I know a lot of people get confused when people talk about frequency and nanometers and such, so it is helpful if you remember (or learn) that for all intents and purposes, ultraviolet is a color. Humans can't see UV, but most insects and a few animals can see some shades of UV. It is why a flower may look plain white to us, but be brilliantly lit to an insect. Here is a diagram that puts it in perspective:
The above in just a small slice of the electromagnetic spectrum. If you kept going to the left, eventually you would get to X-rays and gamma radiation. if you kept going to the right, you would hit microwaves, then TV broadcast frequencies. As you can see, ultraviolet it is just beyond violet ("ultra" literally meaning "beyond"), just as infrared is just below the color red (again, infra literally means "below"). UV is a range of colors, just like red is a range of colors. When we talk about 365nm or 287nm, we are simply talking about particular shades
of ultraviolet. Just as when we talk about 400nm we are talking about the highest violet that most people can see, and at 700nm, we are talking about deepest red that most people see. (Factoid: many people can see down to 1000nm and/or as high as 360nm, we are all as unique as snowflakes)
Just as different colors of light look differently, they do different things to UV curing finishes and plants. For example, in the case of UV, 365nm is not equal to 287nm just as blue is not the same thing as green. When a UV curing resin requires a particular frequency, it means it needs a particular "color", and a different color won't do very well. The same with plant stressing. Certain frequencies are what the plant expect, other "colors" may be too strong or simply not cause the reaction you are looking for.
Another thing to keep in mind is "energy". As you slide to the left on the scale, the energy levels go up exponentially
. The amount of damage you get from 300nm is over 10x as much as you would get from 320nm, with the same exposure time. This is why you need proper eye protection, and you have to take extra precautions when you are working with lamps that have UVB in their mix, as it is much more damaging to the skin and eyes than UVA.
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