This subjectivity contrasts with the standardized definition of temperature, which is measured by instruments in degrees Celsius. When describing temperature with the terms “hot” or “cold”, there is no standardized definition of “hot” or “cold” and the perception of these terms can vary greatly from person to person. The HK Effect and “LED Lumens” are based on perception. The analogy to temperature can be used to illustrate this. Brightness is a matter of perception, unlike lumens, which is a measure of luminous flux, an observer-independent quantity that can be measured with standard instruments. Importantly, the term HK effect refers to apparent brightness. Perhaps for this reason, the reported benefits of the HD effect range from 1,3x to 2,4x, which is a wide range. Standardizing a purported HK benefit for apparent brightness is challenging because the HK effect depends on the viewer*, ambient lighting conditions (luminance and color matching), the saturation level of the content being displayed, and other factors. Regardless of the type of light source used, the same internationally recognized method of measuring a projector's light output can and should be used.ģ) There is no standard for measuring the Helmholtz carbon effect. white light for room lighting, spotlights and LCD backlighting. Also, LEDs are not necessarily saturated: LEDs can also produce a wide spectrum of light, e.g. LEDs are not the only way to create saturated light. These sources include saturated LEDs, but also lasers, phosphor-converted light sources, and quantum dot-converted light sources. Although certain projection manufacturers may want to promote their particular technology, there are several methods of creating narrow bandwidth, highly saturated light sources for a projected image. Not surprisingly, the term "LED lumens" is only used by certain projector manufacturers who have chosen LEDs as their light source. “LED lumen” has never been standardized.Ģ) “LED Lumens” is not an industry accepted term It is misleading to use the term "LED lumens" instead of or in addition to ANSI or ISO lumens, the methodology of which has been standardized and published by several accredited and internationally recognized organizations. Importantly, there is no known standard for measuring so-called “LED lumens”. The term “LED lumens” is placed in quotation marks throughout this report because it is a marketing term. The reader should be aware of a few points of this manufacturer's misleading white paper: The paper further claims and applies an unsubstantiated light output factor based on the perceived color saturation of the chosen light source, multiplying the standardized lumen rating by a factor of 2,4 to arrive at the "LED Lumen" rating. This paper describes an aspect of human perception, the Helmholtz-Kohlrausch (HK) effect, which allows saturated colors to appear brighter. One manufacturer even wrote a white paper entitled "Understanding the difference between ANSI Lumen and LED Lumen". Recently, the term "LED Lumen" has been popping up in marketing materials. In addition, this method has been used consistently for more than two decades. As a result, the industry has settled on the standardized method for measuring the lumen output of a projector. The same methodology was also adopted by the International Electrotechnical Commission (IEC) in IEC 61947-1, published in 2002 and in a more recent IEC document, 6, published in late 2021, and the same basic methodology is also found in ISO 21118, originally published in 2005 and most recently re-published in 2020. In the industry, the term "lumen" is used for this method, which is still used today for the light output of a projector. Standardized method for measuring the light output of projectorsīecause of the importance of having a standardized method of measuring a projector's light output, the American National Standards Institute (ANSI) published ANSI IT1992 in 7.215, which was updated to ANSI IT1997 in 7.228. The important point is that a projector's lumen rating refers to the amount of optical power that the projector can deliver to the screen. The difference is that radiant flux is related to broad spectrum power, while luminous flux is radiant flux weighted according to the spectral sensitivity of the human human eye, i.e. Lumens are dimensionally equivalent to watts, a unit of power that is analogously related to radiant flux. Projector light output is measured in lumens, a unit of luminous flux. Distributors, retailers and consumers compare manufacturers' light output because light output is a key factor in a projector's display performance. In the highly competitive world of projection devices, the light output of a projector is an important purchase criterion.
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