Dim White at Night

Red Night Lights a “Sci­en­tific Blun­der”

Passage Maker - - Postscript -

For pro­fes­sional rea­sons I be­long to sev­eral boat­ing groups on Face­book. One of them—a sail­ing and cruis­ing group—has an el­e­ment gen­er­ally lack­ing in the oth­ers, a sur­feit of ig­no­ra­muses and pi­rate wannabees. Al­though I’ve been sub­merged in the trawler world for 15 years, I’m still a sailor, too, and I own a 41-foot ketch. I al­ways thought sailors were the com­pe­tent, thought­ful ones on the wa­ter. Not so much nowa­days ap­par­ently, as I re­cently found dur­ing an on­line dis­cus­sion of night vi­sion.

Night vi­sion, other­wise known as “dark adap­ta­tion” has been an in­ter­est of mine ever since the Ranger sergeants staged a demon­stra­tion show­ing one of their col­leagues smok­ing a cig­a­rette on a black­ened ridge­line a mile away. Night vi­sion was of ob­vi­ous im­por­tance as I be­gan mak­ing night pas­sages more than 40 years ago. So when some­one polled the Face­book sail­ing group about which color lights were best for night run­ning, I fol­lowed the com­ments thread with in­ter­est.

Nearly all re­spon­ders en­dorsed red light­ing, which is un­der­stand­able since the ma­rine in­dus­try has been mar­ket­ing red light­ing as a way to pre­serve night vi­sion since World War II. The re­spon­ders were un­aware that “rig for red” has been de­moted from best prac­tice to “bet­ter than noth­ing.” Dr. Anita Roth­blum, a U.S. Coast Guard ex­pert on mar­itime ac­ci­dents, called the red light­ing ini­tia­tive on war­ships and sub­marines “a sci­en­tific blun­der” on the part of World War II ex­perts.

(We have posted her 2002 pa­per on the sub­ject, coau­thored by Dan Wy­att, on our web­site. Visit www.pas­sage­maker.com and en­ter the search terms “Night Vi­sion and Night­time Light­ing for Boaters.”)

RODS AND CONES

In “Night Vi­sion and Night­time Light­ing for Boaters,” Roth­blum writes, “In or­der to see a ship in the dis­tance on a cloudy night, we need our rod vi­sion. But in or­der to read charts and ARPA or (elec­tronic chart­ing) dis­plays, we need our cone vi­sion. And we can’t have both at the same time.”

She ex­plains the ori­gin of red light­ing for night op­er­a­tions: “Around World War II sci­en­tists were try­ing to fig­ure out how to light Navy ships and sub­marines so that mariners could see well at night. Some­one no­ticed that the rel­a­tive spec­tral sen­si­tiv­ity curve ap­peared to show that rods were al­most in­sen­si­tive to red/or­ange light…whereas cones were still fairly sen­si­tive.….Thus was born the con­cept of “rig for red”: the hy­poth­e­sis was that if we used red light­ing at night, we would be able to read charts and still pro­tect our sen­si­tiv­ity in the dark. Un­for­tu­nately, this is not the case...”

As Roth­blum notes, “Red text on a white back­ground–eas­ily read­able un­der white light–may ap­pear uni­formly red (and there­fore un­read­able) un­der red light, be­cause they both re­flect red light equally well. Thus, it is im­pos­si­ble to read color-coded charts and dis­plays ac­cu­rately un­der red il­lu­mi­na­tion.”

In ad­di­tion to caus­ing eye fa­tigue, mak­ing it harder to fo­cus, red light­ing may also have a neg­a­tive psy­cho­log­i­cal ef­fect, es­pe­cially when a sit­u­a­tion is stress­ful, ac­cord­ing to Roth­blum.

Roth­blum’s pa­per was in­formed by mid-1980s re­search at the U.S. Naval Sub­ma­rine Med­i­cal Re­search Lab­o­ra­tory, which con­cluded that dim white light was prefer­able at sea. Ma­jor navies are switch­ing to dimmable white (and now green or blue, too) light­ing for night op­er­a­tions, and the rest of us should con­sider do­ing the same. Roth­blum con­curs, not­ing: “Re­cre­ational and com­mer­cial mariners should con­sider the ad­van­tages of us­ing low-level white light on the bridge at night…When charts and dis­plays need to be viewed, low-level white light­ing greatly sur­passes red light­ing in sup­port­ing good color dis­crim­i­na­tion and, there­fore, ac­cu­rate read­ing of charts and dis­plays.”

LOW-TECH SO­LU­TION

Roth­blum also of­fers a quaint sug­ges­tion for im­prov­ing night vi­sion—and it’s one that might ap­peal to the pi­rate wannabees in the Face­book sail­ing group. “The two eyes adapt in­de­pen­dently of each other,” she writes. “To main­tain the great­est de­gree of dark adap­ta­tion, one can place a black patch over one eye be­fore turn­ing on lights to read charts and dis­plays.”

Roth­blum ex­plains the sci­ence be­hind this seem­ingly fan­ci­ful sug­ges­tion: “The patched eye will re­tain its level of dark adap­ta­tion (if lit­tle or no light leaks un­der the patch), while the un­patched eye can read the charts. When the lights are turned off again, take the eye patch off.

The eye that was ex­posed to the light will need time to read­just to the dark. How­ever, the eye that was patched will al­ready be at or near its peak sen­si­tiv­ity.”

This just hap­pens to be one of the the­o­ries be­hind the many por­tray­als of pi­rates wear­ing eye patches. Pi­rates may have worn eye patches just as Roth­blum sug­gested: to pre­serve night vi­sion as they moved from lighted to un­lighted parts of their ships or en­gaged in night fight­ing.

Pre­sented with the de­tailed ev­i­dence by some of the world’s lead­ing ex­perts on the topic, thought­ful sailors might be ex­pected to re­act by say­ing, “Hey, wow! I never knew that.” But no. Sev­eral Face­book­ers con­tin­ued to ad­vo­cate for red be­cause (I guess) their 1980 Hunter 36 came with a red bulb over the nav sta­tion and an­other over the com­pass.

Red night light­ing is not go­ing to kill you. You’ll be fine hold­ing a course with red over your Ritchie. But please, Cap­tain Spar­row, don’t in­sist it’s a best prac­tice with­out re­view­ing the ev­i­dence.

In the next is­sue, I’ll ex­am­ine how mod­ern elec­tron­ics have com­pli­cated dark adap­ta­tion and dis­cuss an ini­tia­tive that could some­day pro­vide relief.

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This is the com­bat in­for­ma­tion cen­ter on a U.S. Navy ship, bathed in blueish light. And al­though th­ese sailors in the be­lowdecks CIC would not be ex­pected to go out­side and scan the hori­zon for other ship­ping, the im­age does demon­strate the cur­rent light­ing prac­tices.

“Rig for red” has be­come “Bet­ter than noth­ing”

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