Like millions of others, I downloaded the myLite iPhone app. For the few times I've used it, the iPhone-as-flashlight has worked OK. However, since this is not an app I tend to use very much, it isn't on my front page - nor is it on the second. As such, when I need the flashlight I've got to first find the app and then wait for it to boot. Enter Mail.
By default, the Mail app is on the front page (I couldn't move it off the front page if I wanted as it's part of the iPhone layout) and when launched (at least to my eyes), emits a comparable amount of light to the myLite app (plus, it boots a lot faster too).