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What’s the Best Night Vision Lighting for the Color Blind?

We had a discussion at the last board meeting about the best type of lighting for the observatory to preserve night vision. Our librarian Scott Harlow raised a concern that colour blindness may need to be addressed in our observatory low-level lighting set up. Some board members replied that they thought colour blindness was principally a problem of distinguishing colour accurately. They thought that even if a color blind person couldn’t distinguish color, they’d still see the lighted area. Scott responded:

“I agree with the comment of colour blindness reducing to discernment of colour, particularly red and green regions of the visible electromagnetic spectrum for a small but significant percentage of the male population, but only insofar as comfortable ambient light levels are concerned. However, it’s a different kettle of chromatic fish under conditions of low ambient lighting levels. If someone has issues discerning colour under ordinary diurnal conditions then I assert that in nocturnal environs if a bandwidth is employed at low intensity, and the viewer’s sensitivity is substandard in the utilized region, then the person so afflicted will not see as ably as one not so afflicted. As such there poses an increased risk of damage to people and property from inadequate illumination… My suggestion is that we employ low-intensity LED lighting that factors in the population suffering from sensitivity dropouts, whether amber LED frequencies best serve the purpose I don’t know….”

Dr. Bruce Woodburn, MD, FRCS (C), the director in charge of our Light Abatement efforts and a local ophthalmologist, looked into this and this is what he had to say:

 

“Scott is right. Amber light would provide functional ambient light, even for the ‘color blind’, without affecting dark adaptation. To understand the issues, a few points must be kept in mind.

 

“’Color’ is a sensory phenomenon that occurs in the brain after a huge amount of information processing by the visual system. It corresponds only approximately to the frequency distribution of light wavelengths entering the eye. Your plaid lumberjack shirt has the same colors at noon and dusk, viewed under very different lighting conditions. The same color can be produced by very different spectra, and one spectra can produce very different colors.

 

“The 3 color pigments in the cone receptors are called ‘red, green and blue’ but have wide, overlapping sensitivities. The green and red sensitivity curves overlap widely. When we ‘see green’, it’s not because the green receptors are stimulated and not the red. Rather, the green receptors are stimulated 30% more than the red and the visual system interprets this as pure green.

 

“’Color Blindness’ is a large group of disorders with many different causes. People with “color blindness” are seldom blind to colors, they just perceive them differently and have difficulty differentiating similar colors. The most common color blindness’s are red/green.

 

The majority of these ‘red/green color blind’ people have a defect in their red pigment so its absorption spectra is closer to green. They have difficulty differentiating red from green. They can see red and green traffic lights, but they appear the same color.

 

“A small proportion of patients (less than 1% of the population) have no functioning red pigment. Not only are they unable to differentiate colors, but they cannot see light in a small portion of the red spectrum where their green pigment has no sensitivity. A green traffic light appears normal, but a red light appears dark. These ‘Protanopes’ would be unable to see the red light illumination from a red LED, but would be able to see amber light.

 

“This makes more sense if you can look at absorption spectra of pigments and emission spectra of LED’s:

 

human vision

 

“Note: Rods (dashed black line) do not respond to red LED emission light. Hence dark adaptation is unaffected. Rods have a small response to orange LED emission, so red is preferable for the 99% of the population with normal red cone function.

 

“If you are interested in this stuff, read up on the evolution of colour pigments. When I was a kid, the received wisdom was that humans had the best colour visions, and ‘animals’ saw in black and white. Ridiculous.

 

“Colour vision was highly developed by the Jurassic Era. The early mammals had lost colour vision because they were nocturnal. When the dinosaurs were wiped out and daytime niches opened for the mammals to take over, colour vision evolved again from mutations in the mammals’ rod pigment. This can be deduced by the genetics of the pigments. However, mammals never got further than 3 color pigments, and poor performers at that. The red and green pigments are too close together, the green and blue too far apart and the blue misses out on long wavelength ultraviolet that non-mammalians can see. Even insects put us to shame in the colour perception department. Birds have 4 colour pigment, with a much better spread than our 3:

 

human vs animal vision

“In addition, some birds and insects can see the polarisation of light. This is an aid to navigation since polarization penetrates clouds dense enough to blot out the location of the sun.

 

“In summary, I think Scott’s position should be adopted. The club went to significant expense in building a wheel chair ramp to make the observatory disabled accessible We should install accessible orange lighting as well.”

 

Thanks for taking the time and effort to research this, Bruce! We’ll make every effort to make this lighting system functional for everyone.

 

Clear Skies, Charles Ennis, President.

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