http://www.navweaps.com/Weapons/WNUS_Radar_WWII.htm
It would seem to me that before 1942, radar of any type
was very rare in US service and was only installed on most ships in response to the events of December 1941.
It's also worth noting that WWII did not start in December 1941 - for most of the world it was several years earlier when the Germans were annexing their neighbours. For Japan's neighbours it was even earlier, almost a generation in China's case (Japan's invasion of Manchuria in September 1931).
As the Pacific theatre after the fall of Singapore was mainly fought by the US (but not forgetting many smaller nations such as Australia and New Zealand), it seems appropriate to leave out radars possessed by countries not directly involved in the region when discussing Japanese naval technology.
Something else worth pointing out is that the US had access to British and other allied nations research into radars and fire control. The Japanese were essentially on their own. Should the Japanese have had similar advances in technology available to them, the war at sea may have been much more bloody (as if the actual number of deaths weren't enough).