From: tse@ra.nrl.navy.mil (Anthony Tse)
Subject: Re: Information about lights
Organization: Naval Research Lab, Washington, DC
Date: Sun, 22 Nov 1992 05:00:10 GMT

In article <2520051@hplvec.LVLD.HP.COM> booth@hplvec.LVLD.HP.COM (George Booth) writes:
>I'm also not sure about how color
>temperature affects its accuracy.  Its response curve peaks at about
>600 nm, so there is probably some effect.

	That will surely affect your data if you are interested in PAR
output, specially for reef application where red light is pretty
useless.  However, it will give a good indication on how bright the bulbs
are.

>
>To measure color temperature, I rented a Minolta Color Meter II from a
>photographic supply store in Denver.  It's primary use is to determine
>the correction filters required to balance a specific film for a
>specifc light source, but it also indicates color temperature in
>degrees Kelvin.  I'm not sure of its absolute accuracy (and I did see
>some strange results with metal halide lights), so take the numbers
>with a grain of salt.  This is a neat instrument that sells for about
>$700, so I feel that numbers aren't too far off for the fluorescent
>bulbs.  Minolta also makes a different meter for "scientific and
>industrial colorimetery", but it's not available for rental locally.

	The Minolta Color Meter II should be fairly accurate since a few
hundred degrees off can really screw things up if you are a pro
photographer shooting slide.  I can't explain why you got such strange
color temperature reading.  A few things can possibly affect the reading,
room light and color of the reflector came to mind, a white reflector to
most people is not white to a photographer who is willing to pay $700
for a meter to check color temperature.  But some of your readings are
really really strange.  There exist widgets that measure spectral ouput
of lamps and give you a plot of output power vs wavelength.  I think we
actually have one here at the lab, but I don't think they want me to
haul in a bunch of flourescent lamps and measure them, it's much eaiser
to call the lamp manufacturers and ask them to send you their
measurements, assuming you are buying "normal lamps" where companies like
Phillips, GE, OSRAM, etc will gladly mail or fax you any info you want.


>This posting is the raw data I collected.  I have not as yet drawn any
>conclusions aside from obvious things like Penn-Plax Ultra TriLux
>bulbs are brighter than Triton bulbs and they have a color temperature
>closer to sunlight (whether or not that is good, I'm not saying). 

	Color temperature has very little to do with how close the spectral
output of a bulb is to sunlight.  Sunlight has a continious spectrum
across the visible spectrum, whereas a 5500K (or 6500K or whatever)
triton has 3 narrow spikes, one in blue, one in green and one in red.
The human color visual system consists of three overlapping bandpass
filters, one center at blue, one at green and one at red, our brain
takes the AMPLITUDE output of these three filters and assign a color to
it, that is why you can create any color with three monochromatic
sources (RGB or CYN) for the HUMAN VISUAL system by varying the relative
amplitude of the three colors.  And since photographs are for humans to
look at, all the color meter care about is the relatively amplitude
output of the three bandpass filters, it doesn't care whether or not the
bulb put out a continious spectrum, it certainly doesn't care whether or
not the three color spikes coming out of all these tri-phosphorous bulbs
are usful for plant growth or not.  So a picture that look perfectly
good to us human under a 5500K triton will look completely out of wack
to other species with different sets of color filters.  In short, an
AX50 has one output spike at 430nm, one at 540nm and one at 620nm and
these three spike combine to give you a 5000K color temperature, but if
photosynthesis occur between say 470nm to 500nm (which are not correct
numbers), then the AX50 will be useless for plant growth even though it
has the right color temperature.  In conclusion, your safest bet is to
use bulbs such as vita-lite (which I know most people don't like because
it is not "white" even thought the spectral output of a vita-lite is
about as close to the sun spectral as one can get, and because sales
critters can make more money by selling you "reef bulbs" whose spectral
output are nowhere close to the sun's spectrum).  Chroma50 and Chroma75
are also safe bets because they are vita-lite with a extra blue
spike.  I use the words safe bet because the vita-lite and the chroma
bulbs best simulate sun light and plants and corals just happen to live
under the sun.  For all I know, plants and corals maybe perfectly happy
living under blue actinic light as long as you have enough of it to
satisify their photosynthetic need.  The choice between using full spectrum
bulbs or tri-phos bulbs is yours, I have one tank lit with ColorTone50s
(Phillips verson of Chroma50) and actinics, another tank lit with
tri-phos compact flourescents (the 40W job, not the little 9W thing)
and actinics, I much prefer the ColorTone50 tank even though the
tri-phos compact flourescents are much brighter (almost as bright as
the AX50 per watt).

>I was very surprised at the rapid initial drop off of intensity from
>the MH bulbs; I had expected a linear drop for most of the lifetime. 
>The data indicates that MH bulbs should be changed once a year if
>you have intensity sensitive applications.

    I posted this about a year ago and got everybody really upset
because I was telling them they've been fooled by all the sale hype of
MH.   Anyone can call OSRAM and get them to fax you data sheets on their
MH.  The Lumen Maintenance curve furnished by OSRAM on their 250W 5400K
MH clearly shown that MH lumen drop off extremely fast and not linearly.
The output drop to 70 percent of initial after ~3000 hours and stay
there until the bulb burn out.  But of course, the advistised lumen
output are always initial lumens which will last maybe a couple of
hours.  Flourescent lamps on the other hand drop at a MUCH slower rate,
for example, an Ultralume will maintain 95% of its initial output after
3000 hours and 80% of its initial output after 26000 hours.  How the
statement "flourescent lamp became noticably dimmer after 6 months
and need replacement while MH will maintain their output for much longer
thus only need replacement every two years" came about is beyond me.
Even the actinic03 will maintain 80% of its initial output after 3000
hours.  And if a stock OSRAM 9W blue bulb is 5 times brighter then the 40W
actinic03, then I must have a very serious eye problem, cause my
moon light is a 9W OSRAM blue and it's nowhere near as bright as a
single actinic03.


-Anthony

PS One of these days I will control myself and stay out the lighting
discussions.
-------
Disclaimer:  Those are my opinion and mine alone.  They have nothing
to do with the company I work for.
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