What is Lux and footcandles ?.Help please

[Jassim]

Im using a sekonic L-358 lightmeter for videos which gives me reading in Full,1/2/ or 1/3 stops.It wasn't until today i found out that there is a chart in the users manual to convert the EV Value to Either Lux or Foot candles .Please tell me what do they do and when do we use it .Thanks

 

[Razz16mm]

Footcandles and Lux are the standard references for illumination based on a defined light source called the candela. Foot candle = the illumination of one square foot by one candela at a distance of one foot. Lux = Illumination of one square meter by one candela at a distance of one meter. These are the base units of measurement of light itself in physics.

 

[j1clark@ucsd.edu]

The basic cinematography formula for exposure is:

100 footcandles @ 1/48 (180 deg. shutter for 24 fps.) @ ISO 100 @ f/2.8

So, when measuring incident light, one needs this exposure to yield a 18% grey card a 'middle grey' tone. As most rules of thumb, there can be some amount of variation with one's camera, meter, and in the olden days film type.

But that's the basic exposure formula.

Since you indicate you are in India, where the metric system is used, one would use lux(lx), the converstion for footcandles(fc) -> lux(lx) is:

1 footcandle = 10.76391 lux,

or the above forumula:

1076.391 lx @ 1/48 @ ISO 100 @ f/2.8

----

Most 'pro' lights have photometric data given in footcandles/lux. Therefore when setting up lights one can look on a table and find footcandles/lux at specified distances of the subject to the light.

This allows one to specify how much lighting equipment one needs ot setup lighting ratios and verify the illumination of a scene before one gets to the set.

The meter use 'on set' is used to verify and tune the lighting for the desired look.

 

[Jassim]

Thanks for making it less confusing

Thanks for making it less confusing

The basic cinematography formula for exposure is:

100 footcandles @ 1/48 (180 deg. shutter for 24 fps.) @ ISO 100 @ f/2.8

So, when measuring incident light, one needs this exposure to yield a 18% grey card a 'middle grey' tone. As most rules of thumb, there can be some amount of variation with one's camera, meter, and in the olden days film type.

But that's the basic exposure formula.

Since you indicate you are in India, where the metric system is used, one would use lux(lx), the converstion for footcandles(fc) -> lux(lx) is:

1 footcandle = 10.76391 lux,

or the above forumula:

1076.391 lx @ 1/48 @ ISO 100 @ f/2.8

----

Most 'pro' lights have photometric data given in footcandles/lux. Therefore when setting up lights one can look on a table and find footcandles/lux at specified distances of the subject to the light.

This allows one to specify how much lighting equipment one needs ot setup lighting ratios and verify the illumination of a scene before one gets to the set.

The meter use 'on set' is used to verify and tune the lighting for the desired look.

Thanks for making it less confusing ,im not much of a maths guy .Now i know why they are calculated :thumbsup: