In finally want to know, what blackbody temperature is exactly white?

Question

Now really, it should be impossible for a blackbody to be completely white right, because the dropoff on the blue side is steeper than the dropoff on the red side.

So there's no way to equally stimulate all three cones at once -- (other than saturating them, which is kindof cheating)

Anyway, there still must be a closest.

What temperature would be closest to white ?

I think it's somewher between Sun temperature and D65

Answer 1

Answer: Somewhere between 5000-6500K but nearer to 6500K.

It is well known that when an object, such as a lump of metal, is heated, it glows; first a dull red, then as it becomes hotter, a brighter red, then bright orange, then a brilliant white. Although the brightness varies from one material to another, the colour (strictly spectral distribution) of the glow is essentially universal for all materials, and depends only on the temperature. In the idealised case, this is known as 'black body' or 'cavity' radiation, and is described by Planck's Radiation Law:

Spectral energy density, U(λ,T) = 8πhcλ-5 / ( ehc/λkT-1 )

where

λ is the wavelength, in metres
T is the temperature in Kelvin (add 273 degrees to Celcius temperatures to get Kelvin)
h = 6.626×10-34 J·s [Planck's constant]
k = 1.381×10-23 J·K-1 [Boltzmann's constant]
c = 3.0×108 m·s-1 [speed of light]
For any more detail, see an undergraduate-level Physics textbook!

The figure below illustrates the relative amounts of energy at each wavelength across the visible spectrum, for a 'black body' at 3200K, 5000K, 6500K, and 9300K. A conventional incandescent light bulb emits light (and heat!) from a tungsten filament heated to high temperature by passing an electric current through it. Spectral distribution (including colour) of the light from a quartz-halogen lightbulb is similar to a black body source at 3200K, and is therefore well-approximated by the Planck Law. Light from the sun, measured in space, is close to black body radiation characteristic of temperatures around 5000-6500K.

In physics, a black body is an object that absorbs all electromagnetic radiation that falls onto it. No radiation passes through it and none is reflected. It is this lack of both transmission and reflection to which the name refers. These properties make black bodies ideal sources of purely thermal radiation. That is, the amount and wavelength (color) of electromagnetic radiation they emit is directly related to their temperature. Black bodies below around 700 K (430 °C) produce very little radiation at visible wavelengths and appear black (hence the name). Black bodies above this temperature, however, begin to produce radiation at visible wavelengths starting at red, going through orange, yellow, and white before ending up at blue as the temperature increases.

The wavelength at which the radiation is strongest is given by Wien's displacement law, and the overall power emitted per unit area is given by the Stefan-Boltzmann law. So, as temperature increases, the glow color changes from red to yellow to white to blue. Even as the peak wavelength moves into the ultra-violet enough radiation continues to be emitted in the blue wavelengths that the body will continue to appear blue. It will never become invisible — indeed, the radiation of visible light increases monotonically with temperature.
Some common examples.

1700 K: Match flame
1850 K: Candle
2800 K: Tungsten lamp (incandescent lightbulb)
3350 K: Studio "CP" light
3400 K: Studio lamps, photofloods, etc...
4100 K: Moonlight
5000 K: Daylight
5500 K: Average daylight, electronic flash (can vary between manufacturers)
5770 K: Effective sun temperature
6420 K: Xenon arc lamp
6500 K: Daylight°
9300 K: TV screen (analog)

5000 K and 6500 K are also called respectively D50 (US standard) and D65 (Europe standard) in all professions working with light (photographers, publishers, etc.). It is a temperature similar to black body temperature but not strictly identical.
The power of a lightbulb (20 or 100 W) seems to change its color but in reality it only affects its luminosity (luminance) to which our eyes are very sensitive.

From these observations, it becomes clear for all colors based on the black body that blue is the "hotter" color, while red is actually the "cooler" color. This is the opposite of the cultural associations both colors have taken on, with "red" as "hot", and "blue" as "cold". The traditional associations come from a variety of sources, such as water and ice appearing blue, while heated metal and fire are of a reddish hue. However, the redness of these heat sources comes precisely from the fact that red is the coolest of the visible colors: the first color emitted as heat increases. To see this, observe that while incandescent bulbs glow a reddish to yellowish color throughout their lifetimes, when one blows out, the flash of light is noticeably bluish - the filament is hotter when it burns out, as evidenced by the scorch mark often left on the glass.

"Color temperature" is sometimes used loosely to mean "white balance" or "white point". Notice that color temperature has only one degree of freedom, whereas white balance has two (R-Y and B-Y).

Answer 2

ok, i'm now no longer protecting it incredibly is the genuine answer besides the reality that this is wise to me. First the earth warms up, melting the ice sheets on the north pole. The clean water rushes into the sea shutting down the gulf bypass ocean modern-day which transports heat temperature from the equator to the the north atlantic. Temperatures interior the northern hemisphere start to drop and are lined in snow and ice. The snow and ice mirror the image voltaic radiation from the image voltaic back into area and the earth keeps to relax. over the excellent ice age this is pronounced that the everyday international temperature replace into 18 stages cooler than this is now. Ice a mutually as are perfect climate undertaking. As evidenced by using the geological historic previous which shows that the everyday ice age very final around a hundred,000 years at the same time because of the fact the international warming instructions inbetween very final in straightforward terms approximately 10,000 years. this is been actual approximately 12,000 years by actuality the excellent ice age, greater advantageous useful get a coat.

Answer 3

"White" is a subjective impression, not a scientific definition. Sunlight (color temperature ~5600K) is probably the truest white, just because that's what our eyes and brains have evolved with. But your brain tends to perform an automatic "white balance" - any broad-spectrum light source will appear white if it's the dominant light source and its color balance doesn't skew too sharply towards one end of the spectrum.