What is P22?
Bryan Kennedy
Hi all,
I am trying to locate a specification for the "P22" phosphor set
commonly used in computer monitors. Does one exist? I am particularly
interested in the RGB spectral power distributions (SPDs). The term
"P22" is confusing; does it describe a set of phosphors? Any help would
be appreciated.
Bryan Kennedy
Karl Storz Imaging
Tom Lianza
Brian,
P22 is a JEDEC designation for a three color phosphor screen for use in color
television which covers six different phosphor systems, with different
chemical compositions, different CIE coordinates and different emission
spectra. The following chemical families are specified:
sulphide/silicate/phosphate
all-sulphide
sulphide/vanadate
sulphide/oxysulphide
sulphide/oxide
sulphide/oxysulphide-modified
Each family has three phosphors a Red, Green and Blue.
None of the chromaticities for any given color are identical between any
family.
Most computer monitors do not really use a physical P-22 set. They specify a
set of phosphors with P-22 characteristics.
Modern classes of monitors are being designed with phosphor sets that have
been designed to meet stringent disposal requirements found in the European
Market, so don't assume anything about any monitor's chemical family.
I'm sorry that this wasn't an easy answer..... If you would like spectral
plots of a typical phosphor set, email me and I'll send you some 10nm spectral
data from a Sony, Nec, or Mitsubishi monitor. I'm sure that I have the data
on this machine somewhere.
Good Luck,
Tom Lianza
Technical Director
Sequel Imaging
tli...@sequelimaging.com
Matthew Brennesholtz
I agree with Tom Lianza, and would like to add my 2 bits.
P22 is in fact an obsolete designation, even though it is sometimes
still encountered. Other obsolete designations for the same phosphors
are "X" and "XX". The correct current designations are XXA through XXF.
These are EIA registered phosphors. See http://www.eia.org/ XX series
phosphors are intended for color entertainment, other X series phosphors
(XBA, etc.) are intended for computer monitors where the color points
are essentially the same as TV color points. Phosphor spectra for a
particular registered phosphor are in EIA Publication TEP 116-C, about
$100 (1993 price when I got my most recent copy) from the EIA.
The EIA "D" series of phosphors (i.e. DAA, DBA, etc) are also tri-color
phosphors intended for data display applications. In the D series, at
least one of the phosphors is significantly different in color from the
P-22 phosphor. Most commonly blue is desaturated to a blue-white. In
other cases, the green is more saturated.
There is no practical way to tell what phosphor is used in a particular
TV or computer monitor. Two nominally identical TVs or monitors with
same brand, the same model number and the same date of manufacture may
in fact contain different phosphors. In other words, if you want to
know the spectra of the red, green and blue phosphors in a particular
monitor, there is nothing you can do except measure them.
Broadcast TV in the US is encoded for the SMPTE C phosphor set. HDTV
will also use the same colors. The SMPTE spec defines the color points
of the phosphors, not the spectra. SMPTE C is defined in "SMPTE C Color
Monitor Colorimetry" RP 145-1994. "Monitor" here refers to TV studio
monitor, not computer monitor. See http://www.smpte.org/ This
definition replaces the old NTSC definition of TV color points. Of
course, Europeans use a different set of color points called the EBU
phosphors. These are close enough to the SPMTE C colors that the
difference rarely causes problems. SMPTE C colors are defined as:
CIE x CIE y
Red 0.630 0.340
Green 0.310 0.595
Blue 0.155 0.070
Very broadly speaking, any phosphor set where the colors match the SMPTE
colors and the phosphors are intended for consumer TV can be spoken of
as a modern P-22 phosphor. Older P-22 phosphors had different color
points. In particular, the green was originally significantly more
saturated.
Matthew S Brennesholtz
Philips Research
Briarcliff Manor, NY 10510