Bilingual edition: English is preserved and Chinese follows each unit. Terminology uses the confirmed v20260916 glossary; automated semantic review remains traceable.
中英双语版：英文原文完整保留，中文紧随对应单元；术语采用 v20260916 确认表，自动语义审校结果可追溯。

Luminous Power Per Unit Area of Surface
(Illuminance)

单位面积表面的发光功率（光照度）

The power per unit area on an illuminated surface, sometimes called areance, is distinguished from the similar quantity for the source. In radiometry the surface areance may be called irradiance and luminous areance may be called illuminance. This is the quantity of practical importance in judging whether an area is lighted well enough for reading or other activities. The illuminance is measured in lux, but the older unit footcandle is still encountered.

单位面积上的照度，有时也称为光通量密度，应与光源的类似量区分开来。在辐射计量学中，表面光通量密度可能称为辐照度，而光通量密度可能称为照度。这是判断某一区域是否足够明亮以用于阅读或其他活动的重要量。照度的单位是勒克斯，但较旧的单位英尺烛仍然会被遇到。

Examples of common illuminance levels from Wikipedia at right.

来自维基百科的常见光照度水平示例。
Illuminance Ev = Luminous intensity Iv /radius2

A source with luminous intensity Iv = candela

一个发光强度为 I_v 的光源，单位为坎德拉
中文译文中的待填/计算数值依次对应：1：iv。实际数值以上方原输入框为准。

at a perpendicular distance of r = m = ft

在垂直距离为 r = m = ft 的地方
中文译文中的待填/计算数值依次对应：1：r 2：rc。实际数值以上方原输入框为准。

provides an illuminance of Ev = lux = footcandles.

提供光照度为 E v = 勒克斯 = 英尺烛。
中文译文中的待填/计算数值依次对应：1：ev 2：evc。实际数值以上方原输入框为准。
Include surface angle
包含表面角度
光照度 E_v 等于发光强度 I_v 除以半径平方。
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Lux

勒克斯

The lux is defined as a lumen per square meter and is a unit of illuminance. An equivalent term is luminous flux density. As such, it measures the amount of visible light striking a surface. The standard symbol for it is Ev. It must take into account the sensitivity of the eye for the wavelengths of light involved, but that is taken care of in establishing the number of lumens.

勒克斯定义为每平方米的流明，是光照度的单位。等效术语是光通量密度。因此，它测量的是照射到表面上的可见光的量。其标准符号为E_v。它必须考虑眼睛对所涉及光波长的灵敏度，但这一点已在确定流明数时得到处理。

An older unit is the footcandle. 1 footcandle = 10.8 lux.

较旧的单位是英尺烛光（footcandle）。1 英尺烛光 = 10.8 勒克斯（lux）。

The sensitivity of some home video cameras allows them to record images in light as low as one lux.

某些家用摄像机的灵敏度允许它们在每勒克斯的光线下记录图像。

Most light meters measure this quantity, and it is the quantity most commonly used to state requirements for architectural lighting.

大多数光度计测量这个量，而这个量是最常用于表述建筑照明要求的量。

Suggested illuminance levels from nzdl

从nzdl建议的光照度水平
 Index

Photometry concepts

Vision concepts

Reference:
Williamson & Cummins
索引 通光概念 视觉概念 参考：Williamson & Cummins
 
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Nit

氮

The nit is the unit of luminance and is defined as a candela per square meter. The unit could be written as cd/m2 or lm/m2sr. It is most often used to characterize the "brightness" of flat emitting or reflecting surfaces. Palmer gives the following examples: laptop computer screens 100 to 250 nits, while those which are sunlight-readable must have more than 1000 nits. Typical CRT monitors are said to have luminances of 50-125 nits.

nit 是光亮度的单位，定义为每平方米坎德拉（cd/m²）或每平方米流明每球面度（lm/m²·sr）。它最常用于描述平面发光或反射表面的‘亮度’。Palmer 给出了一些例子：笔记本电脑屏幕的亮度为 100 到 250 nits，而能够阅读阳光的屏幕必须具有超过 1000 nits 的亮度。典型的 CRT 显示器通常具有 50-125 nits 的光亮度。

The standard symbol for the luminance in nits is Lv.

光亮度的标准符号是L v，单位为尼特。
 Index

Photometry concepts

Vision concepts

Reference:
Williamson & Cummins
索引 通光概念 视觉概念 参考：Williamson & Cummins
 
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