Humidity Riddle

So. I have two lights in my flower room, a 600 under a parabolic reflector, and a new Timber 4vs (second on order). I have identical thermometer/hygrometers with probes at canopy level for both, as well as a different brand for room temp/humidity. All three read differently. Of course I can understand the temp differences, but I don't understand why the humidity numbers are different. Yesterday: 54% humidity under the 4vs, 66% under the parabolic, which I can somewhat understand, as it's shape could hold both temp and humidity under it, and 76% on the room thermo/hygro. I'm imagining there is some science behind this that I don't understand. If anyone has some insight, please share! Thanks everyone...

I'm interested too

the humidity number is probably giving you relative humidity
it's a measure of how much water vapor the air can hold based on temperature
and that calculation changes with the temperature

Higher temp air will hold more water vapor, for every 18 degrees of temp increase the amount of water vapor capacity before it hits 100% is doubled. 68 degrees holds twice as much as 50.

Thats why it’s advised to regulate temps in order to avoid humidity related issues.

Different brand hygrometers might show slightly different readings, I have four (same make/model) within one inch of each other, two have same number, the other two are a percentage high and two points lower.

Height of meter will influence reading as well if not the same

Higher air temp holding more humidity makes sense, and would definitely explain the difference between the two lights. The hps canopy is 8-10 degrees warmer than the LED canopy. The room hygrometer is the different brand, and i have a suspicion it reads higher than it should. Canopy temp under the 600 is roughly 80, while humidity is showing roughly 62. Room air temp is 74, but humidity is showing mid 70's, much higher than i think it should be. I should put one of the probes in its place and see what it reads. There are height differences between the three, but I'd say they're all within 18" of one another. Thank you for the insight!

igrowone said:

the humidity number is probably giving you relative humidity
it's a measure of how much water vapor the air can hold based on temperature
and that calculation changes with the temperature

Click to expand...

exactly. The temps are different, so the air has a different capacity. PLUS, they are tools that are not really calibrated.