The best way to gauge a particular exposure is by the use of an external, hand-held photoelectric exposure meter. For many shooters using most cameras, the most reliable results can often be obtained by sticking with the automatic settings and point and shooting. The use of lights For the average filmmaker, a good rule could be never use lights unless absolutely necessary. Tungsten lighting should never be mixed with daylight when shooting color film. Tungsten light, however powerful it may appear, contains a strong element of red.
Daylight contains a strong element of blue.
Color film has to be specially balanced for use with artificial or daylight. If a daylight film is used in artificial light, it will appear ver pink where the tungsten light has been strongest. An artificial light film used in daulight appears correspondingly blue. Filters are available to convert one type of film to another. It is then quite permissible to supplement daylight with articial light.