---
title: "How Sensors & Pixels Capture Light"
canonical: https://stackingstarlight.com/start-here/sensor-and-pixels
description: "A camera sensor is a grid of pixels that count photons by accumulating electrons, then convert them to numbers via an ADC."
---

# How Sensors & Pixels Capture Light

> A camera sensor is a grid of pixels that count photons by accumulating electrons, then convert them to numbers via an ADC.

Each pixel is a well that fills with electrons as photons strike it (the photoelectric effect). At the end of an exposure the charge in every well is read out and digitized by an analog-to-digital converter (ADC) into a number (ADU). Key properties: **quantum efficiency** (fraction of photons converted), **full-well capacity** (before saturation), **read noise** (added each readout), and **bit depth** (ADC levels). These set how faint a signal you can record and how cleanly.

---

Source: [https://stackingstarlight.com/start-here/sensor-and-pixels](https://stackingstarlight.com/start-here/sensor-and-pixels) · Part of [Stacking Starlight](https://stackingstarlight.com) by Michael Kalika.

LLM resources: [LLM index (llms.txt)](https://stackingstarlight.com/llms.txt) · [Complete LLM text (llms-full.txt)](https://stackingstarlight.com/llms-full.txt) · [Markdown homepage (index.md)](https://stackingstarlight.com/index.md)