The one with rays of light emanating from the sun is most commonly associated with Japan AT WAR, while the simpler red-circle-on-plain-white-background is more commonly associated with peacetime Japan. Interestingly, both flags are somewhat unpopular within Japan. In fact, some public schools even refuse to fly either version, on the grounds that the national flag somehow promotes nationalism, wartime feelings, and the desire to do some empire-building. These days, within Japan, the only people flying the flag-with-light-rays are the ultra-right-wing nationalists known colloquially as "the black bus guys", because of their penchant for driving around in large black buses, blaring nationalistic anthems from huge speakers. These folks want to reinstall the emperor as sole political leader of Japan, end Japan's reliance on US armed forces, start rebuilding their own army, and very possibly start colonizing neighbors. They're not at all popular-- strictly a fringe group. In general, I think you can safely liken Japan's two flags to the US's tendency to name the SAME department "war department" or "department of defense", depending on whether the US is currently at war. Or, you might feel more safe likening the two flags to Germany's current flag & the WWII swastika flag: same country, 2 VERY different attitudes.