Walter_Graff
Carbonite Member
I've noticed a bit of an error by some in regards to how light and specifically lighting instruments work. Some believe that a 2k fixture for instance is twice as bright as a 1k fixture. This is an error in thought.
In the purest sense any light source just like sound gravity and a few other applications all fall under a mathematical law. Take any single bare source of light and the law states that the energy given off at twice the distance is only 1/4 the intensity. The reason is because each time you move 1 times the radius light is spread four times the area and hence is 1/4 quarter the intensity. This is a universal law called the inverse square law and it applies any single source of light. Add a reflector and a filament and it becomes much more difficult to compare two light sources.
Take for instance two ARRI open face fixtures. At 9 feet a fully flooded 1000 watt fixture makes 110 fcs of light. So how much light do you think a 600 watt fixture at full flood gives off at 9 feet? 70 or 80 foot-candles given the difference in wattage?
Well wouldn't you know, it gives off 104fcs, nearly the same. Only a 6 foot-candle difference.
What about twice the light of the 1000 watt fixture? At 9 feet a 1k Arri at full flood gives off 110 foot-candles as I said. Twice the light as in a 2k should be 220fcs, no?
But an Arri 2k at full flood at 9 feet makes 304 fcs of light or nearly three times as much light. Why the discrepency?
Part of it has to do with the reflector. At wide open each reflector creates a slightly different beam angle. Secondly the filiment.
The point is that one can not say that a 2000 watt fixture makes four times the light as a 500 watt fixture. If it was a bare lamp and all things being equal you could apply the inverse square law easily, but add a reflector and while the inverse square law applies to each fixture individually, as you can see comparisons are not so simple.
Or put it this way, spot both the 600 watt fixture fully and the 1000 watt fixture fully and you end up with a 1.1 meter beam of light from each. But the 1000 watt fixture produces 1345 fcs while the 600 watt fixture makes only 509. The inverse square law is correct based on each fixture by itself and a point of light, but once again the difference between the two is substantial.
And to add to the comparison, how about a Lowel 1000watt DP light at full flood vs a Lowel 500 watt omni light at full flood. Maybe at least or near to twice the intensity, no?
No! at five feet a 500 watt light makes 250 foot candles and a DP twice the wattage makes 297. So for twice the wattage you get only 47 foot-candles more light. What is it a lot of guys say, it's not size but how you use it? well in lighting it isn't always about size.
At 10 feet its 88 fcs for the 500 watt fixture and a very close 88fcs for the 1k.
At 15 feet its 40 vs 35 and then at 20 feet its 23 vs 20.
The point is one can not simply say they need four times the light if they are using a gel that cuts a light four times the intensity. It all depends on the instrument they are using.
In the purest sense any light source just like sound gravity and a few other applications all fall under a mathematical law. Take any single bare source of light and the law states that the energy given off at twice the distance is only 1/4 the intensity. The reason is because each time you move 1 times the radius light is spread four times the area and hence is 1/4 quarter the intensity. This is a universal law called the inverse square law and it applies any single source of light. Add a reflector and a filament and it becomes much more difficult to compare two light sources.
Take for instance two ARRI open face fixtures. At 9 feet a fully flooded 1000 watt fixture makes 110 fcs of light. So how much light do you think a 600 watt fixture at full flood gives off at 9 feet? 70 or 80 foot-candles given the difference in wattage?
Well wouldn't you know, it gives off 104fcs, nearly the same. Only a 6 foot-candle difference.
What about twice the light of the 1000 watt fixture? At 9 feet a 1k Arri at full flood gives off 110 foot-candles as I said. Twice the light as in a 2k should be 220fcs, no?
But an Arri 2k at full flood at 9 feet makes 304 fcs of light or nearly three times as much light. Why the discrepency?
Part of it has to do with the reflector. At wide open each reflector creates a slightly different beam angle. Secondly the filiment.
The point is that one can not say that a 2000 watt fixture makes four times the light as a 500 watt fixture. If it was a bare lamp and all things being equal you could apply the inverse square law easily, but add a reflector and while the inverse square law applies to each fixture individually, as you can see comparisons are not so simple.
Or put it this way, spot both the 600 watt fixture fully and the 1000 watt fixture fully and you end up with a 1.1 meter beam of light from each. But the 1000 watt fixture produces 1345 fcs while the 600 watt fixture makes only 509. The inverse square law is correct based on each fixture by itself and a point of light, but once again the difference between the two is substantial.
And to add to the comparison, how about a Lowel 1000watt DP light at full flood vs a Lowel 500 watt omni light at full flood. Maybe at least or near to twice the intensity, no?
No! at five feet a 500 watt light makes 250 foot candles and a DP twice the wattage makes 297. So for twice the wattage you get only 47 foot-candles more light. What is it a lot of guys say, it's not size but how you use it? well in lighting it isn't always about size.
At 10 feet its 88 fcs for the 500 watt fixture and a very close 88fcs for the 1k.
At 15 feet its 40 vs 35 and then at 20 feet its 23 vs 20.
The point is one can not simply say they need four times the light if they are using a gel that cuts a light four times the intensity. It all depends on the instrument they are using.
