The Festival of Lights on the River
Energy & Light Technology

The Festival of Lights on the River

Floating lamps — the science of light and energy.

Energy & Light Technology12-Month Curriculum 12h

The Story

The Night of Lamps

Every year in the month of Kati — October in the English calendar — the people of Assam celebrate Kati Bihu, the quietest and most beautiful of the three Bihus. There are no feasts, no dancing. Instead, families light earthen lamps and place them at the foot of tulsi plants, on granary posts, and — in the river villages — on the waters of the Brahmaputra itself.

The lamps are small clay diyas, no bigger than a child's palm, filled with mustard oil and a cotton wick. When lit, they glow like tiny golden hearts. And when they are set on the river, the Brahmaputra becomes a road of flickering stars.

In the village of Nimati, near the ferry ghat that connects the mainland to Majuli, a boy named Hriday was preparing his lamp for the festival.

The Wish

Hriday was ten years old, and this was his first year making his own lamp. His mother had taught him how to shape the clay, smooth the edges, and press a small channel for the wick. His lamp was simple — not as elegant as his mother's, not as sturdy as his father's — but it was his.

"What will you wish for?" asked his little sister, Mrinmoyee, who was six and believed that the lamp carried your wish to wherever the river took it.

Hriday thought carefully. Last year he would have wished for a cricket bat or a bicycle. But this year, something different was on his mind. His best friend, Pankaj, had moved away when his family relocated to Guwahati for work. The empty seat next to Hriday in school felt like a hole in the day.

"I wish for Pankaj to remember me," said Hriday. "Even though he's far away."

Mrinmoyee nodded solemnly. "That's a good wish. The river will carry it."

The Floating

At dusk, the whole village gathered at the ghat. Hundreds of families, each carrying their small clay lamps, each lamp holding a wish. The Brahmaputra stretched before them, dark and vast, its surface smooth as silk in the windless evening.

One by one, the families lit their wicks and placed their lamps on the water. Hriday's mother placed hers first — a prayer for a good harvest. His father placed his — a prayer for the family's health. Mrinmoyee placed hers, whispering her wish so quietly that even the river had to lean in to hear.

Then it was Hriday's turn. He knelt at the water's edge, cupped his lamp in both hands, and lit the wick. The flame caught immediately — steady, bright, confident, as if it knew where it was going. Hriday placed the lamp on the water and gave it a gentle push.

"Find Pankaj," he whispered.

The Journey

Most lamps drifted a few hundred metres before their wicks burned out or the current tipped them over. By midnight, the river was dark again, littered with spent clay cups bobbing in the shallows.

But Hriday's lamp kept going.

It caught the central current — the strong, deep flow that runs down the middle of the Brahmaputra like a highway. The flame burned steady, protected by the slightly raised rim that Hriday had shaped by accident when his thumb slipped during the making. That imperfect rim acted as a windbreak, shielding the flame from the breeze.

The lamp floated past Nimati. Past the Majuli ferry route. Past the sandbars where fishermen slept in their boats. Past Jorhat, past Kaziranga, past Tezpur. The flame burned on, fed by the mustard oil, sheltered by the crooked rim, carried by the river that seemed to know where it was going.

Nobody saw this, of course. A tiny lamp on a vast river at night is invisible to everyone but the stars. But the river knew. The Brahmaputra, old as the Himalayas, carries many things — water, silt, fish, stories. One more lamp was nothing to carry. And the wish inside it was the kind the river understood: the wish to stay connected.

The Arrival

In Guwahati, a hundred and fifty kilometres downstream, Pankaj couldn't sleep. He was homesick — not for the village exactly, but for the river, the ghats, the sound of water against the ferry's hull, and most of all for Hriday.

He walked to the Fancy Bazaar ghat at dawn, just to watch the river. And there, caught in the reeds at the water's edge, was a small clay lamp. Its wick had finally burned out, but the lamp was intact — a simple, slightly crooked diya with a thumbprint on one side and a raised rim that looked like a smile.

Pankaj picked it up. He didn't know where it had come from. He couldn't know that it had travelled all night from Nimati, carrying a wish with his name on it. But he turned the lamp over in his hands and felt something — a warmth that had nothing to do with the morning sun. A feeling of being remembered.

He took the lamp home and placed it on his windowsill. And that evening, he wrote a letter to Hriday — the first of many — that began: "I found something in the river today, and it made me think of you."

The people of Assam say that during Kati Bihu, the Brahmaputra isn't just a river. It's a postman. It carries lamps and wishes from one heart to another, connecting people who are separated by distance but not by love. And if your lamp travels farther than anyone else's, it means the river heard your wish — and decided it was worth delivering.

The end.

Try It Yourself

Choose your level. Everyone starts with the story — the code gets deeper as you go.

Story Progress

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Ready to Start Coding?

Here is a taste of what Level 1 looks like for this lesson:

Level 1: Explorer — Python
import numpy as np
import matplotlib.pyplot as plt

# Energy efficiency of light sources (lumens per watt)
sources = ["Oil lamp", "Incandescent", "CFL", "LED"]
efficiency = [0.3, 15, 65, 120]  # lumens per watt

plt.figure(figsize=(10, 5))
bars = plt.bar(sources, efficiency, color=["#f59e0b", "#ef4444", "#a855f7", "#22c55e"])
plt.ylabel("Lumens per Watt")
plt.title("Light Source Efficiency: From Oil Lamps to LEDs")
for bar, val in zip(bars, efficiency):
    plt.text(bar.get_x() + bar.get_width()/2, bar.get_height() + 2,
             f'{val}', ha='center', fontweight='bold')
plt.grid(axis='y', alpha=0.3)
plt.show()  # How many times more efficient is an LED than an oil lamp?

This is just the first of 6 coding exercises in Level 1. By Level 4, you will build: Compare Light Source Efficiency.

By Level 4, enrolled students build: Compare Light Source Efficiency

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