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Using low-gain DMSP data, we obtained absolute values of light energy loss ejected to space from different cities. Showing these data to local people in each city encourages them to try to reduce light energy loss. This educational approach is very effective in reducing light pollution.

We are now developing a system to estimate light energy loss to space using the US DMSP (Defense Meteorological Satellite Program) data and obtained many interesting results. The satellites have solar synchronous orbits with altitude around 800 km, and continuously obtain absolute (well-calibrated) flux ofterrestrial surface light. City light ejected to space is mostly energy loss because the light is not used to illuminate objects to be seen or decorated. The total amount of its energy loss in Japan estimated by us is an order of 20 billion yen (about 200 million US dollars). We are now estimating its loss for each cities (or areas) in Japan and in the world. Further, we found a possibility to estimate energy usage of each country after obtaining a clear relation between light energy loss and electric energy usage within different areas ofindividual electric companies in Japan. Therefore, we would like to conclude that our continuous estimation of city light from space are and will be creating a global information of energy usage.