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Science Forum Index » Engineering - Lighting Forum » looking for the incandescent bulb...
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 Posted: Sun May 04, 2008 5:44 pm |
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Hi, All
I am looking for the incandescent bulb with the spectral distribution
as much closer as possible to that of standard CIE illuminant A (CCT
is 2856K). Anyone has the recommendation on this kind of bulb. The
screw-in bulb is preferred. Also I am also looking for the bulb
simulating early morning sunrise and late afternoon sunset
(approximate 2300k). Any help is appreciated. |
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| Don Klipstein... |
| Posted: Sun May 04, 2008 7:32 pm |
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In <f4295e58-b80e-4596-b4d7-254cc460aa15 at (no spam) u6g2000prc.googlegroups.com>,
cyrusli82 at (no spam) gmail.com wrote:
Quote: I am looking for the incandescent bulb with the spectral distribution
as much closer as possible to that of standard CIE illuminant A (CCT
is 2856K). Anyone has the recommendation on this kind of bulb. The
screw-in bulb is preferred. Also I am also looking for the bulb
simulating early morning sunrise and late afternoon sunset
(approximate 2300k). Any help is appreciated.
Illuminant A is easier. As best as I can determine: Get a USA-usual
100 watt 120 volt "A19" incandescent lamp with rated life expectancy of
750 hours and rated light output of 1710-1750 lumens. Apply 119 volts to
it.
With 120 volts, that lamp achieves 2865 K. I see a lot of cites for
2850, 2860, 2865, and 2870, and some of those 2870 figures came from me
back when I tried my own determination. The 2850 ones have some tendency
to be more of a "1-size-fits-all" figure as opposed to being specific to
this specific lamp. I consider 2865 "most credible".
As for sunrise/sunset: Color temperatures vary widely. One widely
spouted figure is 2000 K. My experience suggests much less.
Furthermore, one should consider combination of sunlight plus light from
the sky. My experience suggests that sun-plus-sky onto a horizontal
surface has a high rate of staying close to the color temp. of sunlight
above the atmosphere, and I see various figures for that. I consider 5780
K making a good case for that figure. "Daylight film" is intended for use
with 5500K, or maybe 5500K with removal of UV - so I consider that a "good
figure" for "sunlight plus 'most' of light from blue sky".
But once the sun gets really low, horizontal surfaces see light mainly
from blue sky. Color temp. then goes up.
As for a vertical surface facing a setting sun but also getting light
from the sky: I see color getting flamelike/orange when the color
temperature bottoms out. The 2000K figure widely spouted may be good for
this, though often I see what I would swear is significantly lower.
Please keep in mind that a single number for this may be a
"1-size-fits-all" sort of number!
As for obtaining 2000K from an incandescent lamp: The above 100 watt
lamps achieve that at 47.5 volts. Get yourself a "variac" or other
variable voltage power supply. Be prepared - light output is only about
44 lumens then!
Maybe better to use filtering. To convert the 2865K of a USA-usual 120V
100W 750-hour A19 to 2000K involves a "mired shift" (mired is micro
reciprocal degree) of 151 mireds. "Mired shift" of a filter that works
exactly to convert a specific A to a specific B does not work exactly
anywhere else but it is generally "usefully close". 151 mireds more
orangish is between "3/4 CTO" and "full CTO". A "full CTO" should be
about right with most halogen lamps as well as with 200 watt 750 hour 120V
incandescents.
I just tried firing an incandescent flashlight through a "full CTO" - it
was quite orangish, and a bit more-pink-less-yellow than I usually see
with setting sun. It does appear to me to simulate well lowest color
temp. combination of light from setting sun and sky light on a vertical
surface facing the sun.
Please actually try things and be prepared for widely spouted figures
for daylight conditions to be "somewhat off". Also be prepared for
differences in spectral response among color slide/movie film, digital
cameras, and human eyeballs! Color film can easily have daylight "check
in on the bluish side" unless a UV removing filter is added, while
incandescents and filtered incandescents (whether filtered to lower or
higher color temp.) tend to have less UV than daylight to which the
filtered incandescent is best-color-matched for most human eyeballs. The
only exception I can think of is light from sun close to horizon with
light from the sky excluded.
- Don Klipstein (don at (no spam) misty.com) |
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| Victor Roberts... |
| Posted: Tue May 13, 2008 8:47 am |
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Guest
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On Sun, 4 May 2008 20:44:09 -0700 (PDT), cyrusli82 at (no spam) gmail.com
wrote:
Quote: Hi, All
I am looking for the incandescent bulb with the spectral distribution
as much closer as possible to that of standard CIE illuminant A (CCT
is 2856K). Anyone has the recommendation on this kind of bulb. The
screw-in bulb is preferred. Also I am also looking for the bulb
simulating early morning sunrise and late afternoon sunset
(approximate 2300k). Any help is appreciated.
I haven't seen the SPD of early morning sunrise or late
evening sunset, but I would not expect these to be
Planckian. The sun obviously does not cool off at sunrise
and sunset. The sun looks "reddish" because the light
reaching your eyes has had the blue light selectively
removed by atmospheric scattering to make blue noon-time
skylight for someone 1/4 the way around the earth. That
being the case, no incandescent lamp, no matter what its
color temperature, will match the SPD of the sun,
--
Vic Roberts
http://www.RobertsResearchInc.com
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