Ever noticed the label of your bulb carefully? You may have noted that its light output is displayed in something called ‘lumens’. In the case of a projector, this rating is measured in ‘ANSI lumens’.
Lumen vs ANSI Lumen
The main difference between lumen and ANSI lumen is that ANSI lumen is standardized by the American National Standards Institute and is more specific and accurate than the lumen which is standardized by the International System of Units.
Lumen (lm) is the SI unit for measurement of luminous flux i.e. the intensity (in candela) of light emitted per solid angle. ANSI lumen is also used to measure luminous flux but is standardized by the American National Standards Institute and an ANSI lumen rating accounts into consideration the aggregate of several measurements taken for the particular light source according to the area of space that it illuminates.
The reason for introducing a new unit in the form of ANSI lumens is that it usually provides a more realistic brightness measurement since it is well structured and based on a greater number of experimental values.
Comparison Table Between Lumen and ANSI Lumen
| Parameter of Comparison | Lumen | ANSI Lumen |
| Symbol | The symbol for lumen is ‘lm’ | ANSI lumen does not have any specific symbol |
| System of units | Lumen is the unit of luminous flux under the SI system of units | ANSI lumen is not an SI unit for measuring luminous intensity |
| Standardization | It is not standardized by ANSI | It is standardized by the American National Standards Institute |
| Accuracy | It is less specific and accurate than ANSI lumen | It is more specific and accurate than lumen since it is based on greater no. of experimental values |
| Applications | It is used for rating lamps and light bulbs | It is used for displaying the light output of projectors |
What is Lumen?
Lumen s derived from the Latin word lumin meaning light. It is the standard unit used for measuring the amount of light intensity across a solid angle of one steradian i.e. it measures luminous flux. Its symbol is ‘lm’. The dimension of luminous flux is [ J ].
1 lm = 1 cd x sr
(cd-calendula: SI unit to measure light intensity
sr-steradian: SI unit to measure solid angle)
Its applications include the rating of the light output of bulbs and lamps including LED lamps, compact fluorescent lamps, as well as incandescent light bulbs. Since 2010, lighting equipment is labelled primarily in terms of luminous flux (in lumens, lm) as an alternative to electrical power (in watts, W).
Illuminance ( in lux ) and luminous flux (in lumens) are the two factors that determine the brightness of a light source. The more is the lux (for constant lumens), the farther is the reach of the light from the source. On the other hand, more are the lumens (for constant lux), more is the brightness of light through a given area.
What is ANSI Lumen?
ANSI Lumens another unit for measuring luminous flux, and is assigned by ANSI-American National Standards Institute but I, not an SI unit. It finds applications majorly in the rating of projectors. The dimensions for ANSI lumen are the same as that for lumen.
It is considered to be more accurate and specific than lumen. The reason behind this is that it is based on a standardized procedure that involves considering an aggregate of several measurements taken t different positions. For commercial purposes, the projectors that undergo this procedure have their luminous flux quoted in ANSI lumens.
Method for measuring ANSI lumens for projectors: The light output of the projector is recorded at nine points around the screen and then its average is calculated.
The product of the average value with the area of the screen gives the brightness of the projector in ANSI lumens. The specification for the ANSI lumen measurement of projectors does not depend on the size of the image that is projected.
Major Differences Between Lumen and ANSI Lumen
- Lumen is the SI unit for the measurement of luminous flux to rate the light output of an artificial source of light, Whereas ANSI lumen is not an SI unit.
- ANSI lumen is described and structured by the American National Standards System which also has a specific procedure to measure the luminous flux but lumen is not standardized by the ANSI
- The symbol for lumen is ‘lm’ but no symbol is defined for ANSI lumen.
- ANSI lumen is more accurate than lumen as it takes into account the average value of flux from different positions of the light source with a set of nine experiments. In contrast to this, the lumen is based on fewer experiments usually involving results recorded from the same position
- Lumen is used to denote the brightness of LED bulbs, incandescent lamps, and compact fluorescent lamps. On the other hand, ANSI lumen is mainly deployed to specify the light output of projectors.
Conclusion
Lumen, meaning light, is a unit used to calculate the luminous flux emitted by an artificial source of light. ANSI lumen is just a more enhanced version of this wherein a standard procedure is adopted to measure the flux by conducting a greater no. of experiments from different positions around the light source that gives better and more accurate results.
Equipment rated using ANSI units is distinguished from those that are tested using other methods which may be less accurate. Despite a difference in their applications, both of these terms are often used interchangeably and have replaced the basis for rating of lighting equipment, which was originally done in watts (W), in terms of the electrical power consumed.
References
- https://iopscience.iop.org/article/10.1088/0026-1394/11/3/001/meta
- https://www.spiedigitallibrary.org/conference-proceedings-of-spie/2650/0000/New-ANSIIEC-standard-for-projectors/10.1117/12.237015.short