Table 1. Color and CIE color coordinate (as of April 2000) 
| Name of Color |
CIE color coordinate (TYP) | Brightness
Ratio 1) |
| New Name | Previous Name | X | Y | % |
| Blue (B) | Blue | 0.14 | 0.18 | 15 |
| Light Blue (lt.B) | Neo Blue | 0.18 | 0.19 | 10 |
| Light Greenish Blue-N (lt.G.B-N) | Sky Blue(Blue) | 0.18 | 0.27 | 20 |
| Bluish Green (B.G) | Sky Blue 2 | 0.20 | 0.40 | 45 |
| Green (G) | Blue Green | 0.24 | 0.41 | 100 |
| Vivid Green (vv.G) | Emerald Green | 0.10 | 0.73 | 20 |
| Yellowish Green (Ysh.G) | Neo Green | 0.28 | 0.62 | 20 |
| Yellow Green (Y.G) | Lemon | 0.38 | 0.57 | 40 |
| Greenish Yellow (Gsh.Y) | Yellow | 0.47 | 0.51 | 30 |
| Yellowish Orange (Ysh.O) | Amber | 0.53 | 0.47 | 30 |
| Orange (O) | Mandarin | 0.60 | 0.40 | 20 |
| Reddish Orange (Rsh.O) | Red | 0.64 | 0.36 | 10 |
Note 1) Brightness ratio when Green (Blue Green)=100%. These brightness ratio are just for reference.
The ratio in this table are measured under the same electrical test condition;
ec=eb=26Vp-p with 1/16 pulse duty. This value may vary.
It depends on the VFD's construction and the driving conditions.
Fig 1 CIE Chromatocity Diagram
Fig 2 Spectrum of color phosphor material
Note: Peak wave length of each color may vary and the figures in the above are for reference only.
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If as a definition, Green (Blue Green) is rated 100%, each of the colors when driven
under the same conditions would be rated as shown in the Table 1.
Although there are different brightness characteristics between phosphors,
this is not always readily apparent because a sensitivity
of human eyes to brightness varies with color wavelength.
Therefore, legibility may not be affected.
In a multicolor display specific brightness balance can be achieved
by controlling voltages and/or duty factor of each color.
Note: These figures are for reference only,
because the brightness depends on its driving conditions.
2. Optical Filter
The major function of an optical filter is as follows;
- To achieve greater contrast
- To adjust the luminance color
- To protect the Vacuum Fluorescent Display
2.1 Contrast
Phosphor, which has a whitish color may reflect ambient light.
This reflection reduces the contrast ratio between active and inactive segments.
In this case, a gray color optical filter which has a flat spectrum transmission
improves contrast.
In general, a 5 to 30% transmission filter (cut 70 to 95%) is recommended.
2.2 Color Adjustment
(1) Mono-color display
Color can be changed by utilizing optical filters.
Green (Blue Green), the basic color of VFD has a broad spectrum which can produce
many varieties of colors by using various color filters.
(2) Multicolor display
It is possible to show many different colors in a multicolor display
with just one optical filter.
For example, a pinkish color filter shown in Fig. 4
changes blue-green and red into white and vivid red.
Although this application note APN301 has described the use of color filters,
when it is necessary to have different color annunciator,
we recommend changing the actual display color and utilizing a neutral gray filter.
Fig 3 Examples of Transmission Curves of Color Filters |
Fig 4. Pinkish color filter Transmission Curves
(for multicolor display) |
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