coreywebster
Well-Known Member
I'm posting this info because several times a week a noob panics about grow room temps and very often its due to improper placing of the thermometer.
As indoor growers we all know the importance of proper temps in the grow room, the main temp we want to take is the Air temperature. It used to be stated that optimum temps were between 78-82 degrees F. But I see a lot of folks going much lower than this these days. I'm not going to get into why or even what is the optimum temp. You can make that informed decision yourselves. This is mainly about MEASURING AIR TEMPS CORRECTLY. Because in not doing so you may panic for no reason, go out and buy new fans or spend a grand on an LED when you didn't need to or post 45 threads about the same subject on here. The info below is taken from another site, unfortunately I cannot credit the author as he/she is unknown.
There are two aspects to the thermal environment that you need to be aware of:
1. The AIR temperature
2. The RADIANT temperature
1. Air temperature
Your standard mercury/alcohol-bulb or digital thermometer is designed to measure the temperature of the air (But not radiant heat). This is what is being referred to in the usual growers 'rules of thumb' such as maintaining your grow above 16degC and below 28degC.
Most thermometers are only designed to measure air temperature – growers often mistakenly place their thermometer in direct light; radiant energy will warm your thermometer and give a higher than actual reading.
*Assuming your air is well mixed up by oscillating fans, it doesn’t really matter where you locate your thermometer. The best spot is probably about half the way up a wall, with a piece of cardboard over it (To shade it from radiant heat), exposed to the mixed air in the grow room. Or just above the light line.
2. Radiant temperature
Radiant temperature is the result of heat transfer between objects at different temperatures without what's in-between i.e. the air, being effected. In our case the plants are naturally at a lower temperature that the light and reflector so heat is transferred to the plants foliage from the light/reflector through radiation. This causes the leaves to heat up. The plants can withstand much higher radiant temperatures (around 40-50degC) than they can air temperatures but if this is too high the plants can 'burn'.
'The hand test': Place your hand in a comfortable position for some time at the tips of your plants should be. If your hand feels “hot”, then the lights are too close, the radiant energy is too intense, and light burn may result. Do this test and raise your HID lights/reflectors periodically to keep light burn to a minimum.
So if you have been taking readings directly under your grow light and hitting 90degrees f then hopefully you can now see the problem may not be a problem at all. Reposition that thermometer above your light line and shade it with a piece of preferably white card.
Hopefully this saves some of you flipping out, abandoning your grows or spending money you didn't need to only to find your money was wasted.
As indoor growers we all know the importance of proper temps in the grow room, the main temp we want to take is the Air temperature. It used to be stated that optimum temps were between 78-82 degrees F. But I see a lot of folks going much lower than this these days. I'm not going to get into why or even what is the optimum temp. You can make that informed decision yourselves. This is mainly about MEASURING AIR TEMPS CORRECTLY. Because in not doing so you may panic for no reason, go out and buy new fans or spend a grand on an LED when you didn't need to or post 45 threads about the same subject on here. The info below is taken from another site, unfortunately I cannot credit the author as he/she is unknown.
There are two aspects to the thermal environment that you need to be aware of:
1. The AIR temperature
2. The RADIANT temperature
1. Air temperature
Your standard mercury/alcohol-bulb or digital thermometer is designed to measure the temperature of the air (But not radiant heat). This is what is being referred to in the usual growers 'rules of thumb' such as maintaining your grow above 16degC and below 28degC.
Most thermometers are only designed to measure air temperature – growers often mistakenly place their thermometer in direct light; radiant energy will warm your thermometer and give a higher than actual reading.
*Assuming your air is well mixed up by oscillating fans, it doesn’t really matter where you locate your thermometer. The best spot is probably about half the way up a wall, with a piece of cardboard over it (To shade it from radiant heat), exposed to the mixed air in the grow room. Or just above the light line.
2. Radiant temperature
Radiant temperature is the result of heat transfer between objects at different temperatures without what's in-between i.e. the air, being effected. In our case the plants are naturally at a lower temperature that the light and reflector so heat is transferred to the plants foliage from the light/reflector through radiation. This causes the leaves to heat up. The plants can withstand much higher radiant temperatures (around 40-50degC) than they can air temperatures but if this is too high the plants can 'burn'.
'The hand test': Place your hand in a comfortable position for some time at the tips of your plants should be. If your hand feels “hot”, then the lights are too close, the radiant energy is too intense, and light burn may result. Do this test and raise your HID lights/reflectors periodically to keep light burn to a minimum.
So if you have been taking readings directly under your grow light and hitting 90degrees f then hopefully you can now see the problem may not be a problem at all. Reposition that thermometer above your light line and shade it with a piece of preferably white card.
Hopefully this saves some of you flipping out, abandoning your grows or spending money you didn't need to only to find your money was wasted.