背投电视（Rear-Projection television, RPTV）是一种大屏幕平板显示电视，是利用反射和投影的方法，将屏幕和投影系统集成一体的电视显示系统。
背投电视
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文章分类：词典
吸光率
吸收系数
定义
描述物质（内部）吸光率的一个指标。如果该物质的单位透射量是 t，吸收系数（a）就是：
a = 1 – t
English Expresstion
absorption coefficient
Definition
An indicator of a material’s internal absorptance. If the unit transmission of the material is t, the absorption coefficient (a) is:
a = 1 – t
吸收比
定义
吸收光辐射或光通量与入射光辐射或光通量的比。
English Expression
absorptance
Definition
Ratio of the absorbed radiant or luminous flux to the incident flux.
绝对白色
定义
只作为一个概念存在的理想扩散体，或者在测量绝对反射率时作为参考的具有已知光谱特性的白色。
English Expression
absolute white
Definition
A perfect diffuser that exists only as a concept, or a white with known spectral characteristics used as a reference in measuring absolute reflectance.
绝对温标
定义
以Lord Kelvin命名（1848）的热力学温标。该温标以“开尔文（K）”作为温度单位。（在SI（国际单位制）中，不用度的符号以及“度”这个词来表达开氏温度。）温度的绝对零度是零K，或 -273.16 °C （摄氏度），或 -459.7 °F （华氏度）。开尔文单位的大小（一度）与摄氏度的是一样的。
English Expression
absolute temperature scale
Definition
Thermodynamic temperature scale, named for Lord Kelvin (1848), in which temperatures are given in kelvins (K). (In the SI system, the degree sign and the word degree are not used for kelvin temperatures.) The absolute zero of temperature is zero K, or -273.16 °C (Celsius or centigrade), or -459.7 °F (Fahrenheit). The size of the kelvin unit (degree) is the same as that of the Celsius degree.
绝对折射率
定义
介质相对于真空的折射率。
English Expression
absolute refractive index
Definition
The refractive index of a medium in relation to that of a vacuum.
焦距
定义
有效焦距（EFL）是指主点到焦点的距离。
后焦距（BFL）是指最后一片透镜的顶点到第二焦点的距离。
前焦距（FFL）是指第一片透镜的表面到第一焦点的距离。
English Expression
focal length ( f )
Definition
The effective focal length (EFL) is the distance from the principal point to the focal point.
The back focal length (BFL) is the distance from the vertex of the last lens to the second focal point.
The front focal length (FFL) is the distance from the first lens surface to the first focal point.
绝对放大率
定义
透镜放大率的一种表达方式，等于明视距离（250 mm）除以等效焦距。绝对放大率是指当物体位于透镜焦点的时候产生的放大率。
English Expression
absolute magnification
Definition
The magnification equal to the distance of distinct vision (250 mm) divided by the equivalent focal length of the lens. Absolute magnification is produced when the object is at the focal point of the magnifier lens.