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Standard Measurements for the Color Characteristics of Light


1. Color Temperature: expresses the color appearance of the light itself
2. Color Rendering Index: (CRI), a term used to describe the extent to which an artificial light source is able to render the true color of objects as seen by natural outdoor sunlight which has a CRI of 100.

Color Rendering Index

Incandescent is used as the base reference of 100 CRI. Compact fluorescent lamps are usually graded at 82-86 CRI, which is considered high quality color rendering. CRI is a more important consideration for retail lighting design than it is for office lighting. Any CRI rating of 80 or above is considered high and indicates that the source has good color properties. Incandescent lamps and daylight have a CRI of 100, the highest possible CRI. The higher the CRI of the light source, the "truer" it renders color.

Color Temperature

Refers to the way color groups are perceived - the psychological impact of lighting. Color temperature is how cool or warm the light source appears. The color temperature of a light source is a numerical measurement of its color appearance. This temperature is based on the principle that any object will emit light if it is heated to a high enough temperature and that the color of that light will shift in a predictable manner as the temperature is increased. This system is based on the color changes of a black metal as it is heated from a cold black to a white-hot state. As the temperature increases, the color would shift gradually from red to orange to yellow to white and finally to a blue white. Color temperature is measured in degrees Kelvin (K). Colors and light sources from the red/orange/yellow side of the spectrum are described as warm (incandescents) and those toward the blue end are referred to as cool (natural daylight).

The sun for example rises at approximately 1800 Kelvin and changes from red to orange to yellow and to white as it rises to over 5000 Kevin at high noon. It then goes back down the scale as it sets.

The most typical Kelvin degree lamps used in task lighting are as follows:

2700°          Friendly, personal, intimate                  Homes, libraries, restaurants
3000°          Soft, warm pleasing light                      Homes, hotel rooms and lobbies
3500°          Friendly, inviting, non-threatening         Executive offices, public reception areas, supermarkets
4100°          Neat, clean, efficient                            Office, classrooms, mass merchandisers, showrooms
5000°          Bright, alert                                         Graphic industry, hospitals
6500°          Bright, cool                                          Jewelry stores, beauty salons, manufacturing

Color Temperature:

Standard Domestic Light Bulb (40-60w) 2800K
Standard Domestic Light Bulb (100-200w) 2900K
Standard Domestic Light Bulb (500-1000w) 3000K

These bulbs will be significantly "warmer" (orange/red) than tungsten light sources designed for photographic purposes. The color temperature of quartz halogen fixtures for photography  is usually 3200K. 

Standard household bulbs are not very diffuse. They tend to burn hotter in the center. You may find this undesirable, especially, if the light source is in frame.

Enlarger Bulbs are widely used in motion picture lighting. They are evenly diffuse across the surface of the bulb, have a proper color temperature of approximately 3200K and come in three wattages.

        PH211 = 75w (color 3200°K)
        PH212 = 150w (color 3050°K)
        PH213 = 250w (color 3400°K)

Photofloods (standard pear shaped) are another option. The most common sizes are: 250w and 500w.

        BBA (No.1) = 250w (color white 3400°K)
        BCA (B-1) = 250w (color blue 4800°K)
        ECA = 250w (color white 3200°K
        ECT = 500w (color white 3200°K)
        EBV (No.2) = 500w (color white 3400°K)
        EBW (B-2) = 500w (color blue 4800°K)

Photoflood reference chart:

Photoflood 3200° 3400° 4800°
250W ECA, BAH (300W) BBA BCA
500W ECT EBV EBW

Reflecting Globes (RFLs) (mushroom shaped) are another option:

        DAN (R-20) =200w (3400K)
        BEP (R-30) = 300w (3400K)
        EAL (R-40)= 500w (3300K)

 

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