In message <***@nospam.demon.co.uk>, Kate Brown
Post by Kate Brown
Indeed. I like the idea of low-energy lighting too. But apart from
the delay (still noticeable even in the fastest ones I've found) the
main reason we don't use many of them is the horrible light they give.
Even though they claim it's equivalent either to daylight or tungsten
(depending on whose blurb you read. Mostly they refer to a colour
temperature of 2700, whatever that actually is), the light itself is
distinctly greenish, and renders anything yellow or red - anything
cheerful! - muddy. Very depressing, as our hall and stairways are all
a lovely primrose yellow that goes a nasty dull acidic colour. People
too, as you point out, also look decidedly off-colour.
Colour temperature: equivalent "black body" temperature. If you draw a
graph of wavelength of emitted light against intensity of same, you get
something with a spiky spectrum in the case of a pure discharge tube
(like the old sodium streetlights, or neon or other "coloured" tube
lights); if you heat a body to a certain temperature (either by playing
a flame on it, or heating it directly as in the case of a tungsten
filament), you get a broader spectrum, but the centre of the spectrum is
still based around somewhere (redder for cooler, bluer for hotter). The
"colour temperature" is the equivalent temperature you'd have to heat
something to to make it glow in a particular manner (I can't remember if
it's Celsius or Kelvin). Fluorescents - both the old striplights and the
modern compact ones - are basically discharge tubes, which emit a narrow
peak (often in the ultraviolet), with a "phosphor" - a powder - on the
inside of the tube, which when exposed to ultraviolet light, glows in
the visible spectrum. They try to use a mix of phosphors that mimics the
normal black body type of light. The colour temperature is the
temperature of the black body they're claiming to mimic.
The eye has only three types of colour sensors (basically red, blue, and
green), and additionally the brain adjusts anyway. (You can demonstrate
this by exposing yourself [!] to strongly coloured light for a while,
then going into more neutral lighting; I remember at school, the main
hall had heavy red curtains. Once or twice I'd been in there for a while
on a very sunny day, but with the curtains drawn for some reason - play
rehearsals or something; when I came out into central hall, the world
seemed most disconcertingly green for a few minutes!). Therefore, if you
have mainly white or creamy walls, the lighting doesn't matter that much
- except that, some of the things you might want to look at (including
people!) have a colour mix that doesn't match the spectrum of the
artificial source (its peaks are in the gaps of the source or whatever),
so look decidedly odd.
LED lamps - which are still expensive - have a fairly narrow spectrum,
and are mostly still just used where a coloured lamp is actually wanted.
So-called white ones are actually blue LEDs with phosphors in them, like
fluorescents, which glow in an approximation to white again.
Sorry, I got carried away there! I think I'm a teacher underneath (well,
both my parents were, though language [briefly mentioned in
http://en.wikipedia.org/wiki/Peter_Gilliver, pictures on
www.soft255.demon.co.uk]), especially on science subjects.
J. P. Gilliver. UMRA: 1960/<1985 MB++G.5AL(+++)IS-P--Ch+(p)Ar+T[?]H+Sh0!:`)DNAf
** http://www.soft255.demon.co.uk/G6JPG-PC/JPGminPC.htm for thoughts on PCs. **
Essex home for sale, œ59,950: see http://www.soft255.demon.co.uk/home/
10.0 times 0.1 is hardly ever 1.0.