LEDs don't inherently produce yellow light in the same way that a yellow crayon contains yellow pigment. Instead, they create yellow through a combination of techniques:
Additive Color Mixing
The most common method uses additive color mixing. This principle, as stated in one of the provided references, shows that green + red = yellow. RGB LEDs contain separate red, green, and blue LEDs. By simultaneously activating the red and green LEDs at specific intensities, you can produce a range of yellows and yellow-orange colors. The relative brightness of the red and green LEDs determines the exact shade of yellow.
Phosphor Conversion
Another technique involves phosphor conversion. White LEDs, which are very common, often use a blue LED chip coated with a phosphor material. This phosphor absorbs the blue light and re-emits it at longer wavelengths, including yellow and green, resulting in a white light appearance. If the phosphor is carefully selected to emphasize yellow emission, it will appear as a yellow-leaning white, or even a relatively pure yellow depending on the desired color point. Some commercial LEDs are engineered specifically for yellow output using this principle.
Filters
A less common method involves placing a yellow filter over an existing LED, whether it's red, green, or white. The filter absorbs unwanted wavelengths of light, allowing only yellow light to pass through, resulting in a generally less efficient yellow light. The color saturation and purity will largely depend on the filter's quality.
Examples
- RGB LED Strip Lights: Many RGB LED strip lights use additive color mixing to create yellow. The manufacturer can easily adjust the blend of red and green in their LED chips.
- Amber LEDs: While not strictly "making yellow," amber LEDs produce a yellow-orange hue through a phosphor-based approach similar to white LEDs.
It is important to note that RGB LEDs struggle to create the full spectrum of yellow due to limitations in the precision and consistency of the color mixing process and the inherent color of their red and green LEDs. The resulting yellows can sometimes appear greenish, depending on the specific LED and control.
