Electromagnetic waves: the good and the bad
As a fisherman, it’s common for you to think and talk about waves – the kind you encounter when working on the ocean.
But what about electromagnetic waves? The radio waves powering your VHF radio; the light waves enabling you to see other boats; or the waves warming and tanning your skin.
Fishermen are in a sea of electromagnetic waves all day long – most of them good waves, but some of them not so good.
Electromagnetic waves are organized into categories. Radio waves have the longest wavelengths and gamma waves have the shortest wavelengths. (See graphic on next page.)
The good waves
On your boat, the VHF radio, radar, and cell phone all work on radio waves. The GPS navigation and satellite communication rely on microwaves. These instruments are sensitive and need to be maintained and used carefully. They are critical for safe transit and fishing: they give you weather forecasts, boat to boat and ship to shore communication; they are vital for navigation and collision avoidance.
Infrared electromagnetic waves are responsible for the warmth we feel in the sun but are not a major player on the boat unless you have a TV remote or night vision equipment.
The domains of the electromagnetic spectrum.
Graphic courtesy https://www.bbc.co.uk/bitesize/guides/zdx4t39/revision/2
Fish finders, however, operate with ultrasound waves rather than electromagnetic waves. Ultrasound waves are generated by a transducer mounted on the bottom of the boat; the ultrasound waves reflected by the sea bottom and fish are captured by the transducer and transferred to the fish finder screen. The transducer must be properly mounted on the bottom of the boat for the unit to pick up the fish.
The difference between electromagnetic waves and ultrasound waves can be summed up easily: electromagnetic waves can pass through a variety of media or empty space, whereas ultrasound waves can only pass through a medium such as air, water, or a solid.
Finally, the other good waves we want to mention are those of the visible spectrum. This is the spectrum that gives us the rainbow of colors: red, orange, yellow, green, blue, indigo, and violet. As you can infer from the graphic, we can actually only see a very small band of the entire electromagnetic spectrum. The visible spectrum is that band we can see.
The bad waves
Beyond the violet band of the visible spectrum is ultraviolet light, which is made up of UVA and UVB spectra. UVA is the wavelength band that reaches earth, while the UVB band of electromagnetic waves is largely captured by the ozone layer in the stratosphere before it reaches the earth.
UVA light is the light we most need to worry about. While this band of short wavelength waves cannot penetrate deeply into our skin, they can penetrate enough to cause tanning and make changes in the DNA of our skin cells. While exposure results in tanning especially in light-skinned people, prolonged exposure to sunlight – UVA and UVB – can result in skin cancer (a carcinoma or melanoma). These ultraviolet bands can also result in cataracts in the eye and/or cancer in other eye tissues.
Therefore, we should be actively stopping the UVA and UVB waves from reaching and penetrating our skin by using sunscreen with a Sun Protection Factor (SPF) of at least 15 with SPF 30 preferred. The higher the SPF value, the more sun protection the product provides. These SPF numbers do not relate to how much more time one can spend in the sun with sunscreen on; they indicate how much protection the sunscreen product provides relative to the sun’s energy. In strong sunlight, a high SPF is needed; in lower sun energy (say, early in the morning), a sunscreen with a lower SPF is adequate. More than one application of sunscreen may be needed in a day depending on the amount a person is sweating or swimming.
With respect to protecting the eyes and slowing the development of cataracts, sunglasses labelled “protect from UVA and UVB” are the only ones that will be protective. Some sunglasses are just colored glass; these will not protect the eyes.
For those of you with children or grandchildren, try to get them in the habit of wearing sunglasses. Adding a hat helps protect other parts of the eyes (such as lids) from the sunlight that comes in at the sides and top of the glasses.
Ann Backus, MS, is the director of outreach for the Harvard T.H. Chan School of Public Health’s Department of Environmental Health in Boston, MA. She may be reached by phone at (617) 432-3327 or by e-mail at <abackus@hsph.harvard.edu>.
