First of all, as you suspected, both terms relate directly to light. However they are two separate measurements of two separate theories.
Nanometers relate to the wave length of a particular color of light. A light wave travels in a up / down snake like fashion or as a wave on the ocean, hence the reference light wave. To measure a light wave, we draw an imaginary line through the middle of a complete wave and measure the distance from the start to the end. This measurement is very small and is done in nanometers. A nanometer is one billionth of a meter or 10 -9. If we look at a chart of the visual light spectrum, the color red would show up as a light wave that is 700 nanometers or 7 billionths of a meter long. Violet is 400 nanometers long. All other colors in the visible light spectrum are divided at the fifty nanometer increments. Using a simple acronym "ROY G BIV" we are able to remember the visible light spectrum; Red, Orange, Yellow, Green, Blue, Indigo, Violet. Based upon what I said previously, if Violet is 400 nanometers long, Blue would be 500 nanometers.
We use the color of light when concerned with a camera's response to a particular style or type of lighting. For example: If we have a parking lot that is lit by yellow sodium vapor lighting, it is imperative that we use a camera that responds well to the color yellow. By referring to the camera's spectral response chart, we can calculate how much video image a camera will produce under yellow light as opposed to white, red, or green light. Once verified, the only hold on whether or not we could use the camera in the parking would relate to the camera's overall sensitivity. Therefore, if the camera's overall sensitivity (ability to see in lower light) is equivalent or better than the amount of reflected light provided, at night, this would be an excellent choice for our parking lot.
Kelvin on the other hand refers to the overall temperature of the light. This came about when a man named Kelvin discovered that if he heated up an iron bar, each degree of temperature difference would produce a different affect to the spectrum output of the bar. That is, once heated up, the bar produced light. However at 300 degrees Kelvin, the bar produced a very even amount of visible light and an extreme amount of infrared light. At 250 degrees Kelvin, the bar produced a very even amount of visible light with a small amount of infrared and a little ultraviolet. Therefore, this measurement is very important to us when the camera is tested for sensitivity. If a manufacturer uses a lamp with a Kelvin rating of 300 degrees, the sensitivity rating for his camera might be extreme if the camera is sensitive to infrared lighting. This is because the sensitivity ratings for cameras are based upon visible light, not infrared. Therefore, the accepted (but not enforced) industry standard for testing a camera's sensitivity is done using a light with a Kelvin rating of 250 degrees.
At the end of the day, the spectral response of a camera, as measured in nanometers is a field number that will apply under abnormal or unusual visible or infrared lighting conditions. Kelvin ratings can be used in the field to determine the amount of visible and/or infrared light or the actual temperature ratings of lamps as it applies to the spectral response of a camera, but for the most part is not an everyday serious consideration.
At any rate, I sincerely hope that I have not confused the issue for you. Please feel free to fax forward any additional questions or queries that you may have. I am in your service.
