If a reptile temperature gets to low what does it need to do

Reptiles require external heat to thermoregulate.  If a reptile's temperature gets too low, it will need to find a source of heat to raise its body temperature.  In the wild, most reptiles do this by basking in the sun.  In captivity, heat lights, heating pad, and other heat sources are provided to allow them to thermoregulate.

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.