# A Photic Lexicon

For an autonomous truck, light is a dialect. It is not merely a tool for punching a hole in the darkness so a human driver can see the road ahead. Instead, light is an active form of speech, a constant chatter of inquiry and declaration directed at two entirely different audiences: the fragile, unpredictable humans outside the cab, and the silicon brain within. The visible glow is a translation, a clumsy attempt to convey a sliver of the machine's internal monologue, while an invisible torrent of light is the machine's primary method of perception.

Walk near a self-driving truck and you might see it try to talk to you. Not with a horn or a synthesized voice, but with a turquoise glow. Waymo Via, the company's trucking division, has experimented with this particular hue on its external light bars to signal its state of being. A solid glow might mean it has detected a pedestrian and is waiting. A soft pulse could signal its intent to proceed. Daimler's trucks, in partnership with Torc Robotics, have been tested with similar blue-green light bands to indicate when the autonomous system is engaged. This is an attempt at etiquette. A machine trying to make eye contact.

The difficulty is that there is no shared dictionary for this new language. Each manufacturer is inventing its own grammar of colour and rhythm. What a solid turquoise bar on a Waymo truck means may be entirely different from a blinking blue light on another company's rig. This creates a disquieting ambiguity on the road. Humans rely on a subtle, unwritten code of nods, waves, and headlight flashes to negotiate four-way stops. The trucks are attempting to join that conversation, but each is speaking a private, corporate-developed dialect. A language with no Rosetta Stone.

The Unseen Spectrum

Most of the light a self-driving truck uses is completely invisible to the human eye. The most critical sensory organ is LiDAR, which functions by emitting constant, rapid-fire pulses of laser light, typically in the near-infrared spectrum. It is a constant exhalation of invisible energy. Each pulse bounces off an object—a tyre scrap on the tarmac, a deer on the verge, the reflective stripes of a lane marker—and returns to a sensor. By measuring the time it takes for the light to return, the system builds a dense, three-dimensional map of its surroundings, a "point cloud" of staggering detail. It's how the truck feels the shape of the world.

This unseen light has its own technical nuances. Many systems use lasers at a 905-nanometer wavelength, while others use 1550-nanometer lasers. The distinction matters. The 1550 nm wavelength is absorbed by the human eye's cornea and lens rather than reaching the retina, which allows manufacturers to use more powerful lasers without posing a safety risk. More power means a longer range, allowing the truck to perceive objects from further down the highway. At the same time, the truck's conventional cameras still rely on the grubby, familiar world of visible light, needing the truck's own powerful LED headlamps to cut through rain and gloom. Another kind of eye, the thermal camera, sees a different spectrum entirely: the infrared glow of heat radiating from a living body.

The Grammar Problem

The core confusion is one of translation. The truck's processing unit makes a decision based on millions of incoming data points from LiDAR, radar, and cameras. It might conclude, "Based on the trajectory of the vehicle in the adjacent lane and the slight shimmer on the road surface indicating potential ice, I will reduce my speed by 4% and increase my following distance by 12 metres." The challenge is then to communicate that complex, probability-based decision to a human driver in a split second. How do you say all of that with a coloured light? The nuance is lost.

This creates a communication gap that is both technical and legal. Many jurisdictions have stringent regulations on the colours of lights a vehicle can display. Flashing blue and red are reserved for emergency services; amber for service and hazard vehicles. A self-driving truck glowing turquoise sits in a regulatory void. Is it providing information, or is it just a distraction? The established semaphore of the road is being interrupted by a new, uncertain signal. The truck broadcasts its intentions constantly, a monologue of photons, but whether anyone truly understands what it is saying remains an open question.