Astronomy

How close would an LED have to be to your eyes to be as bright as the looking at the sun during midday?

How close would an LED have to be to your eyes to be as bright as the looking at the sun during midday?


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I wonder if it is possible to have an LED screen bright enough to simulate the brightness of our sun from Earth, and if so if it could be made small enough to fit on a laptop screen.


Typical sunlight has a power of a few hundred watt per square meter. A typical laptop screen has a power of about 4-5 watt. So obviously there is a vast difference in how bright they are.

To turn this into an astronomy question we can use magnitudes to answer it. The sun has apparent magnitude −26.7. A laptop at an arms length is about 50 lux, which would be about -18.4 apparent magnitude. So to get a solar apparent magnitude I need it to be 8.25 magnitudes brighter. That corresponds to a brightness increase of $100^{8.25/5}approx 1995$. So if each pixel shone about 2000 times brighter, you would feel like the screen produced sunlight.

You could of course try looking at the screen more closely, making it brighter that way. However, the $1/r^2$ law for how brightness changes with distance stops being valid when your eye get closer to the pixel than the pixel lateral size. Worse, the amount of photons your eye can receive will also be limited by your pupil aperture: you cannot see all of the screen light. So this is why pushing your face against a screen doesn't make it feel like the sun (trust me, I tried this right now with my screen and some sample sunlight).

If it is a smaller region that is very bright surrounded by black it may feel brighter: good visual design can often fake a bit of extra brightness that is not physically there.

I don't see a physical reason for true sunlight intensity screens being impossible, but they are not practical. They would drain batteries like crazy. A visually convincing spectrum may still be doable with less power than a full blackbody spectrum (that would also emit a lot of infrared - nice feeling on the skin, but would heat up the screen a lot) just like LEDs faking white light with just a few frequencies.


With pandemic's wane, open your eyes to whatever 'Wows' you

Hunched over the telescope, I worked on a pencil sketch of Saturn. To ease a stiffening neck, I straightened in the chair and tilted my head back to the sky. At that instant a brilliant fireball meteor flashed across the constellation Hercules — intense blue-green, as bright as planet Venus, leaving a luminous trail.

I've schooled myself to count "one-thousand-one, one-thousand-two …" whenever I see a fireball, so I noted that after three seconds — a long time for a shooting star — its color blazed into orange and the meteor exploded (silently) into four or five fragments that fanned out in a 90-degree arc, each one leaving a faint yellow track for about a second. It's called a bolide ("bowl-eyed"), and I was dazzled.

The bolide — so bright and dynamic — seemed "right there," no higher than an airplane level. But any meteor you see is 50 to 120 miles away. The open-ended sky, stretching from the tip of your nose to eternity — is difficult to fathom, literally. But it's enchanting to try.

When I was 13 my friend John received an inexpensive reflecting telescope for his birthday — essentially a toy. The first clear night he invited me next door to look at the moon. He bent to the eyepiece and I saw him stiffen. "Wow!"

The craters, mountains and "seas" were "right there," more vivid than any picture of the lunar surface I'd ever seen. No other eye, no camera, no photographic emulsion mediated the image. Astronomer Robert Burnham wrote, "The amateur astronomer has access at all times to the original objects of study … as much as do the great observatories of the world." The magnified moon was like a spotlight to the brain. Beautiful, yes, but even more affecting was the signature of the light, a sense of being tethered to the moon. As John edged in for a second look, I made two-footed hops, excited and eager to get back to the eyepiece — a lunatic, awakened by moon gleam.

In August 1994 I was on a crew working a major forest fire in north-central Idaho. It was exhausting labor, and by the end shift we were primed for a hot supper and the snug cocoons of our sleeping bags. But at nightfall I was distracted. Our camp was in a mountain meadow at 6,500 feet elevation. The murkiest layer of our planet's atmosphere puddled far below. The Milky Way was luxuriant, like a sun-drenched cloud. Individual stars were flinty points of brilliance. Each night I strolled beyond the pool of lantern light into the radiance of the galaxy.

One evening I was trailed by Y.T., a combat-hardened Vietnam veteran who had related horrifying tales about the war. He was minus a kneecap that had been shot away in a firefight. Y.T. had seen and comprehended much, but not the night sky, not like this. He asked what I was looking at. I pointed. There was the Andromeda Galaxy, over 2 million light years distant, but it's oval shape apparent to the naked eye. I mentioned that due to the finite velocity of light, the image we were seeing was 2 million years old.

There was Polaris, the north star. It's height above the horizon in degrees indicated our latitude. I explained the nature of the Earth's rotation. There, just rising over a mountain peak was the star cluster Pleiades — the Seven Sisters — a stunning shoal of sapphires. And dominating all, the Milky Way itself, an effulgent tide of stardust and suns.

I explained it was the disk of our own spiral galaxy, spread across a hundred thousand light years from the center that we could see before us in the constellation Sagittarius. And when we gazed in the other direction, out of our galaxy toward Andromeda, we were peering into the chasm of intergalactic space at another spiral even bigger than our own.

Y.T. slowly sank into the frosty grass, favoring the leg without a kneecap. He laid back and swept his eyes from horizon to horizon.

"But …" he whispered, "but …" A long pause. "Wow."

His face, despite its weathered creases, was childlike. He blinked and gazed. His lips parted and he mouthed a second, silent "wow."

He was seized by revelation, warmed by astronomical happiness — a joy in the presence of celestial splendor reverence at the altar of sheer magnitude wonder at locating oneself in a cosmic perspective. Best of all, it's a brief passage beyond that self.

We are needy, self-absorbed biological creatures whose fundamental instincts are for survival and propagation. Any time we can transcend the tyranny of our genes is precious, and the night sky is a portal to transcendence. The stars say "get real," notice the scope of the universe. Our everyday concerns are not trivial, but assign them a cosmic dimension — for a little while at least. We are infinitesimal motes, yet our minds can encompass the galaxy and imagine the universe beyond.

I've not seen Y.T. again, but a few months after our tour of duty I received a letter. He recalled our night stroll and said he was now learning the constellations with his kids. He wrote, "It was a great gift you gave me, man."

During the past year of uncertainty and fear — pummeled by pandemic and politics — I often found solace in the night sky, blessed with the opulent darkness of the North Woods. I felt sorry for anyone cooped up in a metropolis, caged within the murky toxicity of artificial light. I relished the loveliness and repeatedly reconnected with the heavenly perspective: This too shall pass.

The pandemic year, while special, was a mere reminder that we always require solace, and of course it need not be astronomy. Any number of passions and pursuits will suffice.

In his novel "The Once and Future King," T.H. White channels a famous wizard: " 'The best thing for being sad,' replied Merlyn, beginning to puff and blow, 'is to learn something. That is the only thing that never fails. You may grow old and trembling in your anatomies, you may lie awake at night listening to the disorder of your veins, you may miss your only love, you may see the world about you devastated by evil lunatics, or know your honor trampled in the sewers of baser minds. There is only one thing for it then — to learn. Learn why the world wags and what wags it. That is the only thing the mind can never exhaust, never alienate, never be tortured by, never fear or distrust, and never dream of regretting.' "

The implicit caveat is that whatever you seek to know should have tangible connections to reality. In our era of internet idiocies vigilance is paramount, but there still exists a plain route to whatever truth we humans can discern.

And like any great hunt, the chase should bring joy. If your learning doesn't generate some gladness and contentment, you may be on the wrong track.

Peter M. Leschak, of Side Lake, Minn., is author of "Ghosts of the Fireground" and other books.


Make some simple changes to:

Your computer screen:

  • Place it 20-26 inches away from your eyes and a little below eye level.
  • Regularly clean off dust and fingerprints from the surface. Smudges can reduce contrast and create problems like glare and reflections.
  • Choose screens that tilt and swivel.
  • Use a glare filter for your screen.

Your work environment:

  • Change lighting to get rid of glare and harsh reflections.
  • Use an adjustable chair.
  • Place a document holder next to your computer screen.

Your work habits:

  • Try the 20-20-20 rule. Every 20 minutes, look at something about 20 feet away for 20 seconds.
  • Post a note that says "Blink" on your computer as a reminder.
  • Take regular breaks from computer work.

Your eye-care routine:

  • Apply a washcloth soaked in warm water to tired, dry eyes (keep your eyes closed).
  • Use artificial tears to refresh your eyes when they feel dry.
  • To help prevent dry eyes while indoors, use an air cleaner to filter dust and a humidifier to add moisture to the air.

If you have eye fatigue or pain, see an eye doctor to make sure a deeper medical condition isn’t to blame.

If the problem doesn’t go away, make an appointment for a full eye exam. The doctor can make sure your symptoms aren’t linked to a problem like an eye muscle imbalance or dry eye. They can also tell if your glasses or contact lens prescription is up to date and good for computer use.


If you can’t have sunlight, mimic sunlight

If you can’t get sunshine inside your gym, you should have one overarching goal: To use lighting that is as close to sunlight as possible in amount, direction, and color. In other words, lots of light, coming from above our heads, and as close to the color of sunshine as possible.

That means no fluorescent lights. Those old school shop lights or cheap lighting ballasts aren’t the best choice and can be quite harsh on your eyes. Fluorescents tend to flicker and buzzz. They have a short lifespan and are not very efficient. They aren’t even the right color temperature. In other words, they are most definitely not like sunlight!

Instead, if you can, use LED lighting. It will often be the most flexible and cost effective. Today’s lighting choices are rife with LED options and you will have a ton of lights to pick from. The right LED lighting can be very close to actual sunlight and will almost always be your best option.

A primary benefit of LED lights is a choice in color temperature. Make sure to choose lighting that is classified as “daylight” in color or has a listed color temperature of 5000k. 5000k is the same color temperature as the midday sun.

You will often see “soft white” as an option. Stay away from this for your gym. Matching the color temperature of the lighting to that of the sun will add energy to both you and your space. It will be easy on your eyes and it will provide a pleasant atmosphere to train in.

Just like the sun, you want your lighting overhead. Hang it from or recess it into the ceiling. Get it up and out of your way. You will be especially thankful for this if you have mirrors in your gym. Overhead lighting will be more flattering than light that comes from most other directions. It will also eliminate unwanted reflections if you have mirrors mounted in your gym.


6 Things to Avoid While Looking at the Supermoon

On November 12 and 13, the Moon will be full and near its perigee, or its closest orbital approach to Planet Earth, a combination that has recently entered public awareness as a “supermoon.” During a “supermoon” the full moon appears slightly larger than usual: at its closest approach to Earth, the full moon looks around seven percent wider than average.

Sound anticlimactic? It is, a little. But the term “Slightly Larger Than Average Moon” probably wouldn’t generate as many page views for the astrology sites that came up with the term.

That’s right: the Supermoon idea originated among astrologers, not astronomers. As astrologer Richard Nolle originally coined it in 1979, the term “Supermoon” originally meant either a full or a new moon at its closest approach to Earth. If you asked an astronomer to come up with a term for that set of conditions, she’d probably call it something long the lines of “perigee-syzygy.“ “Perigee” as we said above, is the Moon’s closest approach to Earth “syzygy” is when three or more astronomical objects are roughly lined up, which happens during every full or new moon.

Aside from eclipses of either the sun or moon, which happen only when the Sun, Earth, and Moon are in syzygy, or transits of the sun, when another planet lines up between the Earth and Sun, astronomers generally only get excited about syzygy when they have an opportunity to use it in Scrabble, especially if a triple word score tile is involved. In astrology, contrariwise, a supermoon is apparently a big deal.

But you don’t have to care about astrology to appreciate a bigger-than-usual full moon. All you need is a good place to park yourself on the Earth’s surface.

Moderately good vision is a plus, of course, and you can boost whatever vision you have with lenses, ranging from army surplus binoculars to telescopes with price tags as astronomical as the heavenly bodies at which you point them.

We’ve taken care of the first part for you, with our list of 64 southern California stargazing sites. Use the map to find a site close to you, check out our listing for the site, and see if it might not be a worthwhile place for supermoon viewing.

Once you get there, you may find you have even the most popular stargazing sites all to yourself. A big bright full moon interferes with viewing other heavenly bodies, just by washing out the sky a little. But you might find yourself joining a moon-gazing crowd instead. And as with any pastime, there are mistakes beginners can make that can interfere with your enjoyment, or the enjoyment of others nearby. With stargazing in particular, there are a couple bad practices that can actually cause significant damage to expensive equipment, or even personal injury.

So here are some Best Stargazing Practices for you to keep in mind whether you’re heading out to enjoy the Supermoon, or planning a trip two weeks after to explore the dark, moonless skies of Southern California.

Be careful to protect people’s night vision.

Human eyes take some time to adjust to darkness: it can be as long as half an hour after exposure to bright light before our irises relax to full light-admitting mode. Stargazers rely on night vision to spot stars, planets, and other astronomical objects. Even when looking at a bright full moon, night vision can allow the observer to pick out fine detail through a telescope that might be lost to someone who just got out of a brightly lit room.

Avid stargazers know that red light interferes less with night vision, and specialty stores and websites sell red flashlight lenses for just this purpose: to allow people to use see where they’re going without blinding everyone at the star party.

Even if you don’t shell out for a red lens, you can protect your night vision and that of those around you by refraining from using a flashlight, or pointing it directly at the ground if you absolutely need to use it. When approaching a stargazing site in a car, be mindful of where you point your headlights. Especially don’t point them in the direction of the telescopes and then leave them on as you rummage through the back seat for your water bottle.

And don’t expect to be able to use a headlamp at a star party. You know, the kind that sits on your forehead, blinding everyone who faces you directly? Just don’t.

The same goes for other forms of illumination. I was at a star party some years ago where a novice eagerly showed off the star map app on his phone, pushing it into the faces of everyone else there on one occasion or another. His screen was bright, and there was much ill-tempered grumbling at his inadvertent sabotage of people’s night vision. Some apps have a red mode to lessen the damage, which is helpful. But that help may be negated by the screens you have to navigate through to get to the app. Consider saving smartphone app use for afterward.

Meanwhile, stargazers in the know who need to use laptops or tablets for stargazing notes on a regular basis will often bring a thick beachtowel or similar cloth shield to keep from inflicting night vision damage on others around them.

Leave the laser pointers at home

This is related to the night blindness issue, but with the added possibility of actual permanent vision damage. Some experienced star party leaders will use laser pointers to direct people’s attention to a particular part of the night sky. The beam illuminates dust particles along its path, providing a visual aid much more helpful than pointing a finger in total darkness.

But laser pointers can cause eye damage even to people in brightly lit rooms. When your irises are fully dilated and allow more light in, that damage can be even worse. People who’ve led stargazing events for some time develop reflexes that help them avoid accidentally pointing their lasers in your face. Unless you’re practiced, you’re better off not bringing that pointer along.

At least not without asking the owners of any nearby optics. Your cigarette smoke can leave a layer of oil and dust on lenses that can be hard to clean off. Same goes for campfires, which can also pollute the night with bright light. At least walk away a few hundred feet before lighting up. And that goes for smokables other than just tobacco.

Use your stargazing voice

You know that thing when you’re driving in a dark neighborhood listening to loudish music and looking for a particular address, and most of the houses’ street numbers are hard to make out, and so you turn the radio down so you can see better? Noise can make it difficult to focus when you’re trying to observe faint, dim objects. Speaking in quiet tones will help other people get more out of their stargazing.

Obviously, if your supermoon viewing party is taking place in your backyard and the invites you sent out specifically mentioned alcohol and hollering as planned activities, this one doesn’t necessarily apply. But at organized events not in your yard, plan to spend the evening without amplified music, loud shouting, or bullhorn use.

Leave your rambunctiousness at home

It’s dark out. You’re in somewhat unfamiliar surroundings. The footing might be uncertain. There are large tubes of glass and mirrors standing atop tripods, some of them connected to power sources or nearby computers by means of dark cables. Some of those assemblages of telescopes, tripods, and cables cost tens of thousands of dollars. Some of them are sturdy enough that they’ll injure you if you run into them.

If you’re in the company of other stargazers whom you’ve just met, expect to move slowly and methodically among them to avoid embarrassing and potentially expensive mishaps.

And while you should by all means introduce any children to which you may have access to the practice of stargazing, keep their level of impatience, fatigue, frustration, and poor impulse control in mind as the night progresses.

And leave your dog at home, probably.

One last “don’t” before we get to the “do”s:

Don’t twiddle the knobs without asking

People who sink lots of money into amateur astronomy gear are often eager to share what it reveals with stargazing BFFs, even if you're a BFF they met just 10 minutes ago. They’re also going to be a whole lot better at adjusting their equipment for clear viewing than you are. If you’re invited to look through someone else’s scope, resist the temptation to adjust the focus without asking. Chances are, if they’re letting you look through their scope, they’ll be happy to adjust it for you.

And now the things you absolutely SHOULD do:

Whether it’s basic questions like “what am I supposed to be seeing in this scope” and “why does the moon look upside down in this viewfinder,” or more specific questions about the distance and size of stars, nebulae, and planets you’re viewing, ask those questions. Don’t be shy. The amateur astronomer community values education, and people wouldn’t organize star parties if they didn’t want to answer questions. If you’re not at a planned event but inadvertently near a group of stargazers, the same might well hold true, especially if they strike up conversation or invite you to look through their scopes.

Because let’s face it: those of us who avidly pursue stargazing include a very high percentage of nerds relative to the community at large, and there’s nothing we nerds like more than fielding questions we know the answers to. Except sometimes for fielding questions we realize we don't know the answers to.

DO bring along friends who haven’t stargazed before

Whether it’s to look at a “supermoon,” watch rocks fall out of the sky during one of this planet’s seven major annual meteor showers, or to admire the glory of the increasingly unfamiliar Milky Way from an especially dark place, looking at the sky is an increasingly rare pastime — ironic, given that almost every member of our species used to do it on a daily basis. More people who enjoy stargazing means more people willing to advocate for dark skies. And you may just introduce your friend to something that will become a life-long passion.

DO go out and look at the sky even if there’s nothing special going on

Because there’s always something going on. Meteors fall from the sky without checking to see if there’s a shower in process. The dark edge of the moon will slip across the sky, hiding one star after another. Planets move across the field of stars a little each night. The seemingly static constellations swim laps around the calendar: Orion will rise a little earlier each autumn night, his dog Canis Major nipping at his heels.

And even in the brightest parts of Southern California, there are places you can watch it all happen.


Installing accessories

This cut-away diagram is from the Details page and will assist you in understanding the procedure. The procedure is the same for all models.

  • Do not touch the reflective surface of the reflector - the reflective surface cannot be cleaned - touching the reflective surface will damage it. Do not touch the LED - touching the LED will damage it.
  • Unscrew the head from the battery compartment. Set the battery compartment aside.
  • The reflector holds the bezel and head together. When you unscrew the bezel from the head, the reflector normally stays with the bezel. However, sometimes the reflector will stay with the head. The procedure changes depending on which circumstance happens.
  • Reflector stays with the head. Put the head on the table reflector up. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the head on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the head, reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
  • Reflector stays with the bezel. Set the head aside, LED side up. Using a strap wrench, unscrew the reflector from the bezel until the O-ring is exposed and stop there - you should now be able to use your fingers to finish unscrewing the reflector. Put the bezel/reflector assembly bezel up on the table - i.e., it will be sitting on the flat end of the reflector. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the reflector on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
  • If the upper O-ring is not on the lens, carefully remove it from the bezel and set it on the lens directly above the lower O-ring.
  • Carefully place the new bezel over the stack and screw it down. Ensure that the O-rings sit in their little grooves and do not come out and get pinched. If the reflector stayed with the bezel during disassembly, lift the stack off the table keeping it in the same orientation and place it on the head and screw the reflector into the head. Tighten everything by grabbing the bezel and head. You only need to tighten until the gaps between the bezel, reflector and head are gone - do not over tighten.

This cut-away diagram is from the Details page and will assist you in understanding the procedure. The procedure is the same for all models.

  • Do not touch the reflective surface of the reflector - the reflective surface cannot be cleaned - touching the reflective surface will damage it. Do not touch the LED - touching the LED will damage it.
  • Unscrew the head from the battery compartment. Set the battery compartment aside.
  • The reflector holds the bezel and head together. When you unscrew the bezel from the head, the reflector normally stays with the bezel. However, sometimes the reflector will stay with the head. The procedure changes depending on which circumstance happens.
  • Reflector stays with the head. Put the head on the table reflector up. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the head on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up and set it aside. You should be left with the head, reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
  • Reflector stays with the bezel. Set the head aside, LED side up. Using a strap wrench, unscrew the reflector from the bezel until the O-ring is exposed and stop there - you should now be able to use your fingers to finish unscrewing the reflector. Put the bezel/reflector assembly bezel up on the table - i.e., it will be sitting on the flat end of the reflector. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the reflector on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up and set it aside. You should be left with the reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
  • If the upper O-ring is not on the lens, carefully remove it from the bezel and set it aside. If the upper O-ring is on the lens, carefully pick it up and set it aside.
  • Pick up the lens. If the lower O-ring sticks to the lens, remove it and carefully set it back on the reflector in the O-ring groove. Set the lens aside.
  • Set the new lens centered over the reflector and lower O-ring. Verify the lower O-ring is seated in the O-ring groove.
  • Place the upper O-ring on the lens directly above the lower O-ring.
  • Carefully place the bezel over the stack and screw it down. Ensure that the O-rings sit in their little grooves and do not come out and get pinched. If the reflector stayed with the bezel during disassembly, lift the stack off the table keeping it in the same orientation and place it on the head and screw the reflector into the head. Tighten everything by grabbing the bezel and head. You only need to tighten until the gaps between the bezel, reflector and head are gone - do not over tighten.

How do I swap reflectors?

This cut-away diagram is from the Details page and will assist you in understanding the procedure. The procedure is the same for all models.

  • Do not touch the reflective surface of the reflector - the reflective surface cannot be cleaned - touching the reflective surface will damage it. Do not touch the LED - touching the LED will damage it.
  • Unscrew the head from the battery compartment. Set the battery compartment aside.
  • The reflector holds the bezel and head together. When you unscrew the bezel from the head, the reflector normally stays with the bezel. However, sometimes the reflector will stay with the head. The procedure changes depending on which circumstance happens.
  • Reflector stays with the head.
    • Put the head on the table reflector up. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the head on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the head, reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
    • If the upper O-ring stayed with the bezel, gently remove the O-ring from the bezel and set it aside. If the upper O-ring stayed with the lens, carefully pick it up off of the lens and set it aside. Set the bezel aside.
    • Remove the lens from the stack and set it aside. Remove the lower O-ring from the stack and set it aside.
    • Use a strap wrench to remove the reflector. Set the old reflector aside. Leave the head sitting on the table LED side up.
    • Set the head aside, LED side up.
    • Using a strap wrench, unscrew reflector from the bezel until the O-ring is exposed and stop there - you should now be able to use your fingers to finish unscrewing the reflector. Put the bezel/reflector assembly bezel up on the table - i.e., it will be sitting on the flat end of the reflector. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the reflector on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
    • If the upper O-ring stayed with the bezel, gently remove the O-ring from the bezel and set it aside. If the upper O-ring stayed with the lens, carefully pick it up off of the lens and set it aside. Set the bezel aside.
    • Remove the lens from the stack and set it aside. Remove the lower O-ring from the stack and set it aside. Set the old reflector aside.

    How do I swap buttons?

    NOTE: You cannot swap buttons on the rotary control - only on Clicky style switch caps. This procedure only applies to the newer Acme-thread battery compartments and the Rev 3 version of the older V-thread battery compartments. Older battery compartments do not have user-replaceable buttons. The procedure is the same for raised and flush buttons.

    This cut-away diagram is from the Details page and will assist you in understanding the procedure.

    • Unscrew the switch cap and set the rest of the flashlight aside.
    • Using an appropriately sized coin or pin wrench, unscrew the button retainer.
    • Remove the old button and insert the new button. Be sure the new button is centered in the switch cap.
    • Apply a small amount of grease to the back side of the button retainer. This will ensure it can slide over the rubber button without grabbing the rubber.
    • Screw in the button retainer until there is a hard stop - i.e., the button retainer bottoms. Do not over tighten the button retainer.
    • Screw the switch cap back on the flashlight.

    How do I install the universal pocket clip and lanyard attachment?

    The universal pocket clip and lanyard attachment will fit all models of our flashlights. The universal pocket clip can be installed on the switch cap to allow bezel down carry of your flashlight. The universal pocket clip can be installed on the head to allow bezel up carry of your flashlight. With the bezel up orientation, the flashlight may be clipped to a hat for hands free use. Finally, a lanyard may be attached to the lanyard loop - the U bend in the clip.

    Your universal pocket clip and lanyard attachment comes with a #0 Phillips screw driver, which is needed for installation.

    Follow these steps to install your universal packet clip:

    • Loosen all three screws. The two outer screws only need to be loosened half a turn. The center screw should be loosened so the head of the screw is at the same height as the two outer screws.
    • Slide the ring over the flashlight. For bezel down orientation, the ring will be over the switch cap and the lanyard loop on the clip should be flush with the end of the switch cap. For bezel up orientation, the ring will be over the head.
    • Hold the clip in position and tighten the two outer screws.
    • Continuing to hold the clip in position, tighten the center screw. The clip should be completely snug.

    The installation is now complete. You reverse the procedure to remove the universal pocket clip and lanyard attachment.

    Note: the center screw is slightly longer than the outer two screws. If the wrong screw is in the wrong hole, the clip will remain loose even with the screws tight. The two shorter outside screws are 0-80 x 1/8&rdquo pan head Phillips. The longer center screw is a 0-80 x 5/32&rdquo pan head Phillips.

    How do I install the Clicky-style pocket clip?

    The Clicky-style pocket clip for the EDC Executive and EDC LE flashlights installs between the battery tube and the switch cap in a groove between the two items.

    This cut-away diagram is from the Details page and will assist you in understanding the procedure.

    Follow these steps to install your Clicky-style packet clip:

    • Unscrew the switch cap and set the switch cap aside.
    • If the external O-ring was installed, remove it and set it aside. The external O-ring was visible prior to removing the switch cap and is visibly narrower than the internal O-ring. The external O-ring is not used when the Clicky-style pocket clip is installed.
    • Remove the internal O-Ring and set it aside. The internal O-ring sits in a groove just past the threads. It is visibly fatter and slightly smaller in diameter than the optional external O-ring. Be careful not to damage this O-ring because it seals the switch cap.
    • Slide the pocket clip over the threads, past the groove and onto the narrow shelf just past the O-ring groove. You will need to hold the pocket clip in this position temporarily.
    • Replace the interior O-ring into its groove between the pocket clip and the threads.
    • Replace the switch cap. The switch cap can be tightened against the pocket clip to keep the pocket clip securely in one position.

    The installation is now complete. You reverse the procedure to remove the Clicky-style pocket clip.

    You may want to save the optional external O-ring if you later remove the pocket clip - to provide a nicer exterior appearance. However, the optional external O-ring is not necessary and may be thrown away.

    How do I install the external Clicky switch cap O-ring?

    When the Clicky pocket clip is not installed, there is a gap between the battery tube and the switch cap. The purpose of the external O-ring is to provide a nicer exterior appearance by filling in the gap. The external O-ring is optional and has no effect on the operation of the flashlight - it is not required.

    The external O-ring is installed by rolling it over the Clicky switch cap and into the gap between the battery tube and the switch cap.

    The groove width can be adjusted by loosening or tightening the Clicky switch cap slightly, and should be adjusted to be large enough to allow the O-ring to sit down into the groove so it is flush with the outside surface. This provides the best appearance and keeps the O-ring recessed so it will not snag on anything.


    Which Color/Wavelength of Light is Beneficial for eyes?

    Most of the studies that point to beneficial effects use LEDs as the light source with the vast majority around the wavelength of 670nm (red). Wavelength and light type/source are not the only important factors though, as the light intensity and exposure time affect the results.

    How does red light help the eyes?

    Given that our eyes are the primary light-sensitive tissue in our body, one might think that the absorption of red light by our red cones has something to do with the effects seen in the research. This is not entirely the case.

    The primary theory explaining the effects of red and near infrared light therapy, anywhere in the body, involves the interactions between light and the mitochondria. The core function of mitochondria is to produce energy for its cell – light therapy improves its ability to make energy.

    The eyes of humans, and specifically the cells of the retina, have the highest metabolic requirements of any tissue in the entire body – they require a lot of energy. The only way to meet this high demand is for the cells to house many mitochondria – and so it is no surprise that cells in the eyes have the highest concentration of mitochondria anywhere in the body.

    Seeing as light therapy works via interactions with the mitochondria, and the eyes have the richest source of mitochondria in the body, it is a reasonable assumption to hypothesise that the light will also have the most profound effects in the eyes compared to the rest of the body. On top of that, recent research has shown that degeneration of the eye and retina is directly linked to mitochondrial dysfunction. So a therapy that can potentially restore the mitochondria, of which there are many, in the eye is the perfect approach.

    Best wavelength of light

    670nm light, a deep red visible type of light, is by far the most studied for all eye conditions. Other wavelengths with positive results include 630nm, 780nm, 810nm & 830nm. Laser vs. LEDs – a note Red light from either lasers or LEDs can be used anywhere on the body, although there is one exception for lasers specifically – the eyes. Lasers are NOT suitable for light therapy of the eyes.

    This is due to the parallel/coherent beam property of laser light, which can be focused by the lens of the eye to a tiny point. The entire beam of laser light can enter the eye and all of that energy is concentrated into an intense tiny spot on the retina, giving an extreme power density, and potentially burning/damaging after just a few seconds. LED light projects out at an angle and so does not have this issue.

    Power density & dose

    Red light passes through the eye with over 95% transmission. This is true for near infrared light and similar for other visible light such as blue/green/yellow. Given this high penetration of red light, the eyes only require a similar treatment modality to the skin. Studies use around 50mW/cm2 power density, with quite low doses of 10J/cm2 or less. For more information on light therapy dosing, see this post.


    Photophobia treatment

    The best treatment for light sensitivity is to address the underlying cause. Once the triggering factor is treated, photophobia disappears in many cases.

    If you are taking a medication that causes light sensitivity, talk to your prescribing physician about discontinuing or replacing the drug.

    If you&aposre naturally sensitive to light, avoid bright sunlight and other harsh lighting sources. Wear wide-brimmed hats and sunglasses with ultraviolet (UV) protection when outdoors in daylight. Also, consider wearing eyeglasses with photochromic lenses. These lenses darken automatically outdoors and block 100 percent of the sun&aposs UV rays.

    For bright sunlight, consider polarized sunglasses. These sun lenses provide extra protection against glare-causing reflections of light from water, sand, snow, concrete roadways and other reflective surfaces.

    In an extreme case, you may consider wearing prosthetic contact lenses that are specially colored to look like your own eyes. Prosthetic contact lenses can reduce the amount of light that enters the eye and make your eyes more comfortable.


    Using a SAD lamp

    If you aren’t familiar with bright-light therapy, read up on it before proceeding. The Wikipedia article could be a good starting point.

    There is compelling evidence for efficacy in treating SAD, including mild “winter blues” as well as major clinical depression. It also appears to be effective in treating sleep cycle disorders. (Many SAD sufferers have longer-than–24-hour cycles, resulting in “permanent jetlag.”) There’s also moderate evidence of efficacy for treating non-seasonal depression. Bright light therapy can trigger mania or hypomania, so you may want to consult a doctor.

    What is not clearly known is how light therapy works, and what is the best way of applying it. Unfortunately, this uncertainty has left room for dubious claims and outright pseudoscience, promulgated mainly by makers of devices that probably don’t work at all. The rest of this section treats uncertain issues, based on a combination of my personal experience and reading so it too is not very well-grounded scientifically.

    SAD is basically hibernation. For me, it is not primarily affective. My brain slows down after the equinox, and—without treatment—by December it’s impossible to do serious thinking. I do tend to get depressed in winter, but I suspect that’s mostly because I can’t think properly.

    SAD is probably triggered by visual cues: the length and brightness of the day. Some purported SAD treatments shine light on the skin, not in the eyes I doubt those work.

    From my experience, the more sun-like the light is, the better. It’s better if the light seems to come from the same angle above your eyes as on a summer day it’s better if it is extremely bright it’s better if it is truly white. (More about whiteness below.)

    To simulate a long summer day, light therapy is most effective in the couple of hours before the natural daybreak, and starting at the natural twilight. I turn mine on as soon as I wake up, and as soon as it starts to get dark, and also run it in the middle of the day if it’s gloomy outside. There’s clinical evidence that ramping up the brightness gradually before you wake up (“dawn simulation”) is highly effective. I haven’t tried this. Informally, I do “sunset simulation” by dimming the light gradually in the evening, and also shifting its color toward yellow from white.


    BOTTOM LINE

    Current lens technology is evolving, but at the moment, the limitation of current laser lens technology means situational awareness and broad protection are on opposite sides of the coin. To see everything, you’ll have to give up some protection. Since lasers are still an emerging threat to law enforcement, the defensive technology is still in active development. Researchers are focused on finding a no-compromises solution to laser vision threats that’s practical for line units. We’re getting close but armed with the knowledge in this article, you should be clear on the hows and whys, as well as the compromises needed to make an informed decision when shopping for laser eyepro.



Comments:

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