The phosphor coating is usually distributed unevenly near the ends of
the tube where the metal caps are allowing the UV out and direct
viewing of the electrodes. Tubes specifically designed for UV output
like germicidal and EPROM eraser lamps use a glass which is more
transparent to UV. Quartz is needed for the 254nm mercury line and
synthetic quartz is needed for the 184nm mercury line.
There are a number of different phosphors which emit yellow near the
589nm sodium line which is safe for industrial photoresists. The
lower frequency safelight cutoff frequencies are 625nm (deep
ortho-red), 610nm (ortho-red), 580nm (amber), and 555nm
(amber-yellow). I think we used amber for black and white enlarging
paper in a darkroom.
On Mon, 22 Jul 2013 20:06:46 -0400, Jim Hancock <
jhancock1@...>
wrote:
>Probably not yellow glass but yellow phosphor coating. All fluorescent
>lamps work by using UV from a mercury vapor light source to excite a
>phosphor coating on the inside of the tube. Any missing phosphor will
>allow some UV to escape although most glass does block some UV rays.
>For what it's worth, Amazon has some 60 w bug lamps.