BLACK LIGHT: Be careful of your scource

UV light is light with wavelengths shorter than 400nm, in the range of 280nm up to 400nm. There are three wavelengths of ultra violet light, long wave and short wave; UVA, UVB and UVC; UVA stands for the range from 320 to 400 nm, (short wave,) UVB for 280–320 nm, (long wave,) and UVC for 200–280 nm, (vacuum uv -- because it is rapidly absorbed in the atmosphere and exists mainly on outer space.)

The range 250 to 315nm, UVB is particularly dangerous to the skin and eyes and should be avoided.

When buying UV lights for stage use you should be cautious to buy UVA or UVB suppressed light sources. Buying reputible theatre lighting devices from a well known stage supply business like BMI Supplies, www.bmisupply.com; Grand Stage Company, www.grandstage.com, or Mainstage Theatrical Supply, www.mainstage.com; is essential. Only known responsible suppliers should be chosen to provide luminaires for your performance -- unless blindness or sunburn is a desireable stage effect.

If you use flourescent tubes as a light source, use only BLB type lamps, not BL. BLB lamps have built-in filtering to only allow UVA wavelengths to be emitted.

MaiKätzchen

Andrew,
Thanks for sharing this information with the Loft.

As you say, UVA lamps which peak at 365nm are the best bulbs for what we do and are safe. These are generally identified as a BLB which means "Black Light Blue" - they have the dark purple coating which filters out any harmful rays. But only the fluorescent tube bulbs will work. Those black light bulbs with a screw in base (known as an Edison base) will NOT work with the chalks we use.

As has been noted on this site before, the black light LED fixtures do not work well with our invisible fluorescent pigments. That means the chalks we use to do hidden drawings will not respond well to the LED fixtures. You will lose almost all of the color and much of the luminosity - some of the colors will not glow at all. This may change as technology or pigments change but, as of today, that is the way it works.

Best,
Kerry

I didn't mention LED fixtures for that reason. Good narrow spectrum black light LED lamps are available, but are so expensive that a fixture with 36 3W lamps, about the minimum flood design for a 8X12' area, would cost about USD 2,500.

Your Servant,

MaiKätzchen

Thanks for the follow up!

Most of my comments were meant for those who are not professionally acquainted with stage lighting. With the information you provided, I'm guessing you are .

Holy cow! $2500! Do you know of any LED fixtures that peak at 365nm (or the equivalent of a BLB tube) that would wash a 4' x 5' area? Please send me a link if you do. I bought a couple "black light" LED flashlights (which were not cheap), and was completely disappointed with how invisible chalks responded. The regular fluorescent chalk responded pretty well but not the invisible colors (also called "black light chalk" by Eternity Arts).

Do you do chalk art yourself? If you are in Springfield, MO too we should connect.

Best,
Kerry

Yes, and we talked often at the Sal. How is the job search going?

MaiKätzchen

Oh. Your screen name threw me off. This must be the business partner of the late Mr. Marley?

I'm still looking for someone who thinks my skills are worth hiring. We have about two weeks left to solve that or we will be homeless. No one wants to rent to the unemployed. Can't blame them.

Yet, as Thanksgiving approaches, we still have much to be thankful for.

Thanks,
Kerry

Yes, and that unspeakable day is still HUMBUG!

E. Scrooge