If you are just getting into fluorescent minerals, selecting a lamp can be challenging (and possibly expensive).  This guide will explain briefly the differences between the lamps available to mineral collectors.

What’s the difference between a fluorescent light and an ultraviolet light?

This is confusing, because a lot of folks use the terms interchangeably. Typically a fluorescent light produces white light, and they are very commonly used in offices, schools and many homes as the primary artificial light source. Ultraviolet lights produce ultraviolet rays, and are used in germicidal applications, tanning salons, and to cause other objects (like posters) to glow (fluoresce). The confusion comes from the fact that fluorescent lights use ultraviolet rays internally to cause their phosphor coatings to produce white light externally, while ultraviolet lights produce ultraviolet rays externally to produce effects which white light doesn’t (like suntanning, or killing germs, or causing fluorescent objects to fluoresce).

What is ultraviolet light (UV)?

Scientists use a model of light that characterizes it by its wavelength; for example, the wavelength of red light is about 650 nanometers. Violet light has a shorter wavelength, about 400 nanometers. However, visible light is only a small part of the electromagnetic spectrum. Wavelengths just longer than red are called infrared (and invisible to humans), while light below the wavelength of violet light is called ultraviolet (also invisible to humans). Longwave UV peaks at about 360 nanometers, while shortwave UV peaks at about 254 nanometers. Midwave UV is generally considered to peak at about 312 nanometers.

What is the difference between longwave and shortwave UV lamps?

True longwave UV lamps produce mostly longwave UV light; they have a filter which screens out most (but not all) visible light. "Blacklights" are an inexpensive way of producing longwave UV; they too have a visible light filter, but it is much less effective than that on a true longwave UV lamp. For most beginning hobby and display applications, "blacklights" work just fine. Longwave UV light is present in sunlight, and is not harmful to humans.

Shortwave UV lamps come in two types – filtered and unfiltered. Unfiltered shortwave lamps invariably produce a lot of visible light in addition to the shortwave UV light; they are fine for germicidal applications, or tanning applications, but are largely useless in examining or displaying fluorescent objects – the visible light produced simply drowns out any fluorescence produced. Filtered shortwave lamps use a very expensive filter which allows shortwave UV through, but filters out almost all visible light; they are the ones which are used by scientists or hobbyists observing fluorescent minerals. Midwave UV lamps use the same filter used by shortwave lamps, but use a special phosphor inside the tube to produce mostly midwave UV light. Although both midwave and shortwave UV are produced by the sun, our Earth’s atmosphere filters out virtually all of the shortwave UV, and most of the midwave UV as well. This is a good thing, because long-term exposure to midwave and/or shortwave UV light is suspected to cause skin cancer and cataracts.  For protection, you should always wear safety glasses (which block UV) when using shortwave or midwave UV lamps. Limiting skin exposure is also a good idea.

What kind of lamp do I need for fluorescent mineral collecting?

The good news: for beginning hobbyists, an inexpensive "blacklight" is a good way to get started; they are widely available, fun, and will work fine for minerals which fluoresce brightly when exposed to longwave UV (Wernerite and many specimens of Fluorite, Calcite, and Sodalite are good examples).  Small battery-powered "blacklights" are available for field collecting, at least for beginners.

The bad news: Most minerals don’t fluoresce at all, and of those that do, only a few are really bright under longwave UV. In order to see all the bright colors which make fluorescent minerals so attractive, eventually you will want to buy a good shortwave UV lamp. These are generally much more expensive than longwave UV lamps, and also should be used with care – protective eyewear should always be worn.  A good battery-powered shortwave UV field lamp will cost at least $150-$200+, and a higher-powered display lamp will run $300-$400+.  Midwave lamps are usually purchased only by advanced hobbyists, and are at least as expensive as shortwave UV lamps.  

Are ultraviolet lamps safe? 

So-called inexpensive "blacklights" produce only longwave ultraviolet (UVA) rays, along with a good deal of visible blue. A scientist’s (or serious hobbyist’s) longwave lamp will have considerably more power, and produce significantly less blue light; it will also cost significantly more. Longwave UV lamps are not harmful to eyes or skin, but their use by very young children should still be supervised. These lamps are quite safe.  Even junior rockhounds can use longwave or 'BLB" lamps without worry, because it will not cause any problem for skin or eyes, even if used a fair amount.  The powerful "blacklights" sometimes used at rock music shows, and sold for use in lighting up posters, etc., are longwave-producing lamps, and are safe to use as well; they cost significantly less than a serious researcher’s longwave lamp.

Shortwave lamps are a different matter entirely!  Shortwave UV lamps produce shortwave (UVC) rays, which are the type that can quickly produce a "sunburn", or "welder’s flash", basically a "sunburn" of the eye. High exposure over a longer period can promote skin cancer, and has been thought by some to produce cataracts. These lamps should always be used with eye protection. Unfortunately, I have seen eBay auctions advertising low-powered, relatively inexpensive shortwave lamps as safe, as long as you "simply don’t look into the light"; please don’t you believe it! First, many children, when told not to do something, will simply wait until you’re looking the other way, and then do it!  Second, anything you shine the lamp on will reflect some of the shortwave rays – right into your eyes.  And finally, lower-powered lamps require total darkness to be effective; however, the lower the level of ambient light, the more your pupils will dilate – thus letting even more shortwave UV into your eyes.  Fortunately, safety glasses (and even most ordinary window glass) will do a good job of protecting young eyes.

The good news is that used with care, and with adequate eye protection, shortwave lamps are wonderful tools that produce brilliant fluorescence in many more minerals than longwave lamps can. Because of this, most rockhounds who really get into this hobby eventually "graduate" from longwave lamps to shortwave; this is fine, as long as they treat these tools with the respect they deserve (and use the proper safety precautions).  Their major drawback is cost:  a good battery-operated field lamp can cost well over $200, and a display lamp over $400.  Make sure that you are ready for this type of lamp before making the investment; then make sure that it is always used with the proper safety precautions and adequate eye protection.