LED Flashlights and Your Eyes: Why More Lumens isn’t Always Better

LumensA bright LED flashlight can be one of your greatest assets in the wilderness. Used inconsiderately, however, it can also be a huge nuisance to those around you. Because flashlights and headlamps are such an integral part of the outdoor experience, every hiking, camping, hunting and fishing enthusiast can benefit from having a basic understanding of how our eyes interact with the light from an LED flashlight.

The following is a look at how the eye operates, as well as an overview of some of the different functions of LED flashlights and headlamps with eye science in mind. You may just learn a better way to use your LED flashlight on your next outdoor adventure.

A Basic Introduction to How Your Eyes Work

The human eye uses two basic biological structures to see: rods and cones. Cones are located near the center of your field of vision. They generally handle daytime brightness, colors and details. Rods, on the other hand, are located around the edges of the field of vision. (This explains why you can often see objects better at night if you look at them askance, rather than directly.) Rods operate best in low-light conditions and generally provide visual cues in black and white.

Both rods and cones are located on the retina, an extremely sensitive layer of tissue located at the back of the eyeball. The data communicated by rods and cones are translated into electrical impulses, which the brain transforms into an image. Overall, the human eyeball is excellently prepared to operate in both daytime and nighttime situations. However, if you throw an LED flashlight into the mix, it’s easy to destroy your natural night vision, as further explained below.

How LED Flashlights Affect Night Vision

To dive a bit deeper into the biology of vision, consider this: A special biological pigment called rhodopsin aids the eye’s rods in delivering nighttime sight. Rhodopsin molecules actually change shape as light hits them. Extremely bright light shocks rhodopsin molecules into very different shapes. It can take as long as half an hour for the body to return its rhodopsin stores back into the shape that works best for night vision.

For this reason, avid hunters and fishermen hate it when a newbie blasts his or her LED flashlight without warning. Even a moment of LED light can destroy your night vision temporarily.

You may have noticed outdoorsmen favoring red-tinted LED flashlights in night expeditions. There’s a good biological reason for this, as well. Namely, your eye’s rods can’t detect red light. Its cones, however, can. Using an LED flashlight or headlamp on the red setting helps preserve night vision by taking advantage of your cones’ ability to see color. At the same time, red light doesn’t trip the eye’s rods, thus protecting your rhodopsin molecules and preserving natural night vision.

Why More Lumens Isn’t Always Better

Another thing to keep in mind about the human eye is that it can operate at a wide range of brightness levels. In very bright conditions, the pupil closes to restrict the amount of light that enters the eye. In lower light conditions, rods and their rhodopsin take over. The strange thing about the whole sensitive system is that in order to notice a change in brightness, the amount of light must double. In other words, the human eye responds to light in a logarithmic pattern.

This is counter-intuitive; most of us crank the amount of light emitting from our LED flashlights with no sense that less light may actually work better for the task at hand. Blasting the highest level of your flashlight only destroys your night vision. Furthermore, your eyes probably don’t need that much light to operate well. Keeping your LED flashlight at dimmer settings and conservatively adding brightness will both preserve your night vision and maximize your eyesight.

Spot Lights vs. Flood Beams

As explained above, the biology of the human makes it difficult to quickly switch between extremely bright and extremely dark situations. This comes in handy when using an LED flashlight with an adjustable beam.

First, begin with a dimmer light setting than you think you need, then slowly add more light as you need it. Second, a more dispersed light beam may serve your vision better, depending on your purpose. If you want to see something very far away, a focused beam will work well. However, it will be difficult for your eyes to switch from the light of the beam to the surrounding darkness. The greater the contrast between the beam and the darkness outside of it, the harder it is to see objects outside the beam. A larger transition zone between darkness and light will help your eyes perform best in both conditions.

Thus, by considering how the human eye functions, you can put your LED flashlight or headlamp to more effective use.

[ photo by: Jule_Berlin, on Flickr, via CC License ]

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