In this case, it is often instead called the luminous efficiency, and may be expressed as a percentage.

For example, a typical incandescent light bulb has a luminous efficiency of only about 2%.

Luminous efficiency, that portion of the emitted electromagnetic radiation is usable for human vision.

Color and Research Vision Laboratory - luminous efficiency data tables

No real display device uses such primaries, as the extreme wavelengths used for violet and red result in a very low luminous efficiency.

The following table lists luminous efficiency of a source and efficiency for various light sources:

Within the visible spectrum, wavelengths of light are weighted according to a function called the "photopic spectral luminous efficiency."

One of the key advantages of LED-based lighting sources is high luminous efficiency.

Luminous efficiency

The Eagle also featured new technology to improve luminous efficiency of its headlamp system, afford greater styling freedom, and having a rectangular frontal aspect.

Two very similar measurement systems were created to bridge the scotopic and photopic luminous efficiency functions, creating a unified system of photometry.

The ratio between the actual number of lumens per watt and the theoretical maximum is expressed as a percentage known as the luminous efficiency.

Often, higher efficiency will mean lower color rendering, presenting a trade-off between the luminous efficiency and color rendering.

However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficiency.

The luminosity function or luminous efficiency function describes the average spectral sensitivity of human visual perception of brightness.

The luminous coefficient is luminous efficiency expressed as a value between zero and one, with one corresponding to an efficacy of 683 lm/W.

Because most people have a point of maximum luminous efficiency that is off-center, the Stiles-Crawford Effects generally will have antagonistic chromostereoptic effects.

In 1951, the International Commission on Illumination (CIE) established the scotopic luminous efficiency function, V'(λ).

The dimensionless luminous efficiency measures the integrated fraction of the radiant power that contributes to its luminous properties as evaluated by means of the standard luminosity function.

The color matching function would be exactly equal to the photopic luminous efficiency function V(λ) for the "CIE standard photopic observer".

Full cutoff streetlights also reduce light pollution by reducing the amount of light that is directed at the sky which also improves the luminous efficiency of the light.

The integrals of the XYZ color matching functions must all be equal by requirement 3 above, and this is set by the integral of the photopic luminous efficiency function by requirement 2 above.

In 1924 it established the standard photopic observer defined by the spectral luminous efficiency function V(λ), followed in 1951 by the standard scotopic observer defined by the function V'(λ).

There are many non-incandescent light sources, such as the fluorescent lamp, high-intensity discharge lamps and LED lamps, which have higher luminous efficiency, and some have been designed to be retrofitted in fixtures for incandescent lights.

The combination of these properties yields a mantle that, when heated by a kerosene or liquified petroleum gas flame, emits intense radiation that is mostly visible light, with relatively little energy in the unwanted infrared, increasing the luminous efficiency.