Be careful with your new par sensors, they arent the most sturdy things. Also be aware that there is a lot more than first impression: how do tthey react to more linear or more diffuse light (some will give low readings if the light source is close and with light coming from all kind of angles rather than straight, if sensor is angled or no).
- The response curve: how much par they measure depends of nm: uv, violets, and reds, 660 and up, will not show up equally , to the rest of the spectrum. The kind of precision youre talking about is high end Licor sensors like cobkit uses. +1000 dollars for the sensor, then you need the actual reader.
Another issue: you put your par sensor under the light and try to hold still, the numbers on the sensor dance up and down quite a lot, like about 50ppfd or more. Thats a lot of variance and makes it hard to draw hard conclusions from the value. I truly think you need to watch the plants more than any meter. I think the values on our meters, temps/rh/par/lux and especially vpd only really indicate in which direction to take your grow. After that its incremental steps towards that direction, looking for praying leaves, with no burnt tips, no deficiencies, tacoing or other weird stuff, fast drinking plants etc.
For the purpose of really getting into nittygritty details id go for datalogging environment, with sensors in cannopy, undercannopy and heck maybe even in the pot, making sure you get something which will spit out vpd values with you not having to do the calculations.
We had a par meter and it served us "well": it was enough to convince my grow bro we can do leds and we started throwing up panels which got a huge ball rolling. But it promptly broke and now we just do a cheap lux meter and push everything until we see signs of unhappy plants.
