Millions of iPhone and iPad users rejoiced after an open source iOS version of f.lux was available for downloading without jailbreaking. But the pleasure of side-loading the app did not last for long as Apple shut the doors on f.lux for iOS devices. In its defence, the Cupertino-based tech giant said the iOS version of f.lux violated the Developer Program Agreement (nobody wants to embroil into legal feuds with Apple), forcing the developers to pull down the download link.

For those who are unaware, f.lux is a popular programme that helps users adjust a computer screen's colour and brightness to reduce strain on eyes, especially at night. The tool received a good response when it debuted on iOS. According to the f.lux blog post on Thursday, the iOS download page was visited 176,000 times in just 24 hours. The short-lived popularity of f.lux on iOS was due to the fact that it was made available to iPhones without jailbreaking them.

"Apple has contacted us to say that the f.lux for iOS download (previously available on this page) is in violation of the Developer Program Agreement, so this method of install is no longer available. We understood that the new Xcode signing was designed to allow such use, but Apple has indicated that this should not continue," f.lux blog post reads.

One can gauge the popularity of f.lux as PC users have downloaded the app over 15 million times.

Will this popularity help f.lux gain a back-door entry to Apple iPhones and iPads? The blog post hints that several attempts over the years have failed. F.lux is encouraging its faithful fans to send a feedback to Apple urging it to allow f.lux operations through Documented APIs.

"f.lux cannot ship an iOS App using the Documented APIs, because the APIs we use are not there. In the last 5 years, we have had numerous conversations with Apple about our product and what would be required to make it work with iOS," the company said.