Producing UV light

Common Sources of UV

• The Sun
  As the ozone layer becomes depleted increasing levels of UV reach the ground. However even still it is of too low an intensity (thankfully) to be of much use. The shortest wavelength (highest energy) at the Earth's surface is about 2920 Å and so you will not be able to erase EPROMs in sunlight.
• Solaria - UV tanning devices
  These generally emit in the UVA region and are therefore suitable for exposing photo-resist.
• Arc Welding Equipment
  The arc emits very strong levels of UV light due to excitation of atoms and molecules in the air. It is extremely impractical as a workable UV source.

Low-pressure Mercury Vapour Lamps

• White light fluorescent lamps
  Normal white light fluorescent lamps contain mercury vapour at low pressure. When excited the vapour emits UV light predominantly at 2537 Å. However a fluorescent phosphor coating on the inside of the tube absorbs radiation at that wavelength and radiates the energy back in the visible spectrum. The glass tube itself also absorbs UV so very little escapes.
• Germicidal lamps
  The same tubes can be made without the fluorescent coating and with thinner glass to obtain a source of 2537 Ålight. These are known as "Germicidal Lamps" and thus their output falls into the UVC region (See 7.2).
• Black-light lamps
  The same tube can be coated with a different phosphor which absorbs 2537 Ålight but emits it at 3650 Å. These are known as "Black-light Fluorescent Lamps" and thus their output mainly falls in the UVA region (See 7.1). About 2% of the total input power of these lamps can be emitted in the visible 3800 - 7600 Åband.

Ballast

Some UV tubes will the same ballast and starter as the equivalent visible fluorescent lamps as they only differ in terms of a phosphor coating. In fact it is often simpler to use a off-the-shelf fluorescent light fitting or lamp with a replacement UV bulb subject to the necessary safety requirements.

Note that some UV bulbs come with a self-contained ballast and/or starter. As usual, read the specifications !