What is the difference between 365nm and 395nm UV flashlights?
by storesuperfire on Sep 17, 2022
Differences between 365 nm and 395 nm UV lamps
Both 365 nm and 395 nm are in the UV-A wavelength range. In general, UV-A UV lamps can be used to generate and observe fluorescent effects, as well as to cure plastics and paints. UV-A wavelengths are safer compared to stronger UV-B and UV-C rays.
So what does the 30 nm difference mean?
The main difference is that 395 nm LEDs emit more visible light than 365 nm LED UV lamps. 395 nm LED UV lamps emit a distinct purple light, while 365 nm LEDs emit a dull blue-white light (a result of residual light energy "smearing" into the visible spectrum). Both types emit in the UV-A wavelength range and are often capable of producing a "black light" or curing effect.
Why is there a difference in the amount of visible light?
The graphs above show the spectral output plots for the 365 nm (narrow dashed line) and 395 nm (wide dashed line) LEDs. You'll notice that both 365 nm and 395 nm LEDs emit in wavelength ranges above and below their respective wavelengths. In other words, 395 nm LEDs do not emit light only at 395 nm.
A 395 nm LED emits most at 395 nm (defined by the term peak wavelength), but it also emits quite a bit of energy at 400 nm or even 410 nm. These wavelengths are fixed in the visible violet part of the spectrum.
Of course, 395 nm LEDs also emit wavelengths below 395 nm, and these wavelengths of light can be very effective at producing fluorescence effects or initiating UV-A reactions. However, as shown, it is important to note that most of the light energy is emitted in the visible purple region.
Conversely, looking at the 365 nm spectral output, you'll notice that nearly all of the light energy is only in the invisible UV-A range, with the emission energy tapering off before reaching 400 nm. This will maximize the amount of UV-A energy compared to visible light energy and is preferred for most UV-A applications.
However, when illuminating a 365 nm LED, you may notice a dim blue-white glow. This is caused by visible light "leakage" in which a small but visible amount of visible wavelength energy (i.e. white light) is also emitted. The proportion of this visible light energy is so small that it appears as a "0" in the spectrogram, but in some applications, such as UV photography, visible light is indeed detectable and can be annoying. In this case, additional visible light filtering techniques may be required.
365 nm UV lamps are more fluorescent than 395 nm UV lamps
In addition to 365 nm UV light, which has the advantage of not emitting violet light, many objects fluoresce most strongly at 365 nm, as evidenced by absorption spectroscopy measurements.
The result is that 365 nm light may be more suitable for applications requiring stronger fluorescence. Combined with the advantage of emitting less visible violet light, 365 nm light can be considered a better choice where performance is critical.