Page 65 - Sensors and Control Systems in Manufacturing

The Role of Sensors in the 21st Century
Standard Brightness High Brightness 27
LED Chip lpk Iv Viewing Chip lpk Iv 3 Viewing
Color Material (nm) (mcd) Angle Material (nm) (mcd) Angle
Red GaAsP/ 635 120 35 AS 635 900 30
GaP AlInGaP
Orange GaAsP/ 605 90 30 AS 609 1,300 30
GaP AlInGaP
Amber GaAsP/ 583 100 35 AS 592 1,300 30
GaP AlInGaP
Yellow GaP 570 160 30 — — — —
Green GaP 565 140 24 GaN 520 1,200 45
Turquoise — — — — GaN 495 2,000 30
Blue — — — — GaN 465 325 45

TABLE 1.3 Comparison of Chip Technologies for Wide-Angle Non-Diffused LEDs
(See also color insert.)

1.13.2 LED White Light
When light from all parts of the visible spectrum overlap one another
(Fig. 1.12), the additive mixture of colors appears white. However,
the eye does not require a mixture of all the colors of the spectrum to
perceive white light. Primary colors from the upper, middle, and
lower parts of the spectrum (red, green, and blue), when combined,
appear white. To achieve this combination with LEDs requires a
sophisticated electrooptical design to control the blend and diffusion
of colors. Variations in LED color and intensity further complicate
this process.
Presently, it is possible to produce white light with a single LED
using a phosphor layer (Yttrium Aluminum Garnet) on the surface of a
blue (Gallium Nitride) chip. Although this technology produces various
hues, white LEDs may be appropriate to illuminate opaque lenses or
backlight legends. However, using colored LEDs to illuminate similarly
colored lenses produces better visibility and overall appearance.

FIGURE 1.12 Photometer
The structure of
an LED to produce Iv (mcd)
a mixture of light:
white light.
LED