Red Light Blindness
Red light blindness - the visual handicap that develops gradually affects most pilots including many that seem to have "perfect vision" under daylight flying conditions.
A good idea, if you are a pilot over the age of 40 years young, is to try and read fine print by red light before your next night flight.
What is red light blindness? Heres an example: You plan on taking your wife out to dinner at a local "feeding hole" located at a convenient airport about an hours flight away from where you hanger your plane.
You leave just a little after sunset in perfect weather. You need to cross-check your position and make sure the frequency of the next VOR is correct. Its dark in the cockpit so you turn on the red map light and spread a chart on your knees. You can't read it there so you pick it up for a closer look..yikes, it is still blurred. You move the chart right up under the red map light, you sense your eyes are widening and your forehead strains as you try to focus the fuzzy figures of the VOR frequency. Thats red light blindness.
How does red light blur vision?
At the age of forty your eyes ability to focus close up declines due to changes in the ability of your lens to alter its shape to clearly focus an image on the back of your eyeball. (the retina) This condition is called presbyopia.
In good illumination it is hard to read a newspaper held at arms length. I remember going through this and I will bet you have too. Red light has a rather long wave-length. It takes even more effort, on your eyes part, to focus on print in red light than in normal white light illumination.
The pupil of the eye dilates to its maximum under dim red light, attempting to admit more light to the retina. The net result from the lens thickening and increasing its curvature and the dimness of the red light causes the image to fall slightly behind the retina.
I will high-light several sources that will include diagrams to ease your understanding of eye physiology which is beyond the scope of a short blog.
If you have an interest in photography the human eye is similar in operation. If you are near-sighted or far-sighted click on the links in this sentence.
A good idea, if you are a pilot over the age of 40 years young, is to try and read fine print by red light before your next night flight.
What is red light blindness? Heres an example: You plan on taking your wife out to dinner at a local "feeding hole" located at a convenient airport about an hours flight away from where you hanger your plane.
You leave just a little after sunset in perfect weather. You need to cross-check your position and make sure the frequency of the next VOR is correct. Its dark in the cockpit so you turn on the red map light and spread a chart on your knees. You can't read it there so you pick it up for a closer look..yikes, it is still blurred. You move the chart right up under the red map light, you sense your eyes are widening and your forehead strains as you try to focus the fuzzy figures of the VOR frequency. Thats red light blindness.
How does red light blur vision?
At the age of forty your eyes ability to focus close up declines due to changes in the ability of your lens to alter its shape to clearly focus an image on the back of your eyeball. (the retina) This condition is called presbyopia.
In good illumination it is hard to read a newspaper held at arms length. I remember going through this and I will bet you have too. Red light has a rather long wave-length. It takes even more effort, on your eyes part, to focus on print in red light than in normal white light illumination.
The pupil of the eye dilates to its maximum under dim red light, attempting to admit more light to the retina. The net result from the lens thickening and increasing its curvature and the dimness of the red light causes the image to fall slightly behind the retina.
I will high-light several sources that will include diagrams to ease your understanding of eye physiology which is beyond the scope of a short blog.
If you have an interest in photography the human eye is similar in operation. If you are near-sighted or far-sighted click on the links in this sentence.
