This needs to be said. Over the years a few disreputable sellers have been marketing a little 4/6 watt shortwave light for fluorescent minerals. I see that at least seven have been sold on Ebay for $16 to $18 over the past 3 months.
These lamps are garbage!
Most recently they are listed under the title: "UV Light Shortwave Ultra-Violet Lamp Detector Fluorescent Multi-Color 6H9". They do not have a visible light blocking filter (commonly referred to as a Hoya UV filter). The lamp emits tons of visible light and requires a filter to be useful for viewing fluorescent minerals. A few minerals such as Franklin willemite/calcite will exhibit a very washed out fluorescence, but none will appear as seen in the pictures here on Nature's Rainbows. (For more on UV and filters explore here.) On top of that, they are very low power. 4 watts is a gift; my bet is that they put out 3 watts or less - and that is referring to the power, the visible light. UV output is in the range of 0.25 watts.
Most I've seen lately are pink and sold by various sellers from China. They run off of 4 "AA" batteries and are listed as not having an "optical filter" (a result of a deluge of complaints I'm sure). Some show pictures of fluorescent rocks illuminated by this light but make no mistake - those are the only rocks in the world which will exhibit even the washed out fluorescence seen under this light.
You will also find cheap longwave (blacklight) lights. These aren't much better. Although they use a filtered blacklight bulb, they are still very underpowered, small, and pretty useless for anything but a toy. Don't waste your money on these toys. The fluorescent mineral hobby may be a little expensive to get started with but the beauty and fun finding these minerals at night are well worth the initial cost to get started. These little blacklights sell for $6 and up.
At least one USA company makes a 6 watt "enhanced" light and sells it for around $90 with a visible light blocking filter. I have not tested or seen one of these units but I'm sure it is magnitudes better than the junk from China. But I still would recommend investing a few more $$$ in a real mineral light with some power and decent light output. You'll be much happier with your investment.
See our lights page for more information.
Disclaimer: Nature's Rainbows does not sell lights. We have no connection with any manufacturers of lights. We are technical and understand lighting and mineral lamps intimately. These lights shown here are junk.