How to put together a Lighting Kit for Video (Part One): Quantity of Light
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This article is written for the absolute novice who wants to put together a basic lighting kit for video work.
A lighting kit (unlike a computer or a camera) is an evolving thing. Accept this, and you’ll be all right.
What you buy today might lay unused tomorrow. You can never have enough lights, and every variable (every video production) alters your perception of what a lighting kit should contain. And of course, the more you shoot, the more you learn – this changes your aesthetic sense of what work for you.
No matter what the lighting scenario, there are some fundamental principles that limit your choices and ‘box’ you into specific options. You cannot circumvent these factors – they are issues imposed on you due to science or technology. You will face these problems even when you have ‘trucks-full’ of the best lights in the world.
Let’s look at how the quantity of light required over a given area determines our choices.
Quantity of light
The quantity of light is governed by three factors:
For any given scenario, no matter what your artistic intention is, you have to base the quantity of light required (in lumens) over the area you want to cover, and according to the intensity of the light source. Look at this simple example:
The sun throws light in all directions (3600), and the orange patch is our ‘party strip’. The area of the orange patch decides how much light it gets, since we can’t control the intensity of the sun (actually we can, but that’s for another day).
Let’s keep things as simple as can be. The sun delivers a total of 100,000 lumens per square meter (lux). If our party patch had an area of 30 x 30 feet (900 sq.ft or about 82 sq.m), then the lumens falling on it is about 8 million.
Why we’ll always need ‘big’ lights
Let’s say we tried to light the same patch with a 100 Watt tungsten bulb with an LPW rating of 10 (if you don’t understand these terms, please read the links I’ve given above – it’ll make your life a lot easier). This gives us 1000 lumens. For simplicity’s sake we’ll assume all of these lumens are available for our patch, and there’s no light loss at all. The lumens per sq.m (or lux) is 1000/82 = 12.2 lux.
So, how many 100W bulbs do we need to replace the sun? About 8,000. That’s 820 KW of light.
How many 18K HMIs (at about 85 LPW) does it take to do the same thing? About five at full spot. Now you know why we need large HMI lights for exterior daylight sets. Here’s the bummer: No matter how good a camera ISO becomes, and no matter how many ND filters you use, if you want to match the sun, you need to match the sun in lumens. Slice it any way you like, with any technology practically available today for filmmaking – big expensive lights are here to stay.
An 18K HMI kit runs about $25,000, excluding grip and transportation. Five of them will cost $125,000. 8,000 $2 100 Watt tungsten bulbs will cost $16,000, plus the cost of rigging them. Don’t forget that 5 HMIs are about 90 KW, while 8,000 incandescent bulbs are about 800 KW. Before you jump up and down thinking 8,000 bulbs are way cheaper, please call a few rental houses and find out how much it costs to rent generators (and trucks, with drivers and grips) to cover 800 kW. After you’ve recovered, continue reading.
Light and Exposure
From everything we’ve covered, here is a simple inaccurate (but good enough for our purposes) table that plots exposure alongside f-number, area and light output (Click to enlarge):
A lot of this has been covered already in the above links, but to summarize, note the following:
How to determine the quantity of light
If you step back and assess your requirements, you will notice that most lighting scenarios can be bracketed into spaces similar to what’s given in the above table. This is why lighting manufacturers stick to traditional wattages. It’s not something they conjured up over the weekend. It’s taken them a hundred years of experience to arrive at these figures.
As a general guideline, you could find the total quantity of light in the following way:
Slowly but surely, you’ll arrive at a set of lighting ‘classes’ for your scenes. Try it, it’s not that hard. Then, it’s only a matter of finding out if you have the budget to match your requirements.
But hold on, we’re not done yet.
The next step is determining the kinds of light you’ll be using. That’s what we’ll cover in Part Two.
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April 1, 2013