I just checked and ruby is one of the few minerals that you might get a reasonable response from with that torch (ie some rubies, not all). I see some torches are 9W - that would be much better, and one with a range of say 400-300 nm would make about 70% of fluorescent minerals fluoresce, but with a range 400-280 nm almost any florescent mineral will fluoresce.
B5MECH - there are two different issues (I work with UV light):
(1) wattage - is it powerful enough? So yes, if you can use it inside in a perfectly dark room, close to the specimen, 4W will probably be adequate for some minerals that can flouresce in the short wavelength range that torch has.
(2) wavelength - will it fluoresce at all? This is important, for example, a ruby may fluoresce around 400 nm (few minerals will though) but a mineral like scheelite will not give any fluorescence whatsoever, no matter how high the wattage of your lamp. It has nothing to do with a weak or strong response, but with whether you get any response at all - not how well will it fluoresce, but CAN it flouresce AT ALL at that wavelength. Any particular mineral has to have light of a certain wavelength shining on it before it can fluoresce at all (fortunately it can be a bit of a range of wavelength), and the wavelength is different for different minerals. The problem is that people buy a torch and shine it on a particular mineral and it fluoresces and say "great, it works well" - but they don't realise that it is of limited range of wavelength that doesn't work for other minerals. Anyway, good luck.
In the list below, lw usually means in the range 400-315 nm, sw in the range 315-280 nm (and should only be used with protective goggles), The torch you got just barely scrapes into the edge of the lw range and not at all in the sw range.
Ultraviolet Fluorescence Chart
Abbreviations used in this chart:
lw long wavelength fluorescence
sw short wavelength fluorescence
The underlined section for some species and varieties (where applicable) indicates the general fluorescence encountered most often. Additional colors are also included. This does not mean, however, that all stones of a particular species or variety will show the fluorescence indicated for that stone.
FACTORS THAT MAY CAUSE DIFFERENCES, IN FLUORESCENCE:
Chemical impurities
Matrix and / or other foreign materials combined in or on this material.
Strain in the structure of the material
Isomorphous replacement
Please-note that it may be necessary to raise the stone up to the ultraviolet unit itself to obtain the required intensity of ultraviolet radiation necessary to produce the fluorescence indicated for a particular stone.
Amber None to yellowish green to orangey-yellow (lw) (lw works best). Also may fluoresce white, yellow, green or blue (lw), Fluorescence generally weaker under sw.
Beryl Emerald: (lw works best) none but may fluoresce weak orangey-red to weak red in very fine colors (lw and sw).
Oiled emerald: Oil shows yellowish to orangey-yellow(lw); weaker to non(sw). Oil will be noted in fractures.
Aquamarine: None
Blue Beryl: Green (sw).
Colorless: None to pale yellow or pink (lw and sw).
Golden: None.
Morganite: None to weak light red to violetish red (lw and sw).
Red: None
Synthetic Emerald Most synthetic emerald fluoresces a dull brick red (lw and sw) (lw works best). Some Gilsons fluoresce a weak to moderate orangey-red (lw and sw) to a moderate yellowish green (lw and sw). Gilson Group-III is inert.
Chalcedony All varieties: Generally inert (lw and sw); however, some may fluoresce a weak to intense yellowish green (lw and sw).
Chrysoberyl Alexandrite: None to weak red (lw and sw).
Yellow and greenish yellow: None to yellowish green (sw).
Other colors: Generally inert.
Coral White: None to weak to strong bluish white (lw and sw).
Light and dark shades of orange, red and pink: None to orange to pinkish orange (lw and sw).
Ox blood: None to dull deep red (lw and sw).
Corundum Burma ruby: Strong red (lw); moderate red (sw)
Ceylon ruby: Strong orange-red (lw); moderate orange- red (sw).
Siam ruby: Weak-red (lw); weak red to none (sw).
Pink sapphire: Strong orange-red (lw); weak orangey-red (sw).
Orange sapphire: None to strong orange-red (lw). Ceylong yellow sapphire: Moderate orange-red to
orange-yellow (lw); weak red to yellow-orange(sw). Green sapphire: None.
Ceylon blue sapphire: Moderate to strong orange to red (lw); weaker (sw).
Violet and alexandrite-like sapphire: None to moderate to strong red (lw); weaker (sw).
White sapphire: None to weak to strong orange to orange-red (lw and sw).
Brown sapphire : None to weak red (lw and sw). Black sapphire: None.
Colorless sapphire: Orange-red to red to orange (lw and sw).
Blue (dark) sapphire: None to moderate red (lw and sw).
Synthetic Corundum Synthetic ruby (flame fusion): Very strong orangey-red(lw); moderate to Strong orangey-red (sw).
Synthetic ruby (flux fusion): Strong orangey-red (strong, but not quite as strong as flame fusion or highly fluorescent natural material) (lw); orangey-red fluorescence generally stronger than natural, but some material may show zoned area of blue and /or bluish over tint on orangey-red fluorescence (sw).
Synthetic orange sapphire: Very weak orange to red (sw).
Synthetic yellow sapphire: Very weak red (sw).
Synthetic green sapphire: Weak orange (lw); dull brownish red (sw).
Synthetic blue sapphire: Weak to moderate chalky blue to yellowish green (sw).
Synthetic violet sapphire: Strong red (lw); greenish blue (sw).
Synthetic alexandrite-like sapphire: Moderate orange to red (lw and sw); may fluoresce red (lw), mottled blue (sw).
Synthetic colorless sapphire: None to weak bluish white (sw).
Synthetic brown sapphire: None to weak red (lw and sw).
Synthetic pink sapphire: Moderate to strong red (lw); pinkish violet (sw).
Diamond May fluoresce all colors with the exception of violet. General fluorescence is weak to strong blue (lw and sw).
Feldspar Albite: None to very weak brownish red (lw and sw).
Amazonite: None to weak yellowish green (lw). Oligoclase (sunstone): None to weak mottled white (lw and sw).
Transparent yellow orthoclase: None to weak reddish orange (lw and sw).
Orthoclase (moonstone): None to blue (lw); orange (sw). May fluoresce weak pink (lw and sw).
Transparent labradorite: None to weak blue (lw).
Garnet All species and varieties are inert with the exception of:
Transparent green grossluarite: None to moderate red (lw and sw).
Transparent colorless groosularite: None to weak orange or green (sw).
Ivory Weak to strong bluish white (lw and sw).
Jadeite Light green: None to weak white (lw).
Light yellow: None to weak green (lw).
White : None to weak yellow (lw).
Light violet: None to weak white (lw).
Some color-treated lavender: Weak to moderate orange (lw); weaker (sw).
Dark colors: Virtually inert.
Jet Inert.
Lapis Lazuli Generally inert; may fluoresce weak to moderate green or yellowish green (sw). The calcite inclusion may fluoresce pink (lw)
Malachite Inert
Nephite Inert
Opal Body color black or white: None to white to moderate pale blue, green or yellow (lw and sw); may phosphoresce.
Common opal or hyalite: None to strong green or yellowish green (lw and sw); may phosphoresce.
Fire opal: None to moderate greenish brown (lw and sw) ; may phosphoresce.
Pearl Natural: None to strong blue, yellow, green or pink (lw and sw).
Cultured: None to strong blue, yellow, green or pink (lw and sw).
Black pearl: Natural - none to strong red (lw); some may fluoresce light pink, mottled pink and white.
Dyed black: inert to weak white (sw).
Peridot Inert.
Quartz Green aventurine: None to weak grayish green (lw and sw).
Red dyed quartzite: Weak to strong red (lw and sw).
Rose quartz: None to weak red (lw and sw).
All other varieties: Virtually inert
Shell White: None to moderate blue to greenish white (lw and sw).
Tortoise shell: All but dark areas dull bluish green (lw and sw).
Spinel Red, orange and pink: None to weak red to orange-red (sw); weak to strong red and orange (lw).
Near colorless (rare): None to moderate orange to orange-red (lw).
All other colors: Virtually inert.
Synthetic Spinel Colorless: Moderate to strong chalky blue (sw); may fluoresce weak green (lw) and strong greenish blue (sw).
Light blue: Weak to moderate orange (lw); chalky blue (sw).
Medium blue: Strong red (lw); strong bluish white (sw).
Dark blue: Strong red (lw); strong mottled blue (sw).
Light green: Strong yellow (lw).
Dark green: Strong violetish red (lw); strong greenish white (sw).
Alexandrite like: Moderate dull red (lw and sw).
Yellowish green: Strong yellowish green (lw and sw).
Red: Strong red (lw).
Pink: Inert.
Topaz Colorless: None to weak yellow (lw).
Red: Weak brownish Yellow (lw).
Yellow: Weak orange yellow (lw).
Blue: None to moderate yellow (lw).
Brown: Weak orange-yellow (lw).
Pink: Moderate greenish white (sw).
Tourmaline Pink: None to very weak red (lw and sw).
All other colors: Virtually inert.
To quote one site that sums it up well:
"First things first. A "black light" will not work for most fluorescent minerals. Blacklights are long-wave UV. They are usually un-filtered. They are also cheap. Blacklights will make your laundry fluoresce, but they're not much good for most minerals. Do yourself a favor and take the $20 you were going to spend on a "blacklight" and put it toward a good mineral light. (A 4-watt, by the way, is not a good mineral light."
I just checked and the crash in the Australian dollar over the last few years has much more than doubled the price of lamps, so that something that is both sw and lw and with a filter (but only 4W and therefore needs complete darkness) is $180-200. So my advice is pretty useless for most people I guess (but then blacklight torches are mostly just as useless
e.g.
https://www.scientrific.com.au/product.php?p=1819
http://www.prospectors.com.au/p-10799-uvp-mini-4-watt-uv-lamp.aspx