Weed vaporizers work by heating up your herbs to the appropriate temperature so that the chemicals inside the plant boil away to a vapor which can be breathed in. This is significantly healthier compared with smoking or injesting the herb as it provides a much larger amount of control over dosage and there are a lot fewer side effects.
Weed vaporizers employ numerous methods of heating the herb including thermal conduction, thermal radiation and convection. Thermal conduction is the most widespread method in which the ingredient is placed on a surface that is heated up by butane or a similar heat source which in turn heats up the herb causing it to release its chemicals in vaporous form. Radiation uses an intense light source to send energy into your weed and is not as common. Convection vaporizers heat the air inside the vaporizers and having the air heat the herb.
As different substances have different natural vaporization temperatures it is crucial for a weed vaporizer to be able to control the temperature. As an example, cannabis has a vaporization temperature of 177°C whereas tobacco has a vaporization temperature of 140°C. Being able to precisely set the most suitable temperature means that you get the most chemicals out of your herbs.
Some weed vaporizers come with electronic displays that show both the actual and pre-programmed temperatures so that you can set it specifically as you want it. It is a matter of personal preference but for marijuana it must be over 140°C which is the temperature that trace amounts of THC can be found but under 200°C as toxins start formulating at this high temperature. Most vaporizer users usually choose temperatures around 185°C because this is well below the toxin limit but high enough so that suitable levels of THC and vapor make their way into the collection/inhalation device.
One thing to understand is the density of the vapor makes no difference to the effect that breathing in the vapor has on you. Less dense vapor that you would get with lower temperatures can contain just as much THC as the thicker vapor you get by using higher temperatures.