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seth christian

understand foot candle science

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There's a lot of young film-makers out here that are thinking

that hey...."1000watts should be a 1000watts, regardless if its

a halogen, HMI, flourescent, etc....right!?"

 

I think its good to have a thread on knowing what to expect

if a beginning crew buys a 1000w yellow light from

home depot is going to be slightly different from getting 1000w

HMI that throw a ton more foot candles because of the amps behind it.

 

I think PHOTOS would be great for examples!

 

And stories of what ended up not being enough light, huh! darn,

we'd better run to Walmart and buy some more lights...scenario!

 

so first question:

how many foot candles does a 1000w halagen from HomeDepot give?

and, how many foot candles does a 1000w HMI give?

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Seth,

I would go to the Mole-Richardson web site and look up the performance data for some of their products.

Compare a 1200w fresnel at 20 feet is 160 fc and beam diameter of 14 feet.

Compare a 1000w nook at 20 feet is 40 fc and light spread 26 x 14 feet.

 

Their data gives a very rough idea of what to expect in the real world. good luck

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1000 watts is 1000 watts. But it's a measure of the energy consumed, not the light energy that is produced. The domestic tungsten lamp gives you more heat than anything: an HMI is more efficient, rather than drawing more current.

 

"The amps behind it" won't tell you anything more. It's a matter of the luminous efficiency of the type of light source that will tell you how much light you get on your subject. (Together with issues of whether the light is focussed or radiated in all directions, which affects the intensity of the light rather than the total light output).

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the Mole-Richardson site does have really good spec sheets on comparing kinds of lights and their powers accordingly. Good REFERENCE!

 

it might be pretty useful for someone out there to start a site thats just for this purpose...and actually test every common light and give a yah or nay on contexts to use it in and foot candles thereof, etc...

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Set Lighting Technicians Handbook by Harry C. Box has a table of lamp outputs in it as well as other totally useful data. Many here live out of it just as I do. The most efficient thrower of footcandles per watt is the PAR lamp.

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There's a lot of young film-makers out here that are thinking

that hey...."1000watts should be a 1000watts, regardless if its

a halogen, HMI, flourescent, etc....right!?"

 

I think its good to have a thread on knowing what to expect

if a beginning crew buys a 1000w yellow light from

home depot is going to be slightly different from getting 1000w

HMI that throw a ton more foot candles because of the amps behind it.

 

I think PHOTOS would be great for examples!

 

And stories of what ended up not being enough light, huh! darn,

we'd better run to Walmart and buy some more lights...scenario!

 

so first question:

how many foot candles does a 1000w halagen from HomeDepot give?

and, how many foot candles does a 1000w HMI give?

 

There's so much more to the light than the wattage. In this era of emerging technology wattage is becoming less and less relevant. Consider the emergence of fluorescent and LED lighting. Wattage really isnt the best measure of how much light each will provide. Other factors like the lamps housing and/or lens also greatly affects how a light performs.

 

The conventions in early to mid 20th century lighting were based off the dominance of mole-richardson light fixtures. The assumptions based on the effects of reflectors, fresnel light loss, etc allowed the artist/technican to better predict the effects of 1000w, 5k, etc.

 

Now more than ever the PHOTOMETRICS of a bulb and/or fixture is important to understand. The photometrics of almost evbery fixture is available from the manufacturer. This will help you to understand all aspects of a lighting fixture.

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http://www.lowel.com/dp/dp_b.html#info

 

here's a link to a lowel photometric chart for a dp light.

 

http://www.replacementlightbulbs.com/lampbtl.html

 

here's a link to photmetric data for a bulb.

 

http://www.stlltd.com/rentals/photometrics/s4_photo.htm

 

here's a link for ETC Source Four Leko photometrics. Note how much a difference the lens has on the light output.

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yeah of course joung ones need to know how to desing their light.

 

I use for example.

 

E=25fe2/S(T)

 

25 are the frames...

 

f= t stops or f stops....

s = iso

t= 1/50 if its video...

 

for films...

 

E= 1250fe2/s

 

1250 ... try imagine what does that means....

 

f = stops on the lens...

 

s = iso....

 

for example... if you have a tungsten arri 650 w... (we know 650 is the consumption) not how may foot candles per square meter does it delivers... but as I know it delivers round 52800 fc

 

LETS know how may foot candles do we need for a ISO/ASA 100 at 1/50 at 2.0

 

using the first equation...

 

E= 25(4.0)/2 = 100/2 = 50 FC we need to expose that iso with that speed and that t-stops...

 

so now that we know that... what else do we need?

 

lets put the 650w from arri...

 

to know how much distance do you need the 650 to deliver 50fc we use the next equation...

 

I= E/De2

 

I= 52800/32 = 52800/1024 = 51 fc...

 

so you need to put that 650 at a distance of 32 feet ...

 

use the data sheet of the light companies...

 

or use this... http://calc.arri.de/calculator

 

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