Whats the difference between the white light bulbs and yellowish tinted light bulbs what makes the color yellowish? Do they both emit multiple wavelengths of all the colors or does one of them emit different wavelengths than the other?
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$\begingroup$ What kind of bulbs? Filament? LED? Halogen? $\endgroup$– Marius Ladegård MeyerCommented Apr 10, 2023 at 7:17
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$\begingroup$ Filament @MariusLadegårdMeyer $\endgroup$– Flora561Commented Apr 10, 2023 at 7:25
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$\begingroup$ Sodium-vapor lamp? $\endgroup$– HolgerFiedlerCommented Apr 11, 2023 at 3:17
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2 Answers
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Colours are only a result of our perception, not some fundamental physical reality.
Every light source can be treated as if it emits a full spectrum: to each wavelength we can assign some total spectral flux. With some sources this might be only several several discrete lines, but that can still be treated as a function defined on all positive wavelengths. Both of the bulbs emit a full spectrum, but they differ in the ratios of different wavelengths in it.
Simply put, in a human eye there are (usually) three types of cone cells (S, M and L). These roughly correspond to the blue, green and red part of the visible spectrum. Each continuous spectrum can be reduced to three numbers, which describe the responses of the respective cone cell types. We may denote these tristimulus values $S$, $M$ and $L$.
Neutral white is obtained when their ratios are roughly the same as with natural sunlight, or a black-body with temperature about 6500 K. If one of the bulbs emits less blue light than this, the eye's $S$ response to its light is lower and it appears yellowish.
In reality, it is much more complicated though: human eyes/brain are able to adapt to a different white point to some extent over time. If you spend some time with the yellowish bulb on, you will start to perceive its light as white. Now if you turn on the other one on, it will appear bluish.
answered Apr 10, 2023 at 10:53
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$\begingroup$ Could be helpful to add that the response curves of S, M, and L cells are broadly overlapping, and our perception of color depends on the ratios of stimulation of the different kinds of cell. $\endgroup$ Commented Apr 10, 2023 at 11:47
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$\begingroup$ @SolomonSlow Agreed. However I mention the ratios – more precisely, that would be chromaticity rather than colour. But I'm afraid that an exhaustive explanation would be exceedingly long... even at my level of understanding, and I am an astronomer, not a colour professional. $\endgroup$ Commented Apr 10, 2023 at 11:56
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Each light bulb is a point in the chromaticity diagram. To determine if a light bulb is white, you need to determine whether the point is close to the white point in the chromaticity diagram. The white point depends on the ambient light. If the light source of the ambient light is known, you can find the white point here.
