LUX - Light Meter

Overview

An iOS app that measures ambient brightness in lux using the camera. Open it and start measuring right away.

Story

I keep houseplants at home, and when deciding where to put them I wanted to know whether a spot actually got enough light. Before buying a dedicated light meter, I looked for an app that could measure it with my phone.

The ones I found were packed with features but never ready to measure the moment I opened them. I had to hunt for the right button, and no matter how often I used them the steps never stuck. It felt like this could be simpler. Building it myself was an option, so I did.

There was no grand problem behind it. I wanted a light meter I found easy to use. That was the reason.

The first thing I decided was that it had to be measuring the instant it opened. The initial release did nothing but read illuminance. Features have been added since, and that one point has not changed.

After launch, an in-app survey collected 175 responses. Plants were the most common use, same as mine — but people were also checking reading light, running school science projects, setting up party lighting, teaching classes, and working in healthcare and elder care. Uses I never imagined when I built it, taught to me afterward.

The problem it solves

You don’t always have a dedicated light meter on hand, but you often want a number instead of a guess. Is the desk lamp bright enough? Is there enough light for this shot? Are the plants or the aquarium getting what they need? LUX turns that judgement into a reading you can take with the iPhone already in your pocket.

Illuminance is calculated from the ISO sensitivity and exposure duration reported by the camera. Everything is processed on-device — nothing is sent anywhere.

It measures the moment you launch it, holds a value on tap, reads color temperature (CCT / Kelvin), and records the minimum, average, and maximum lux of a session. Readings can be switched to foot-candles (fc). Premium adds measurement history, CSV export, and PPFD for plant lighting.