A good way of extending an ember (or solar lighting) or catching a spark is using a King Alfred Cake (cramp ball fungus or Daldinia concentrica). A King Alfred Cake is a fungus which grows on dead Ash trees, and when the fungus has died off, they turn black and act like a coal. Only collect them when they have turned black (dead) , not brown (still alive). If dead they should come off the dead tree quite easily - you may need to prise them off using a knife. You can store for a very long time as long as there is no moisture otherwise they will go mouldy!
You need to strike the sparks\add the ember\direct the sunlight onto the underside not the smooth outside of the ball. It only takes a small spark (or ember) to light. You will know when it is lit, as you will see a small red glow. Blow on it and the ember will get larger and it will burn like a coal. You can then place your dry tinder on top, such as dry clematis bark or dead dry grass or bracken. Blow onto the glowing ember, and keep blowing, it will start to smoke and may produce lots of smoke! Keep blowing until the tinder bursts into flame then place your kindling on top.
They will smoulder for quite a long period of time so is a good way to extend an ember if the tinder is damp or you're not quite prepared!