Since Newton specified rainbow colors in 1672, we have been told that a rainbow has 7 colors : red, orange, yellow, green, blue, indigo and violet. These colors are thought to be a representative of how humans see rainbows everywhere. In fact, a rainbow spans a continuous spectrum of colors (no bands).
If there are rainbow bands in the visible spectrum, then there should be rainbow bands in the rest of the spectrum as well, but we just couldn’t see them directly. A near IR sensitive digital camera and a near infrared pass filter allow the near infrared rainbow to be captured.
A near infrared rainbow lies next to a red band of any rainbow, simply because the near infrared region lies right next to the visible red region of the electromagnetic spectrum.
The visible and near infrared rainbows were captured in the evening of June 18, 2011 at approximately 5:24 PM in Bangkok, Thailand. The rainbow showed up after a quick rain and last for about half an hour
(see time-lapse video : http://www.youtube.com/watch?v=pTz-xVjhHPc).
Camera and filter used :
Camera : FujiFilm IS-1
Near IR Pass Filter : Hoya R72 IR Filter
UV/IR Block Filter : Heliopan Digital UV/Infrared Lichtfilter Slim version
Author: Pitan Singhasaneh, Bangkok, Thailand