CHAPTER 10 ■ LEDSToday, colored lenses remain the most common and least expensive. However, with the technological
improvements in brightness, the trend is heading toward very lightly tinted water clear and diffused.
LED Viewing Angles
It’s valuable to know the viewing angle characteristic of a particular LED, as it gives you a sense of how
the light beam will spread out. A large viewing angle indicates an LED that is more visible from the sides.
Datasheets often show the viewing angle in graph form, which is much more informative than a single
number.
Only clear lens LEDs are described with viewing angles, since the color-diffused or white-diffused
lenses naturally distribute the light throughout the entire LED.
LED Colors
LEDs became available in commercial production quantities in the 1970s, beginning with the color red. The
1990s marked significant improvements in brightness and efficiency, as well as the introduction of a pure,
affordable blue. High-quality white LEDs appeared about that same time because they’re really blue LEDs
with white-emitting phosphor.
Red, orange, yellow, and yellow-green remain the least expensive. True green, blue, and white have
come down in price, but can still be more expensive than the price of red. Violet and ultraviolet are also
available.
LEDs emit most of their light in a narrow band of color. As such, mixed colors like brown would
necessitate multiple dies that are finely tuned. That would be a difficult feat to consistently replicate in
production quantities. It will be a while before there’s a selection of colors resembling a case of crayons
(“burnt umber?”). See Figure 10-7 for what’s available now.
Relating Color to a Wavelength
In advertisements and datasheets, LED color is often described by a dominant wavelength measured in
nanometers (nm). Sometimes this is referred to with the abbreviation lP, for peak wavelength.
When the wavelength of an LED is indicated, use Table 10-1 to see where the color lies within the range.
For example, 655 nm is a good red, but 635 nm looms a bit towards orange. (This is fine, if orangish-red is the
color you desire).
Figure 10-7. A spectrum of colors from infrared to blue, with white on the end. (This image isn’t particularly
helpful in a grayscale book. But, trust me, it looks lovely.)