Article by David Dwyer
There are two main considerations for studio lighting: 1. Lighting of the subject (model or still-life setup) and 2. lighting of the artist's easel and artwork in progress.
First, a few basics on light sources. In an ideal world, it would be wonderful to have constant daylight on both subject and easel, but this is often not possible. Therefore, electrical lights are used in most studio situations, either as the sole light source or for augmenting natural light. In addition to the rating of a light bulb by its power (usually referred to as wattage), two additional descriptive ratings are also used: Kelvin rating and CRI.
The Kelvin rating describes the color temperature of a light source, also known as Color Correlated Temperature (CCT). Candle flame has an 1800 Kelvin rating, incandescent bulbs are in the 2900 K range, and daylight ranges from 5500K (noontime sun) to 7500K (cool Northern latitude daylight). Lower Kelvin ratings are associated with "warmer" light, and higher Kelvin ratings are associated with "cooler" light.
The other numerical rating of a light source is the Color Rendering Index (CRI) which is a measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. The perfect CRI is 100.
Typically, a bulb is classified as "full spectrum" when it has a CRI above 90 and a Kelvin temperature rating around 5500 K, although manufacturers are liberal in their use of the “full spectrum” label – buyer beware!
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The type of lighting used to illuminate the subject (whether it be a figure model or a still life setup) is the choice of the artist. Traditionally, artists have sought out studios with natural light originating from north-facing skylights, which provide relatively cool natural light that remains fairly constant throughout daylight hours. To reproduce this type of lighting with electrical lights, bulbs with a Kevin rating of at least 5500 are necessary. If a warmer-quality light is desired on the subject, then a lower Kelvin-rated bulb can be used.
Lighting on the easel must also be considered carefully. A painting completed with a warm, incandescent light directed onto the easel will often look pallid and cool when viewed later in natural daylight or under fluorescent lights. For that reason, a full-spectrum bulb is recommended if the artist cannot have the easel lit by natural light alone. It is also highly recommended that no matter how the easel is lit, the artist should periodically take the artwork-in-progress into a natural light environment to judge the warm-cool balance of the painting (as well as the overall value range of the artwork).
The second consideration in easel lighting is avoidance of having a bright light shining on the top portion of the drawing or painting, while the lower portion of the artwork remains less well lit. This uneven lighting results in a completed work in which the top half of the drawing or painting looks relatively too dark when the completed work is viewed later in diffuse, even lighting. The solution is to use a lower wattage bulb in one's easel light, and to also cover the light with a piece of diffusing paper (which is possible when using a daylight fluorescent bulb but not possible when using an incandescent bulb because of fire hazard of the hot light bulb -- see below.)
Within the last few years, many "daylight fluorescent" lights have become commercially available, resulting in excellent choices for both subject lighting and easel lighting. (These daylight fluorescent bulbs are a huge improvement over the older "daylight" incandescent bulbs, many of which were simply ordinary incandescent bulbs coated with a tinted covering, skewing the light emitted towards a pinkish or bluish spectrum.) Many of these newer compact daylight fluorescent bulbs are engineered to screw into a standard light bulb socket. Although the initial cost of each bulb is higher than for most incandescent bulbs, e.g. $10/bulb vs. $1/bulb, daylight fluorescent bulbs have a very long lifespan (10,000 hours or more) as compared to the shorter life of an incandescent bulb (often 1000 hours or less). Additionally, daylight fluorescent bulbs operate at cooler temperatures than incandescent bulbs, making it possible to position diffusion screens or gels in front of the bulb to adjust not only the temperature of the light beam but also avoid harsh lighting.
The best daylight fluorescent lights which I've found are available on the web from Full Spectrum Solutions. These bulbs are called Blue Max compact fluorescent lights; they have a CRI of 93+ and a Kelvin rating of 5500 K. They have a standard screw-type base and are available in 9W, 13W, 18W and 23W – equivalent to 40W, 60W, 75W and 100W incandescent bulbs. The 9W bulb is ideal for easel lighting, especially if a sheet of diffuser paper is used in front of the bulb (this white translucent paper is available at Glazer Camera Supply in Seattle). Higher-wattage Blue Max bulbs can be used for lighting casts or still-life set-ups; I often use black-coated foil (also available at Glazer’s Camera Supply) to create a coned-down light tunnel in front of the goose-neck lamp lighting my still-life setup in order to create a narrow beam of light upon the objects that I am painting.
As an acceptable alternative bulb for still-life setup lighting, I've used a compact daylight fluorescent "spot" available from Pacific Lamp and Supply (5935 4th Avenue South) here in Seattle. This bulb is manufactured by TCP (#PF310650K – Flat par 30 daylight fluorescent spot 16W) and is equivalent in power to a 75W incandescent bulb. It has a 5000K rating (as compared to 5500K for Blue Max) and a lower CRI than the Blue Max bulbs (82 CRI for the TCP bulb). Nonetheless, I’ve found it to be quite satisfactory.
An alternative for an easel light is the clip-on 13W light from OTT-Lite. Finding the technical specs on the 13W elongated tubular "TrueColor" bulb used in this light is difficult. It appears that this bulb has a Kelvin rating of around 5000 - 5600K. Some sources indicate that the CRI rating of the bulb is as low as 82 to 85. One disadvantage of this clip-on light is that the flexible gooseneck portion of the fixture is quite short, limiting the adjustability of the light’s position with respect to the artwork on the easel. Given the relatively high cost of this clip-on light ($50 or more, fixture and bulb included), I believe that the Blue Max bulbs used in standard easel gooseneck light fixtures are probably preferable for easel lighting. (If you’re still interested in the OTT-light, Dick Blick’s prices appear to be very competitive, although shopping around on line is worthwhile.)
If possible, it is optimal to have at least some natural daylight shining on both the subject and the easel even when daylight fluorescent bulbs are used. No matter how high the CRI-rating of a light bulb, even a small amount of natural light is effective in "filling out" the spectrum of light illuminating the subject as well as the artwork being produced. I've found that paintings produced under these conditions have the most satisfying warm-cool balance at completion.
