Hebrews 10:19-25; Ps 24(23):1-2. 3-4b. 5-6; Mark 4:21-25
What is going to happen if you put a candle under a bed? Quite a lot of light perhaps - to say nothing of heat and smoke! At least the lamp would not go out, unlike the one put under a bowl.
In both cases clearly the purpose of the lamp has been usurped, and something unintended has happened. So - the light is usually understood to be the love and life of Christ - something we are each given at Baptism, and should preserve and use to illuminate our way through life. Both of the parable's scenarios for our life can happen - the enthusiasm of youth can lead to conflagration, excessive modesty can lead to being unable to share the joys of life.
There is a middle ground and when one finds it then ones' light is made available to share with others. Remember also, when your light ignites another's dormant lamp, the you now have twice as much lamplight between you!