Hi,
The relationship between lux and kelvin isn't very crystal clear. Lux is a measure of lumens per square meter. Lumens is the measure of intensity at a wavelength of ~550-600 nm (or green).
Kelvin colour is not really related to the lux. Let's suppose that an MH only produces three spikes of light - one at green, blue and yellow. It is fairly common for MH and fluorescents to do this due to the nature of the technology. If the blue spike moves to the violet...the kevlin increases...but the intensity stays roughly the same. The kevlin increases because the averaged wavelength of the light output is shorter -- which means a higher kelvin light. In other words...the light output has shifted to a blue tone. The green spike is what determines the lux intensity and the green spike stayed the same in both cases.
As for why the water is blue. This has to do with many things. This includes the reflection for the sky and blue-green algae in the water. But, RO/DI water is blue too ...this is actually a chemical property. Water is only semi-transparent at visible light wavelenghts. Its semi-transparency gets worse with longer wavelengths. So, long wavelengths get absorbed faster than short wavelengths in water. Hence, the blue light, which have shorter wavelengths, go through the water deeper than red lights. A similar argument can be made for why the sky is blue.
Hope that helps.
- Victor.
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