Everything You Need to Know About UV LED flashlights

UV LED flashlights are great tools for seeing and observing things that are normally invisible. But with so many choices and technical terms, it can be a bit confusing and challenging to know if you are making the right purchase. Read our guide to be assured that you're getting the best product!

What exactly is a UV LED flashlight?

A UV flashlight emits ultraviolet radiation - a type of light energy - that is not visible to the human eye. When ultraviolet light hits certain objects, they can fluoresce - a phenomenon similar to a bright glow. Many objects and substances such as paints, dyes, minerals, animals and body fluids exhibit fluorescence, which means that the presence of these things can be detected only when a UV light source shines on them.

A UV flashlight takes the same shape and format as a standard white light flashlight, but instead of emitting white light, emits ultraviolet light. Virtually all UV LED flashlights use LED technology.

Should I get a UV flashlight for my application?

UV lighting has a wide variety of applications, but UV LED flashlights can be most useful in situations where portability and ease of use is important. UV LED flashlights are generally not strong enough to induce any chemical or physical reactions (e.g. curing) but provide enough UV light to observe fluorescence effects.

Below are some use example cases of UV LED flashlights:

Forensics & counterfeit verification

Mineral & gemstone observation

Checking for urine stains (e.g. pets) or other body fluids

Searching for insects and reptiles

Does it matter which UV flashlight I use?

Because UV LED flashlights vary in their type and quality, it can be difficult to know if, and which UV LED flashlights will work for your particular use case without looking at the specifications. See below for things to look out for:

Get the correct wavelength. UV light is actually a general term for a wide range of UV wavelengths across the UV spectrum. Just like visible light is measured along a visible spectrum, UV light is also described along a spectrum using its wavelength, measured in nanometers (nm). When looking for any UV light, it is extremely important to know what wavelength (in nanometers, or nm) the light is emitting at.

Why is the wavelength so important? 

Well, in short, to be useful, a UV light needs to induce fluorescence. Not all UV wavelengths are capable of producing sufficient fluorescence effects, so you could be completely missing the mark, by purchasing the wrong wavelength.

Although optimal wavelengths can vary across materials and objects, most fluorescence is strongest in the wavelengths around 360 nm. Therefore, it is important that you purchase a UV flashlight with a wavelength at or near 365 nm - otherwise, the UV energy produced by the flashlight may be completely useless and producing the fluorescent glow you are looking for.

Because of the trends in LED manufacturing, higher wavelength LEDs are easier and more cost effective to manufacture. As a result, 415 nm (visible, violet light) LEDs and 405 nm (borderline visible violet light) are often used as "ultraviolet" LEDs. If a seller or manufacturer does not list the wavelength used - be careful - as they could very well be using a violet or purple LED that is not a true UV light source.

A common wavelength option is 395 nm. Strictly speaking, these are considered to be ultraviolet LEDs when we use the definition of < 400 nm to define UV. But because these LEDs are so close to the 400 nm cut-off, they still emit much of their energy as violet light. As a result, many objects will be illuminated in a dull violet color, without providing enough lower-wavelength UV light to induce fluorescence.

Does it provide enough power? Even the correct wavelength of UV light can be useless if there simply isn't enough of it. In other words, you need to make sure you have both quality (good wavelength) and quantity.

But how do you know how much UV light is being emitted? Unfortunately, this is a tricky specification that most products do not list. Unlike white flashlights that use the lumens metric to describe brightness, because UV is invisible, this measure does not apply.  Although there are ways to measure UV light, this may not be too practical when shopping for UV LED flashlights, as most manufacturers will not provide much information.

Generally, two aspects of a UV flashlight's design will dictate how much UV light it can pump out. The first is the power consumption, usually rated in watts. Most smaller flashlights will run at 1W or so, while larger flashlights may run at 3W or more. Don't be fooled by the LED quantity - just because there are more LEDs does not necessarily mean that there is more power. What matters is the total power - 1 LED running at 3 watts is more power than 3 LEDs running at 0.5 watts each.

The second aspect is LED efficiency. Not all LEDs convert the same ratio of electrical energy to UV light energy, and this can play an important role in determining the amount of UV light energy is ultimately emitted. A low efficiency LED can mean that even a high power UV flashlight is not actually producing much useful UV light output. It isn't easy to determine UV LED efficiency, but generally, look out for lower-priced UV LED flashlights, as the LED chip is typically the most expensive component in a flashlight, and low efficiency values are typically the result of low-cost or over-driven LED chips.

How is it powered? 

Many UV LED flashlights can be powered via disposable AA or AAA batteries. This is often the lowest-cost and practical approach for occasional, light use - if, for example, you only use it for several minutes at a time to check for pet urine. What if you expect more rigorous or extended use? You may want to consider a rechargeable option.

The most common battery type is called the 18650, a rechargeable lithium ion battery. 18650 batteries can hold up to 2500 mAh (at 3.6V) or more, which is equivalent to approximately 3-4 of the disposable AA battery type. By utilizing a rechargeable battery pack, you will save on long-term battery costs. Many UV LED flashlights will also include a USB or similar charge port for rechargeable batteries.

18650 batteries come in two variants - protected and unprotected. A protected 18650 cell includes an integrated circuit that protects the battery from overheating, exploding or leaking. Although protected batteries do cost a bit more, the risk of an exploding battery caused by a lack of circuit protection could mean the difference between a house burning down, or a bodily injury occurring or not.

Is UV light from a UV flashlight harmful or dangerous?

Disclaimer: The content published below is for informational purposes only. It is not intended to be a substitute for professional medical advice and should not be relied on as health or personal advice.

Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition. Never disregard the advice of a medical professional, or delay in seeking it because of something you have read on this website.

UV light is often portrayed in the news and media as harmful, so you may be concerned about whether or not UV LED flashlights are safe. The short answer is, they are generally safe as long as you follow some common sense rules, which we discuss below.

But first, it is important to understand the risks behind UV light and where UV LED flashlights sit in terms of those risks. Just as we discussed that wavelength and power are the determinants of how strong fluorescence effects are, the risks and danger of UV light are also dependent on wavelength and power.

We receive significant amounts of UV-A (315-400 nm) and UV-B (280-315 nm) from the sun. UV-B wavelengths are shorter, and are therefore more harmful.  Most of the risks associated with excessive exposure to sunlight (sunburn, eye irritation and cancers) are a result of UV-B wavelengths. Because UV LED flashlights emitting at wavelengths 365 nm or higher are emitting in the UV-A range, they can be thought of as being less harmful than the UV-B wavelengths.

Generally speaking, the overall amount of UV light emitted from a UV flashlight is also much less than what you would find outdoors on a sunny day. Natural sunshine has about 32 watts of UV energy per square meter, which is more than 30 times the amount of UV energy emitted by a 3W UV flashlight (assuming a 30% efficiency value).

While we see that a UV flashlight's potential for harm is much smaller than natural sunlight, we also cannot completely dismiss the potential for danger and harm in a UV flashlight, either. To further reduce these risks, there are certain steps that can be taken.

First and foremost - never look directly into the UV flashlight. UV light is invisible, and does not induce the same natural reaction to squint or look away, the same way we would if we were to look directly into a white flashlight. Just because it doesn't appear bright, doesn't mean that it's not emitting lots of UV light. Be sure to keep the UV LED flashlight away from children or anyone who is not aware that the flashlight emits UV light.

If you are still a bit uncomfortable about the safety aspects, you can take further steps to further protect yourself, just as you would out in bright sunshine. For example, you may want to purchase UV-blocking safety goggles or sunglasses, which will help reduce the amount of UV light from hitting your eyes. When using the UV flashlight, you can also try to avoid shining the light directly onto bare skin, and wear long-sleeve clothes. And, as a practical matter, keep the UV flashlight turned on only as long as is necessary.