I’m going to try and cover a lot of ground in these posts, I will try to put links to more info in areas where I skim, Wikipedia has some great info! We will start by discussing some of the things that make up suitable light for photography.
What makes good light?
There are several parameters one must look at to determine the quality of a light source, we’re going to spend a little time talking about them here.
Temperature/White Balance
The color temperature of the light, measured in Kelvin Degrees, indicates the spectrum distribution as related to a black-body emission. I will not attempt to cover this fully, but a few common numbers are: Direct Sunlight 5500K, Shade 6500K, Tungsten/Incandescent 3500K, and Strobe/flash 5500K. Fluorescent lamps can have color temperatures as low as 3000K and as high as 8000K, making it difficult to prepare to shoot under fluorescent lamps you haven’t seen before.
CRI Color Rendering Index is a measurement of how well a given light source matches the spectrum distribution of a black body emission. Light that comes from black body sources: daylight, tungsten, and halogen, has a CRI of 100, or a 100% match to the expected black body spectrum distribution. Metal Halide and Sodium Vapor lamps can have CRIs as low as 45, hardly suitable for a work environment, much less photography. Most modern fluorescents will have a CRI of over 70, making them OK, but not great light sources. Fluorescents are however, available with CRIs as high as 98, making them indistinguishable from natural light. A fluorescent with a CRI of at least 90 is suitable for most all photography, giving you full rich colors that jump with vibrancy.
Efficiency You may think efficiency in photographic lights is an after thought, and it is one of the lower priorities, but the thing to remember is that all of that energy wasted to inefficiency is still emitted as heat. Thus, any increase in efficiency is a decrease in the heat produced. Cooler lights equals more comfortable, patient, and less irritable clients, happy clients equals repeat customers equals more money 
Another case for efficiency is that the less power you use the fewer cables you have to drag around during setup, and the lighter and easier to carry your equipment is. So efficiency is important, just for different reasons than maybe you thought.
So the thing to remember, in choosing your continuous light sources, is the closer the temperature to daylight (5500K) and the higher the CRI, the better, some efficiency thrown in doesn’t hurt. Next post we’ll discuss the products available to pro photographers and their associated pros and cons.
See you then,
Andrew Rodgers
http://groups.google.com/group/wave-protocol
Hydrargyrum medium-arc iodide lamp
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Continuous Lighting; The Pro’s best kept secret: Part 1
I’m going to try and cover a lot of ground in these posts, I will try to put links to more info in areas where I skim, Wikipedia has some great info! We will start by discussing some of the things that make up suitable light for photography.
What makes good light?
There are several parameters one must look at to determine the quality of a light source, we’re going to spend a little time talking about them here.
Temperature/White Balance
The color temperature of the light, measured in Kelvin Degrees, indicates the spectrum distribution as related to a black-body emission. I will not attempt to cover this fully, but a few common numbers are: Direct Sunlight 5500K, Shade 6500K, Tungsten/Incandescent 3500K, and Strobe/flash 5500K. Fluorescent lamps can have color temperatures as low as 3000K and as high as 8000K, making it difficult to prepare to shoot under fluorescent lamps you haven’t seen before.
CRI Color Rendering Index is a measurement of how well a given light source matches the spectrum distribution of a black body emission. Light that comes from black body sources: daylight, tungsten, and halogen, has a CRI of 100, or a 100% match to the expected black body spectrum distribution. Metal Halide and Sodium Vapor lamps can have CRIs as low as 45, hardly suitable for a work environment, much less photography. Most modern fluorescents will have a CRI of over 70, making them OK, but not great light sources. Fluorescents are however, available with CRIs as high as 98, making them indistinguishable from natural light. A fluorescent with a CRI of at least 90 is suitable for most all photography, giving you full rich colors that jump with vibrancy.
Efficiency You may think efficiency in photographic lights is an after thought, and it is one of the lower priorities, but the thing to remember is that all of that energy wasted to inefficiency is still emitted as heat. Thus, any increase in efficiency is a decrease in the heat produced. Cooler lights equals more comfortable, patient, and less irritable clients, happy clients equals repeat customers equals more money
Another case for efficiency is that the less power you use the fewer cables you have to drag around during setup, and the lighter and easier to carry your equipment is. So efficiency is important, just for different reasons than maybe you thought.
So the thing to remember, in choosing your continuous light sources, is the closer the temperature to daylight (5500K) and the higher the CRI, the better, some efficiency thrown in doesn’t hurt. Next post we’ll discuss the products available to pro photographers and their associated pros and cons.
See you then,
Andrew Rodgers
Hydrargyrum medium-arc iodide lamp