• The characteristics of the solar cell should be measured in sunlight also if possible; in this case both direct and diffused light are involved.
• The thermophile is used again to determine the relationship between the shortcircuit current and the light intensity, although it measures only direct light because of its small angular aperture. For comparative purposes, therefore, we must support a black cardboard tube about 20 cm long in front of the solar cell to screen it from the diffused light. It is important that the thermopile and the solar cell are pointing directly into the sun.