*Need filtering for color photography.

*Need filtering for color photography.

use of this figure reveals the envelope's configuration by simply knowing that the code letters associated with the lamp designation are the dimensional descriptive data.

The following examples are offered to clarify this descriptive process:

a.) R40 — This is a reflector flood ("R" type envelope), which is 4%ths of an inch in diameter.

b.) PAR 64 — The designation "PAR" refers to the sealed beam lamp type (Parabolic Aluminized Reflector) which is M/sths of an inch in diameter.

c.) Q1000 PAR 64 — This is the envelope as in (b.), but the "Q" designates a tungsten halogen lamp of 1000 watts inside. ("Q" is a hangover from the early days of tungsten halogen when these lamps were referred to as Quartz Iodine.)

d) Q1000T3 — A tungsten halogen lamp, 1,000 watts, with a tubular envelope 3/sths of an inch in diameter.

Another important element in the construction of lamps is the basing. Figure 2 shows the most common base arrangements used on incandescent-type lamps (also applicable to certain discharge types). This figure can be helpful in establishing whether a particular lamp can be mated to a given fixture.

Figure 1. Lamp envelope configurations.

Color Temperature

Color temperature describes the actual temperature of a "black body radiator" and thereby completely defines the spectral energy distribution (SED) of the object. When the object becomes luminous and radiates energy in the visible portion of the spectrum, it is said to be incandescent. Simply stated, this means that when an object is heated to an appropriate temperature, some of its radiated energy is visible.

The color temperature is usually described in terms of degrees Kelvin. This simply refers to a temperature scale, like Fahrenheit or Centigrade (Celsius). It is in fact the absolute Centigrade (Celsius) scale, which is the temperature in degrees Centigrade (Celsius) plus 273 degrees.

When metal is gradually heated, the first visible color is "dull cherry red." As the temperature is raised, it visually becomes "Orange," then "Yellow," and finally "White" hot. The actual effect of increasing color temperature on the spectral energy distribution is best seen in Figure 3.

Strictly speaking, tungsten filaments are not true black bodies. However, from a practical standpoint, both standard incandescent lamps and tungsten halogen types can be so considered.

Figure 1. Lamp envelope configurations.

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