Why do optical mice always use red lights?

It’s crazy to think that the mouse, a gadget synonymous with the computer, was invented while the Beatles were still together. The prototype first saw the light of day in 1968, and a few iterations later, it became the go-to input method for computer experts everywhere. Even today, when you compare a mouse to a laptop touchpad, the “old reliable” is faster, more precise, and in many cases, just plain more comfortable.

Although using a mouse is second nature to many, there are still some cool things you can do with a mouse that you may not be aware of. But that’s not where the mystery ends. Flip your optical mouse over and watch the light flicker. There is a good chance that this light will be red. Is there a particular rhyme or reason behind the choice of color? Why do optical computer mice always seem to use red lights?

Believe it or not, this comes down to two things: slightly better operation and lower cost. Optical mice use a tiny LED diode to reflect light off the surface they are resting on, then a CMOS sensor, usually silicon-based, collects the reflected light. Since red may be easier for silicon sensors to detect than shorter wavelength colors like blue, this may help the mouse detect small movements a little better. Of course, this is not to say that different colored diodes don’t work, but red diodes are plentiful and, more importantly, quite cheap. So in a sense, going blue, let’s say, would be overkill (looking at you, Microsoft).

Despite their affordable price, optical mice are actually quite high-tech. Think of a mouse as a primitive camera that takes thousands of images of your desktop in a single second. The aforementioned CMOS sensor then sends them to a DSP, which detects whether the patterns have changed in an image sequence. It analyzes where and how far the mouse moved, and voilà, your computer translates all that into cursor movements. Although the red light is more “reflective”, it is not a rule that cannot be broken.

For example, a Reddit user changed the LED on his mouse to blue. One commenter pointed out that the sensor likely wouldn’t register movements on orange or yellow mousepads. Still, the person who started the thread said it worked well, even on these particular surfaces. And it’s not just players who make unnecessary mods. Even Microsoft experimented with a different color diode in its BlueTrack mouse, claiming that a blue light could provide higher contrast.

Ultimately, this doesn’t have a major impact on mouse performance, and so it doesn’t justify the cost of straying from what is considered a standard. This is why most optical computer mice are red: if it’s not broken, don’t fix it. This is especially true if it will make the final product even slightly more expensive to produce at a time when some gadgets are seeing price hikes due to supply shortages.