i can't solve a riddle

Is it a candle? Or something that lights up...a light bulb.

I think it is coal, what's your opinion? Originally it is black and when ignite it, then it becomes to burn.inconvenient time? i think when we encounter some difficulties,like cold,hungry or other, we always say their is no hope and our future is so dark that have to give up! so coal and its light give our hope!

Reading by the glow... When it is dark, I am cold. When it is light, I am hot. My life ends at the most inconvenient time. fireplace? campfire?

The Cowardly Lion I am born in fear, raised in truth, and I come to my own in deed. When comes a time that I'm called forth, I come to serve the cause of need. What am I? "Courage"

I don't know unless it might be "The Sun"???? Of course the sun never really get's cold, so I don't know. What about a light bulb? It gets really warm when it's turned on. The more I think about it the more I think that's right...the light bulb.