Re: Making pure white light without incandescence -- is it possible?



Green Xenon [Radium] wrote:
[snip]

If all wavelengths of visible light are at equal intensity then why
won't the light appear white?

The theory behind how a luminous source appears to the eye in terms of color, is
very complex. If you really want to find out more, I suggest you start here:

http://ioannis.virtualcomposer2000.com/spectroscope/elements.html
[snip]

What is your interest in such a flat-topped spectrum?

(Interjecting) A flat-top spectrum is what's been called in Lamp Engineering an
"equal-energy" spectrum. Trying to create an "equal-energy" spectrum is
practically impossible, since such a spectrum's distribution is defined by:

I(lambda)={1, iff 380 <= lambda <= 700,
0, otherwise} (1)

where I(lambda) is the spectral distribution intensity of the source at
wavelength lambda. Such distributions (step functions) do not occur naturally as
spectra of light sources. The spectra of light sources instead, are probabilty
distributions, either discrete, or continuous.

In the continuous case (incandescence), you have lots of energy in the tails
left and right of the maximum for the corresponding temperature where this
maximum occurs, so you are waisting energy there. In the discrete case (emission
spectra of the elements) you are having energy in unpredictably sparse areas,
hence as a whole, you are again far from an "equal-energy" spectrum (whith some
exceptions such as Wo, Dy, Xe and Sc, having especially nice and full
distributions [*])

I just want to generate pure white light without wasting most of the
energy as heat.

Definition (1) is used by Rensselaer Polytechnic Institute (ref [35] in the
document above) in an algorithm which calculates what's called a light source
"full-spectrum index". In a sense, the "closer" a source's spectral distribution
is to (1), the "fuller" the spectrum. In other words, the (disguised) question
you are asking, is:

"How can I create a "full-spectrum" light source"?

There is an active debate about what really is a "Full-spectrum" light source.
For starters, see:

http://en.wikipedia.org/wiki/Full-spectrum

For some applications of the "full-spectrum-index" of some light sources, see
section: Lamp Engineering in the above document.

[*] Indeed, some of these elements are utilized as light emitting agents in
various light sources, such as the scandium metal halide, the daylight
dysprosium metal halide and various types of xenon lamps, under different
conditions of temperature and pressure).
--
I.N. Galidakis

.