can someone explain how this works, i was under the impresion that i could stick my thermometre where my plants are about 5'' below my lights, but apparently not because it will mess up the reading??? read something about needing a digital thermometre to read it properly....will it be colder than my reading says and is radiant heat bad for the plant?

bump........

put the thermometer in between the plants(shade from the light)and measure.
you want 74 day and 68 night.
this is measuring radiant temp.
Room temperature - Wikipedia, the free encyclopedia
this is ambient.

Infrared Thermometer - Infrared Thermometer made by Mannix - Dickson Supply's AccentShopping.Com 1-800-456-5267 if your talking about this kind of digital thermometer, it will tell you the surface temps of your plants or walls, etc. a regular thermometer will give you ambient or room temp that is for the entire area.

yes true but it depends on where you place the regular thermometer.

how come you don't take the reading directly in the light, surely this is what the plants are getting up the top?

because you are going to get a sky high reading because of the RADIANT TEMP coming directly from the lamp beaming onto the thermo.if you have a basic thermometer just cover the sensor at the bottom with a piece of cardboard(shield it from the direct light) and you will get the radiant temp in between the plants and not from the light source beaming straight on to it.

cool i'm kind of getting it now, so if i want to know how close i can have my light it would be the reading in the shade, does the radiant heat that the top of the plant is getting not damage it though, or do you need to just use a bit of common sense and choose a height where the temp is good and it doesn't feel too hot at the top. reason i'm so bothered about this is i have a cool tube so i'm try to get it as close as possible

Ever notice that you are warmer when the sun is shining directly on you? and it feels cooler in the shade? thats radiant heat from the sun doing that.

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It is far easier to ignorantly control others than it is to wisely control yourself.

that's a perfect example.well explained.