The term brightness should be used only for non-quantitative references, e.g. in the context of physiological sensations; that is recommended by the U.S. Federal Standard 1037C, for example. Nevertheless, the term is frequently used in the context of lasers and laser beams (see below), but often with a purely descriptive, non-quantitative meaning, i.e., without specifying actual quantitative values with certain units. For actual quantitative references, one should actually used the term radiance, which is the total power divided by the product of the mode area in the focus and the solid angle in the far-field; the units are then usually W cm−2 sr−1.
In other case, brightness is sometimes used instead of the photometric quantity luminance. The important difference is that radiometry deals with optical powers and related quantities, whereas photometry estimates the intensity of optical radiation as perceived by the eyes.
Brightness in Laser Technology
In laser technology, the term brightness is often said to be higher for one type of laser than for another, for example, but rarely with an actual quantitative specification (some numbers and units). What is usually meant is the clearly defined term radiance. That implies e.g. that the brightness of a laser is used if its beam quality is reduced for a fixed power level.
The term also occurs as part of composite terms:
- Brightness converters are essentially devices which receive optical radiation and emit radiation with a higher radiance. That is not possible with passive optical elements, but e.g. with certain optically pumped lasers.
- High brightness laser diodes is an alternative term for broad area laser diodes, indicating that those have a higher radiance than diode bars, for example.
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