Hi
@Angus
Kelvin is a measure of the colour temperature* of the lighting. And this, in turn is related to the spectrum of the lighting. We see the spectrum of white light every time we look at a rainbow.
Richard
Of
York
Gave
Battle
In
Vain - Red, Orange, Yellow, Green, Blue, Indigo, Violet. The response of the human eye is at its most sensitive with yellow light. However, the plant's 'eyes' see things differently. And this is where it gets tricky. 1 Lux = 1 Lumen per square meter. Lumens are for humans. You probably know all that. PAR is
photosynthetically
active
radiation. A PAR meter ideally 'sees' all colours across the spectrum equally. Each colour corresponds to a wavelength of light - from 400 nanometres (violet) to 700 nanometres (red). As a result of recent research, the upper wavelength limit is now under review.
So, where does this leave us? Unless we know what the spectrum of light looks like, it is not possible to measure PAR. But, approximations can be made. I believe that
@oreo57 uses a decent tool for this purpose. For myself, I'm possibly going to purchase an Apogee SQ-520 PAR sensor.
* an explanation of this means talking about black-body radiation. It gets pretty heavy so that's for another day!
I don't know if any of the above is useful to you. But, it's late in the evening - so that's my excuse!
JPC
