Hello Halos: Why Some Christmas Lights Seem to Glow

by MikeMeehan 12/22/2016 9:31 AM

If you’re anything like my family, you’ll hop into a car this holiday season, and cruise the neighborhood to view Christmas lights. Who knows? Maybe a house will have decked its walls with a synchronized display to the Trans-Siberian Orchestra’s “Wizards in Winter.” Or maybe it’s not as elaborate. In either case, Christmas lights emit some of the magic of the holidays. Sometimes, usually on an older string of lights — those fat nine-watt incandescent bulbs — you’ll see a halo around the light. What causes that halo? Two Types of “Fractions” that Produce Halos To best understand the halo effect, let’s start with two types of “fractions”: refraction and diffraction. Both definitions involve light traveling through matter. Refraction In refraction, light passes through matter and is knocked off course, so it travels indirectly from Point A to Point B. This is what happens with 22-degree halos, which are the most common halos to form around the sun or moon. The light from the sun encounters ice crystals in the air, and the light is knocked off course, forming a halo around the sun or moon. Diffraction With diffraction, the light passes through a narrow aperture and spreads out. Imagine a camera. The camera has an aperture, which determines how much light will enter into the lens. If more light tries to come in than the lens allows, the light will bend around the edges. When light bends around the edges, it can cause interference between the light waves, producing a halo effect. But this doesn’t just happen with cameras. This can happen with our eyes too. Our pupils determine how much light comes in. If it’s dark, they dilate, and if it’s light, they shrink. After the light enters the pupil, it interacts with the lens: a round and flat part of the eye right behind the pupil. Seeing the Lights When we look at Christmas lights, our eyes take in a certain amount of light, and the rest bends around the edges of our pupils. Unfortunately, the halo effect in Christmas lights is becoming a thing of the past. LED lights are starting to replace the old two-inch bulbs. These are more energy efficient, so they don’t put out as much light. Light probably won’t bend as much around the edges of your pupils, thus diminishing the chance of the halo. As you look at lights this holiday, and as you remember the reason for the season, remember that your eyes let you see the world. So you’ll want to take good care of them. One simple way is by scheduling regular checkups with your optometrist. This holiday, celebrate friends and family, and be thankful for your eyes!  

What to expect during an eye exam

by MikeMeehan 8/26/2016 4:25 PM

Have you been putting off getting an eye exam? August is National Eye Exam Month, making it the perfect time to take charge of your vision health. Even if your vision seems fine to you, eye exams can identify potential problems and serious threats, like glaucoma and cataracts, before they get out of hand. During a comprehensive eye exam, your doctor will exam both the inside and outside of your eyes through a series of tests. Sharpness and clarity Visual acuity tests measure the sharpness and clarity of your vision. The doctor will test how well you can see objects, from a distance and up close, by having you identify the smallest line of letters you can read clearly on an eye chart. Cover test How well your eyes work together is measured using the cover test. The doctor will have you stare at a distant object in the room while having you cover each eye alternately. You’ll repeat the test focusing on an object close to you. The doctor uses these tests to assess whether the uncovered eye must move to focus on the target. Ocular mobility To evaluate how well your eyes can follow a moving object and move between two separate objects, your doctor will conduct two tests. The doctor will have you follow the movement of a small light or other target with just your eyes. You’ll then be asked to focus on one object and move your eyes to another to test how well your eyes move between the two objects. Retinoscopy Early on in your examination, the doctor measures the eyes’ refraction using a retinoscope. The doctor shines a beam of light in the eye, then places a series of lenses in front of the eye, and observes the reflection off the retina. The way the light reflects determines if you can see clearly or if you are farsighted, nearsighted or have astigmatism. This test provides the doctor with an estimate of your glasses or contact lense prescription. Refraction The doctor will use an instrument known as a phoropter to develop your final vision prescription. The phoropter is put in front of your eyes, and the doctor shows you a series of lenses. You can identify the ones that make your vision the sharpest. Eye pressure Two tests can be used to check the fluid pressure of the eyes to see if it is in normal range: the “puff test,” or an applanation tonometer test. During the “puff test” the doctor uses a non-contact tonometer (NCT) to gently push a puff of air onto the eye. Or the doctor may put numbing drops in the eyes and touch the surface of each eye with an applanation tonometer. These tests can help identify glaucoma, a pressure buildup in the eye, which can damage the optic nerve over time and cause vision loss. Pupil dilation The last step in a comprehensive eye exam is to dilate the pupil. In this test, known as the dilated fundus exam, eye drops are put into the eyes to increase the size of the pupil. The doctor uses a slit lamp and biomicroscope to examine the internal areas of the eye, including the optic nerve, blood vessels, retina, vitreous and macula. Pupils may remain dilated for three to four hours after this test. It typically takes 30 minutes to an hour to complete a comprehensive eye exam. Your doctor may also offer you optional tests, such as photographing the eye, which may not be covered by your insurance. After the exam, your doctor will discuss with you any corrective measures you may need and work with you to choose the method that best fits your lifestyle. Whether you need corrective measures or not, the doctor will recommend a date for your next exam.


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