A humidifier for a fuel cell is provided. Consistent interfaces are generated from the business object model. Then, the lamp is operated at DC current, and the current magnitude is reduced further, thus achieving a lower dimming level. The solar chimney may be equipped with both internal and external solar collectors, operating in parallel. In the fluorescence observing apparatus, a GaN semiconductor laser is employed as the light source. Wherein the first coefficient of thermal expansion is greater than the second coefficient of thermal expansion.