Light sources can be characterized according to their wavelength spectrum as either narrow- or broad-banded. For example, atomic resonance lamps, such as sodium or mercury, emit light only at certain wavelengths.
The spectral bandwidth of light at each atomic line is generally very narrow. Lasers are effectively monochromatic (single wavelength), while arc lamps, such as xenon, carbon arc, and incandescent lamps, emit over a very broad wavelength range with few spectral features.
One useful measurement of light sources is luminous intensity or candela (CD = LM/SR).
Candela is the foundation unit for the measurement of visible light. It is the luminous intensity in a given direction of a source that emits light that has a wavelength of approximately 555 nm (yellowish-green) and a radiant intensity in that direction of 1/683 Watt per steradian.
The candela value is independent of distance. One can think of it as the emission from a lamp without any interest in what happens to the photons that it has ejected. Candela is frequently used when dealing with focused light for LEDs, flashlights, or spots.
DTB can provide testing in accordance with many optical specifications, such as ATPD 2352 for transparent armor and ASTM D 1003 for transmittance and haze. A summary of the relevant optical specifications is listed below:
- ASTM F 801 and ASTM D 2156
- Luminous transmittance, per ASTM D 1003; ATPD 2352, Section 4.4.1; PMA202-07001; MIL-DTL-62420; ASTM F 659; and ANSI/SAE Z26.1
- Photopic, scotopic, and night vision goggle response functions
- Standardized light sources A and C
- Haze, per ASTM D 1003; ATPD 2352, Section 4.4.2; PMA202-07001; ASTM F 659; and ANSI/SAE Z26.1
- Taber surface abrasion resistance testing for interior and exterior (threat surface) wear, per: ATPD 2352, Section 4.3.6; ANSI/SAE Z26.1; and ASTM D 1044
- Optical deviation, per ATPD 2352, Section 4.4.3; ASTM F 801; and MIL-DTL-62420
- Optical distortion, per ATPD 2352, Section 4.4.4, and ASTM D 2156
- Prismatic deviation, per PMA202-07001 and ASTM F 659
- Spherical and cylindrical power, per PMA202-07001, ASTM F 659, and MIL-DTL-62420
DTB’s light analyzer (Spectrophotometer) is an integrated system designed to measure luminous transmittance, as well as haze, with respect to both A and C illuminants.
To measure the illuminance/luminance of an object, our Spectrophotometer can be employed to take information from multiple photometric or radiometric detectors across the surface of an object.
DTB’s testing lab is A2LA accredited (Cert. Nos. 0767.01, 0767.02, and 0767.03) and provides the latest in testing equipment and environments. Our experienced personnel can provide the level of professionalism required for reliable results.
- Optical testing – ASTM F 801-96, ASTM F 2156-06, ASTM D 1003-00, ASTM D 1044-08, and ATPD 2352R and ATPD 2352T, Sections 3.4.1, 22.214.171.124, 3.4.2, 3.4.3, 3.4.4, 4.4.1, 126.96.36.199, 4.4.2, 4.4.3, and 4.4.4
- Abrasion – ANSI/SAE Z26.1-1996, Sections 5.17 and 5.18, and ATPD 2352R and ATPD 2352T, Sections 3.3.6 and 4.3.6