🌞 Build a Smart Brightness Controller with HarmonyOS and Ambient Light Sensor (SmartLux)

#huawei #harmony #harmonyos

Read the original article：🌞 Build a Smart Brightness Controller with HarmonyOS and Ambient Light Sensor (SmartLux)

SmartLux with ArkTS (This picture was generated by AI)

🧠 Introduction

Have you ever been blinded by your screen in a dark room, or struggled to see anything under sunlight? Manually adjusting screen brightness can be annoying and inconsistent. That's where SmartLux comes in — a HarmonyOS wearable app that automatically adapts screen behavior to ambient light using ArkTS and sensor services.

In this article, we'll build a HarmonyOS app that reads real-time lux levels from the ambient light sensor and dynamically adjusts the UI theme and optionally screen brightness.

By the end, you'll have:

Hands-on experience with SensorServiceKit
A functional HarmonyOS UI that reacts to environmental light
(Bonus) Background task setup for persistent monitoring

Let’s glow 🟡

⚙️ What We'll Use

What we'll use and why

📦 Project Setup

Create a HarmonyOS Stage project with ArkTS
Set deviceType to wearable or phone
Open module.json5 and add the following permissions:

"requestPermissions": [
  { "name": "ohos.permission.KEEP_BACKGROUND_RUNNING" },
  { "name": "ohos.permission.RUNNING_LOCK" }
]

💡 Setting Up Ambient Light Sensor

We'll use sensor.on to continuously monitor the ambient light levels.

sensor.on(sensor.SensorId.AMBIENT_LIGHT, (data: sensor.LightResponse) => {
  const lux = data.intensity
  console.info('💡 Lux value: ' + lux)
}, { interval: 100000000 })

🎨 Dynamic UI Theming Based on Lux

private getThemeColor(): Color {
  if (this.lux < 50) return Color.Black
  else if (this.lux < 500) return Color.Gray
  else return Color.White
}

private getTextMessage(): string {
  if (this.lux < 50) return '🌑 Dim environment...'
  else if (this.lux < 500) return '🌤️ Light level is moderate.'
  else return '☀️ Bright as daylight!'
}

🔆 Brightness Calculation (Optional)

let brightness = Math.round((lux / 1000) * 100)
brightness = Math.max(10, Math.min(100, brightness))

⚠️ Limitation

@system.brightness.setValue() only works for system apps starting from **API 7**. In third-party apps, use it only for internal logic or visual feedback.

const info: wantAgent.WantAgentInfo = {
  wants: [{ bundleName: this.context.abilityInfo.bundleName,
  abilityName: this.context.abilityInfo.name }],
  operationType: wantAgent.OperationType.START_ABILITY,
  requestCode: 0,
  wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
}

const agent = await wantAgent.getWantAgent(info)
await backgroundTaskManager.startBackgroundRunning(this.context,
backgroundTaskManager.BackgroundMode.DATA_TRANSFER, agent)

🎬 Demo

👋 Conclusion

SmartLux shows how easy it is to create responsive, environment-aware apps with HarmonyOS and ArkTS. With just a few APIs and sensors, you can make your UI adaptive, energy-efficient, and user-friendly.