft, taxis to the runway and into a tree.