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Photonics Dictionary

absolute luminance threshold

The absolute luminance threshold is the lowest luminance level of a light source or illuminated object that can be detected by the human eye under specific conditions. This threshold represents the point at which a stimulus becomes just barely visible against a completely dark background.

Luminance level: It quantifies the smallest amount of light (measured in units such as candelas per square meter, cd/m²) that can be detected by the average human eye.

Measurement conditions:
The absolute luminance threshold is typically measured under controlled conditions in a dark environment to eliminate any background light that might interfere with detection.

Influencing factors:

Adaptation state:
The threshold can vary depending on whether the eyes are adapted to darkness (dark-adapted) or to light (light-adapted).

Age and health:
The sensitivity of the visual system can be affected by age, eye health, and individual differences.

Wavelength:
The threshold can vary with the wavelength of the light; the human eye is more sensitive to certain wavelengths (e.g., green light) than others (e.g., red or blue light).

Understanding the absolute luminance threshold is important in various fields such as:

Lighting design:
Ensuring adequate illumination in environments to meet visibility requirements.

Safety and signage:
Designing signs and signals that are visible under low-light conditions.

Vision research:
Studying the limits of human visual perception and diagnosing vision impairments.

In a dark room experiment, a small light source gradually increases in brightness. The absolute luminance threshold is reached at the point when a participant first reports seeing the light. For example, this might be at a luminance level of 0.001 cd/m² for a dark-adapted eye.
 
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