Chen Hao stood by the wall, holding half a cookie in his hand. He looked up at the sky; the sun was already setting, casting a long shadow.

He popped the biscuit into his mouth, chewed a few times, and swallowed. Then he lifted his foot and tapped it lightly twice on the wall. The sound was muffled, like hitting an old wooden crate.

“This wall is too plain,” he said.

Nana walked up from behind, her optical lens scanning the wall. "Do you have any specific ideas?"

“Make it bright,” Chen Hao said. “At night, anyone who gets close will be able to see it. Not just see it, but scare them.”

Susan, carrying a stack of circuit diagrams, came out of the main control area and stopped upon hearing this. "More stuff to add?"

“It’s not something I added randomly.” Chen Hao turned to face her. “You remember that tremor in the northwest corner last time, right? It was pitch black, the cameras couldn’t capture it, and the sensors didn’t react. If someone had come near us, we wouldn’t have even seen their shadow.”

Susan frowned. "Installing lights is fine, but don't alter the structure. The other day the wind was so strong that a section of the wall plaster cracked."

Carl came over carrying a shovel and chimed in, "Where to run the wires is also a problem. Burying them in the ground risks dampness, and sticking them to the wall risks sun exposure."

Nana's eye light flickered. "Modular installation is recommended. Lighting components should be secured with lightweight brackets, avoiding load-bearing seams. Wiring should be run underground in conduits, and the joints should be sealed."

Chen Hao grinned. "Listen to this, Miss Robot has even figured out how to hide the wires."

"What about the power supply?" Susan asked. "The main power supply is barely holding up right now. If the kitchen refrigerator starts up again, the voltage across the entire North District will fluctuate."

“No main power is needed,” Nana continued. “We can use recycled solar panels, with independent circuits. There are seventeen old photovoltaic panels in the waste pile on the east side of the base, at least six of which still have basic power generation capabilities.”

Carl scratched his head. "That thing still works?"

“It needs to be tested and modified,” Nana said, “but it’s highly feasible.”

Chen Hao clapped his hands. "Then it's settled. Let's give the wall a cover with lights, so it can absorb electricity during the day and glow at night. Add some reflective strips, and we can even make it a rainbow wall."

Susan sighed. "You really think this is like renovating a neighborhood garden?"

"Pretty much." Chen Hao shrugged. "The difference is that here, there might be some non-vegetarians squatting outside the garden."

Susan didn't speak, but looked down and flipped through the drawings in her hand. "If we're going to use a separate circuit, I can plan the wiring path. But we need to confirm the bracket anchor points first, so as not to affect the stability of the wall."

“I’ll be in charge of the structural assessment,” Nana said. “Local modeling can be completed in three minutes.”

"Then hurry up and calculate," Chen Hao urged. "I want to try the first section tonight."

Half an hour later, the four of them gathered at the southeast corner of the wall. Nana projected a 3D model, with several small squares distributed on the wall, like a row of tiles.

“This is the layout of the lighting modules,” she said. “There are 12 groups every 5 meters, covering the entire length. The brackets are at an angle of 11 degrees to the wall, minimizing stress. The solar panels are installed on the outer edge of the top of the wall, with an angle of 34 degrees calculated based on local sunshine.

Susan stared at the model for a while. "How do you make the interfaces waterproof?"

“Double-layer silicone sealing rings, plus a drainage channel design,” Nana replied, “so rainwater won’t accumulate.”

Carl crouched down and gestured with his hands. "Shall I go find solar panels at the east rubble heap now?"

“I’ll go with you.” Susan put away the blueprints. “We can also see if there are any usable insulating tubes.”

Chen Hao rubbed his hands together. "When you come back, I'll draw lines on this section of the wall to mark the location."

After the two left, Chen Hao took out a marker and drew an X on the wall. Nana stood beside him, the camera constantly adjusting its focus.

"Do you think this plan will work?" he asked.

“The probability is 89.3 percent,” Nana said. “The main risk comes from the uncontrollable degree of material aging.”

"That's high enough," Chen Hao laughed. "Much higher than my exam passing rate."

As evening fell, Carl and Susan returned, dragging three tattered suitcases. Inside were six solar panels, all chipped at the edges and covered in dust.

Nana tested the output power of each component and selected three effective ones. Then she disassembled an old mobile phone charging module and removed the voltage regulator chip inside.

“It’s usable,” she said. “It can be easily modified to match the LED drive voltage.”

Susan took the tools and began soldering the circuitry. Carl, on the other hand, sanded the bottom of the bracket to prevent rust.

Before it got completely dark, they installed the first lighting system at the base of the southeast section of the wall. A ten-meter-long LED light strip was embedded in an alloy groove and connected to a slanted solar panel.

Nana pressed the start button.

The lights came on, casting a blue-white halo on the ground, clearly showing the base of the wall. A mouse darted out of the grass, its shadow stretched long.

Chen Hao stared at the ground. "Not to mention people, even a cockroach will become visible when it crawls by."

"The uniformity of illumination is good." Nana recorded the data. "The current brightness is 120 lumens, and the power consumption is 3.2 watts."

Susan inspected the junction box. "The seal is fine, there's no leakage."

Carl stood at a distance and looked around. "It's a bit deserted. Should we add some more color?"

"You want to set up neon lights?" Chen Hao laughed.

“That’s not what I meant,” Carl scratched his head. “It’s just…it looks too much like a hospital corridor. Could you change to warmer lighting? Or perhaps change the color every few meters?”

Nana responded: "The LEd model can be adjusted. If using RGb light strips, a nighttime gradient mode can be set through the program, which has both warning and psychological comfort functions."

"Psychological reassurance?" Chen Hao raised an eyebrow. "Does this place even need reassurance?"

"Being in a high-pressure environment for a long time and having monotonous visual stimulation can easily trigger anxiety," Nana said. "Soft color changes can help relieve tension."

Susan nodded. "That makes sense. Since it's all about modifying the circuit anyway, soldering on a few more resistors won't be a problem."

"Let's do something fancy," Chen Hao said. "During the day, it's a defensive fortification; at night, it becomes a light show. Let people outside think we've opened a nightclub."

The next morning, Chen Hao walked along the wall with a marker, marking an X every five meters. Nana followed behind, constantly adjusting the position.

Susan and Carl began cleaning the dust off the remaining solar panels in preparation for the next installation.

Chen Hao stopped drawing when he got to the fifth mark.

“The ground here is a bit loose,” he said.

He bent down, grabbed a handful of soil, and rubbed it between his fingers. "It didn't rain a few days ago, why is it so soft?"

Nana crouched down and extended her probe arm close to the ground. "The soil moisture is 23 percent higher than the surrounding area. There are slight signs of subsidence."

"Is it related to what happened in the northwest corner?" Chen Hao asked.

“The correlation cannot be determined,” Nana said, “but we recommend strengthening monitoring in this section.”

"Let's install the lights first." Chen Hao stood up. "It's better to have something on than something dark."

They continued working. Before noon, the second lighting system was assembled.

When the power was turned on for testing, one of the brackets made a slight "click" sound as soon as the light came on.

Carl rushed over immediately. "The screw is loose!"

He tightened the fasteners and reinforced it again with a wrench. "This wall can't hold up; we need to replace it with a shorter anchor."

“The installation parameters have been updated,” Nana said. “The subsequent brackets will be shortened by 3.7 centimeters to reduce the pressure on the wall.”

Susan wiped her sweat. "We can only install these two sets today. The rest of the boards still need repairing; two of the terminals are severely oxidized."

"That's enough." Chen Hao looked at the two sections of wall that were lit up. "At least tonight, we can see the path under our feet during patrol."

He walked to the lamp and looked up at the top of the wall. The solar panels reflected the sunlight like a row of small mirrors.

“We’ll add a number to each section of the light strip,” he said. “And we’ll add a switch so we can turn on whichever section we want.”

“Remote control is possible,” Nana said. “The module can be turned on and off independently via wireless signal.”

“That’s even better.” Chen Hao laughed. “If anyone dares to come near at night, I’ll light up that whole section and make it as bright as day.”

Susan packed up her toolbox. "Assuming there are no more power supply problems."

"Don't worry." Chen Hao patted her shoulder. "This time we won't touch the main power source. If we explode, we'll only explode the solar panels."

At 3 p.m., the four were still busy by the wall. Chen Hao was recording the installation progress on a tablet, while Nana updated the circuit diagram in real time.

Susan and Carl carried the remaining materials into the makeshift shed. The shed was set up inside the fence and was filled with cables, supports, and tools.

Chen Hao stood beside the newly installed LED strip lights, drawing a route on his tablet with a marker. His finger swiped across the screen, stopping at the soft ground in the northwest corner.

Nana walked over. "What are you thinking about?"

"That piece of land," Chen Hao said, "I want to go see what's there when the lights are on tonight."

He looked up at the overgrown weeds outside the wall. The wind blew, and the tips of the grass swayed.

A crow flew in from a distance and landed on the solar panel on the top of the wall.