This is a good question because it's often asked. But there are differences which apply to LEDs and UV lights in particular. And this is important to note for UV users.
In summary, watts is not a meaningful measure for the intensity of LEDs (you can read below as to why). Lumens and LUX are not measures we use in the UV LED industry because these only apply to visible light LEDs. Instead in the UV industry we use radiant intensity and irradiance to measure how intense and how powerful a UV light source is. The below is a more detailed explanation for those interested. Otherwise jump to the end of this FAQ to read off the specifications.
"Watts" as a measure of brightness for LEDs is not a meaningful measure of brightness in the LED industry because wattage is talking about the energy it takes to produce a certain amount of light. This worked well with filament and incandescent lamps where the higher the wattage the brighter the light. The trouble is that the lighting industry has advanced such that wattage values are not directly translated into brightness - it's possible to have a lower wattage LED and yet it is a brighter light relative to another light source or LED with a higher wattage. Moreover, depending on the electronics and the efficiency of the LEDs, the energy (watts) supplied is NOT directly translated into light at 100% efficiency. Much if not most of that energy (wattage) is lost through heat whereby very little is actually translated into light. You could have a very high wattage LED, but most of that energy will not be directly translated into the useable light that you're after. So the LED industry has moved away from using wattage as a standard for brightness. So wattage doesn't really speak to how bright an LED light is.
So the LED industry mainly use terms such as Lumens, LUX, and Candela. Lumens is the measure of how intense the resultant or actual emitted light is and is measured in lumens. The higher the lumens the more intense the light emitted. LUX or luminous flux is the measure of light falling within a given unit of area. This is a measure of the density of the light emitted and how it's dispersed or spread. For instance you can have a very high Lumens rating but a low LUX rating depending on how the beam is emitted. It's the difference between a 500 watt light bulb and a small 50 lumen flashlight. Which one is brighter? The 500w light bulb because it can light an entire room. Which one is more powerful over a given area? The 50lm flashlight because it channels it's light into a particular viewing area. See the relevance of terminology here to give a more meaningful understanding? (We won't go into candela, steradians, and the solid angle measure, nor the inverse square law of light, as it's a bit of an overkill for this).
Now here comes the twist with ultraviolet light (or radiation to be more exact). Note: Don't freak out with that word radiation, because it is just describing the energy along the electromagnetic spectrum where visible light is also a type of radiation along with radio waves.
Lumens and LUX measurements only pertain to visible light. So this suits the regular flashlight industry and their users can happily converse with one another all day long. But UV is light which does not fall into the visible spectrum. So the UV industry to describe the attributes of their light sources cannot use terms such as lumens or LUX. This is only used as a measure of the light observed.
In the UV industry we use radiant intensity and irradiance to measure the same thing (Lumens and LUX respectively).
Radiant intensity is the measure of ultraviolet radiation actually emitted or output. Which is what you want or should know. It's the useable UV light you're going to use - remember wattage in a UV light is NOT meaningful as it attempts to describe the watts going in to power an LED semi-conductor. But that energy is mostly lost to heat, internal resistance, etc. And this can vary widely with systems being 80% efficient to 20% efficient. The input watts will mask this rather badly.
What's important to look out for is the energy that comes out of the business end - the actual radiation emitted. That's what actually and really counts. So radiant intensity of a UV flashlight is the actual UV energy emitted and is measured in watts or more typically milli and micro watts. This tells you the true intensity of UV being emitted.
Irradiance is like LUX but for ultraviolet light. Irradiance is the amount of ultraviolet falling on a given unit area and is measured in watts per square meter, or more typically milli or micro watts per square centimeter.
So, in a nutshell lumens and watts are not used by the UV industry to measure performance of UV LEDs. Instead radiant intensity and irradiance are.
Technical information we know, but we thought it deserves an explanation.
Now you can make sense of the following.
Here are the specs for the V3 365nm:
UV wavelength: 365nm
UV Radiant Intensity: 1350mw
UV Irradiance: 5400uW/cm2 from approx. 24 inch distance