Leo van Loon wrote to me:

> I experienced that the relative big (15W) in free air also produces
> ozone in very irritating quantities. Packing the tube tight in
> aluminum foil leaving only a small window for the PIC's reduced that
> problem to zero.

  And I repied:

  Ozone production demonstrates that it is working!  It makes good sense
that if you limit the amount of air exposed to the radiation, you limit
the amount of ozone produced.  If you don't physically let the ozone
escape, it reaches an equilibrium where it degrades just as fast as it
is produced.  The ozone is also responsible for part of the damage the
UV does to the plastic case too!

  I had my hair cut the day before yesterday (you will be pleased to
know!).  The hairdresser opened the steriliser and got out a comb or
something; the UV light stayed on!  "Oh yes, the switch broke and it
would cost too much to have it fixed".  Ho Ho!

  Cheers,
        Paul B.