TD53 Flashcards
(10 cards)
Discuss the characteristics of photographic mesopic and scotopic vision
Photopic vision
Experienced during daylight and under high levels of artificial illumination sharp image interpretation and color vision.
Central vision
cones
Mesopic
At Dawn dusk in under full moonlight
Vision is achieved by a combination of rods and cones
Visual acuity steadily decreases with declining light
Most dangerous
Scotopic
Low light environment such as partial moonlight and starlight conditions
Cones become ineffective in these conditions causing poor resolution in detail
Visual acuity decreases to 20/2 or less and color perception is lost
A central or night blinds might occurs when cone sell sensitivity is lost
Scotopic vision degrades primary color perception, two shades of black, gray and white and less. The light source is of adequate intensity to stimulate the peripheral vision is used primarily while viewing with scotopic vision
Define and describe the process of dark adaptation
The process by which the eyes become more sensitive to low levels of illumination
Rhodopsin (visual purple) is the substance in the rods responsible for light sensitivity. The degree of dark adaptation increases as the amount of visual purple in the rods increases through biochemical reaction
Lower starting light level faster adaptation
How long does it take to fully dark adapt when exposed to Bright light? How long does it take to recover to complete dark adaptation
Dark adaptation for optimal night vision acuity approaches its maximum level in about 30 to 45 minutes under minimal lighting conditions
Depending on brightness (intensity) and exposure duration or after repeated exposures, complete dark adaptation recovery time can range from several minutes to 45 minutes or longer
What are the differences between rod and cone cells?
Cone sales are primarily for day or high intensity light vision( viewing periods or conditions)
The rods are used for night or low intensity light vision
Some characteristics of day and night vision are due to the distribution patterns of rods and cones on the retina
The center of the retina, the fovea, contains a very high concentration of cone cells but no rod cells. The concentration of rod cells begins to increase toward the retina’s periphery
Describe how exposure to Bright sunlight can have a cumulative and adverse effect on dark adaptation
Exposure to intense sunlight for 2 to 5 hours decreases visual sensitivity for up to 5 hours and also decreases the rate of dark adaptation and degree of night visual acuity. These cumulative effects can persist for several days
What is dark focus
When light levels decrease the eyes, focusing mechanism might move toward a resting position, making the eye more myopic. These factors become important when crew members rely on terrain features during unaided night flights. Special corrective lenses can be prescribed correct night myopia.
During tactical operations at night, how should the cockpit lighting be adjusted?
Instrument cockpit and rear cargo area Overhead lights should be adjusted to the lowest readable level that allows instruments, charts and maps to be interpreted without prolonged, staring or exposure
For airports with three-step pilot controlled lighting systems, how do you turn the lights to low medium or high intensity levels? How long will the light stay on?
Seven times within 5 seconds for high intensity
Five times medium intensity
Three times low intensity
All lighting is illuminated for a period of 15 minutes from the most recent time of activation and may not be extinguished prior to the end of the 15 minute.
If illumination is insufficient, how should an aviator perform a takeoff to ensure obstacle clearance
Altitude over airspeed takeoff until the aircraft reaches in altitude that clears obstacles
Night or nvg considerations to task 1058 perform vmc approach
- Altitude apparent ground speed and rate of closure are difficult to estimate at night. The rate of descent during the final 100 ft should be slightly less than during the day to avoid abrupt attitude changes at low altitudes. After establishing The descent during unaided flights, AirSpeed may be reduced to approximately 50 knots until apparent. Ground speed and rate of closure appear to be increasing. Progressively decreased the rate of descent and forward speed until termination of maneuver.
- Surrounding terrain or vegetation may decrease contrast and cause degraded depth perception during the approach. Before descending below obstacles determine the need for artificial lighting.
Use proper scanning techniques to avoid spatial disorientation
When performing operations during unaided night Flight, ensure that the searchlight or landing light is in the desired position. Using the light will impair night vision for several minutes. Exercise added caution or in resuming flight before reaching full dark adaptation.
