Reconsidering What 'Visible' Means
Laser safety standards have called the spectral band between 400 and 700 nm "visible" for Class 2 lasers since the drafting of the first ANSI Standard in the early 1970s. Although it's technically true that these wavelengths are visible, a wider range can be seen by the human eye. In developing the new ANSI Standard Z36.6 the exact definition of the term "visible" is under debate.
Many standardization efforts define visible light as that which elicits a visual response, and clearly this varies from individual to individual. The International Commission on Illumination defined the visible spectrum as 380 to 790 nm. But even this range is questionable because some human eyes can detect UV wavelengths down to 310 nm. Before the definition of visible is solidified, US Army researchers are awaiting results of studies of aversion response, looking particularly at how pupils close in the 400- to 440- and 650- to 700-nm spectral regions under laser light.
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