阅读答题。
                                                                                                        长相思·雨
                                                                                                           万俟咏
                                                                             一声声，一更更。窗外芭蕉窗里灯，此时无限情。
                                                                             梦难成，恨难平。不道愁人不喜听，空阶滴到明。

夏天的傍晚，萤火虫在树丛间飞舞，点点荧光非常好看。这是因为萤火虫释放的能量一部分转化成了（  ）