## Re: Question

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• Hi, Tracie I m afraid all these technical terms are getting you in a bit of a mix-up. Lux, microwatts per square cm (uW/cm2), lumens (lm), nanometers (nm) and
Message 1 of 18 , Nov 26, 2007
Hi, Tracie

I'm afraid all these technical terms are getting you in a bit of a
mix-up.
Lux, microwatts per square cm (uW/cm2), lumens (lm), nanometers (nm)
and Kelvin (K) are all totally different things, you can't convert
them at all.
It's like asking, how many apples are in a rainbow.

I don't know of any good books on light measurement I'm afraid, and
when I started reading about it, I too found it very baffling. All I
can say is - don't give up! It slowly sinks in, it really does.

Wikipedia is useful, to look up words like lux, light, ultraviolet
and photometry... but sometimes the articles are quite detailed and
challenging. But worth a look.

There are two ways of measuring light.
Wikipedia has helped me out here; it says:
"Photometry" is the science of measurement of light, in terms of its
perceived brightness to the human eye. It is distinct
from "radiometry", which is the science of measurement of light in
terms of absolute power.

When we use the Solarmeter 6.2, we get "radiometry". The measurements
are in Watts, or micro-watts, per square centimetre... they are power
measurements. So you get a reading of, for example, 1 µW/cm² .
You do NOT need to understand all this to use a Solarmeter, and to
use it very accurately. All you need is a steady hand, a tape
measure, and a pencil to write down the readings. Honest.

Wavelengths of light are measured in nanometers (nm). This is not a
measurement of power or brightness at all... I guess the easiest way
to think of it, is that the wavelength is the code number for a
precise colour in the rainbow - a rainbow that includes colours
invisible to us (eg. ultraviolet). So if I said "light of 520nm" I am
talking about light of a very specific colour of green. If I
say "wavelengths between 400nm and 475nm" I am talking about all
colours of purple and blue as a group, from deepest purple to greeny-
blue.

A broadband UVB meter measures all UVB light between wavelengths
280nm and 320nm. It sees how much "power" it's getting from the lamp
from ALL those wavelengths, and gives you a total reading, in µW/cm².

A spectrometer can look at much smaller numbers of wavelengths, eg.
just one or two, and do the same thing. It will tell you, in µW/cm²,
how much "power" it can see at the wavelengths you ask it to look at.

But people like to know other things about a lamp. Our eyes are
not "radiometers" - they see different amounts of "brightness" not
Watts or micro-watts.
So when we measure the "brightness" of a lamp we use "photometry" and
the commonest "photometer" is a lux meter. It looks and works just
like a Solarmeter but the readout is adjusted to make allowances for
how human eyes see "brightness"... the readout is in lux, and refers
to all the visible light. One lux is one lumen per square metre.
(We could write this as 1 lx, or 1 lm/m²)

We also like to know what color light a lamp has. Is it an orangey or
a bluish light? We could look at the power coming out at each
wavelength and calculate it like that.... but you need a spectrometer
and a computer to do "color analysis".
An easier way is to compare the redness or blueness with the glow
from heating something. If you heat a metal bar, for example, it
glows red, then as it gets hotter and hotter, it goes yellow then
white then blue-white. The Color Temperature of a lamp in Kelvin (K)
(which is a temperature measurement like °C) tells you how it
compares with the color of a reference item called a 'black body
radiator' heated to that temperature. Cooler color temperatures (eg,
3,000K) mean an orange glow whereas higher colour temperatures (eg.
12,000K) are bluish. Nice white daylight is about 5,500K to 6,500K.

I don't know whether I've now confused you more... or been of help!
-Frances

--- In UVB_Meter_Owners@yahoogroups.com, "drache613" <JKretzs@...>
wrote:
>
> Hello All,
>
> I have a question regarding lighting measurements. Since we do not
> have a UVB meter yet, I can't do the measurements. I probably
wouldn't
> even know how to do it correctly anyway! LOL Please bear with
me...
> I just wanted to know how to convert or if there is a way to
convert
> uWcm2 to Kelvins?
> For instance, on average a SB 100 watt Megaray has a lux of roughly
> 15,000 to 18,000, (if I looked at the chart correctly) so how would
> that equate to Kelvins? How do I figure Kelvins? I guess I
haven't
> found all of the conversion figures that I need??
> If I did my research correctly, 1 Kelvin equals 683 lux is that
right?
> If so, how many Kelvins does 18,000 lm equal?
> I know how to figure or look to see from Kelvins to nanometers, it
is
> just the Kelvins to lumens I am having trouble with.
> Thanks you for your help.
>
> Yes, I am buying a Spectrometry book for Christmas!! :-))
>
> Tracie
>
• Hello Frances, No, it helps alot! :-)) I wondered if I would be able to convert or not. I guess not! So, do you happen to know if the Megarays have a Kelvin
Message 2 of 18 , Nov 26, 2007
Hello Frances,

No, it helps alot! :-)) I wondered if I would be able to convert or
not. I guess not! So, do you happen to know if the Megarays have a
Kelvin reading on them? The lux you had measured them at was 15,000-
18,0000.
them, so trying to get the "full spectrum" necessary is making sure
that they have between 280-340 nanometers, & 5500-6500 Kelvins so
they can synthesize D3.
It has sunk in about the color spectrum, after studying it now. It
is strange because it goes backwards! I feel dumb, but I have never
really studied stuff like that. I am on the medical end. It just
seems so strange that the Kelvins get lower as the temps get higher.
I am getting a Spectrometry book of some type for Christmas.
I don't know how you put up with me!!

Thanks!
Tracie

--- In UVB_Meter_Owners@yahoogroups.com, "lilacdawndragon"
<lilacdragon@...> wrote:
>
>
> Hi, Tracie
>
> I'm afraid all these technical terms are getting you in a bit of a
> mix-up.
> Lux, microwatts per square cm (uW/cm2), lumens (lm), nanometers
(nm)
> and Kelvin (K) are all totally different things, you can't convert
> them at all.
> It's like asking, how many apples are in a rainbow.
>
> I don't know of any good books on light measurement I'm afraid, and
> when I started reading about it, I too found it very baffling. All
I
> can say is - don't give up! It slowly sinks in, it really does.
>
> Wikipedia is useful, to look up words like lux, light, ultraviolet
> and photometry... but sometimes the articles are quite detailed and
> challenging. But worth a look.
>
> There are two ways of measuring light.
> Wikipedia has helped me out here; it says:
> "Photometry" is the science of measurement of light, in terms of
its
> perceived brightness to the human eye. It is distinct
> from "radiometry", which is the science of measurement of light in
> terms of absolute power.
>
> When we use the Solarmeter 6.2, we get "radiometry". The
measurements
> are in Watts, or micro-watts, per square centimetre... they are
power
> measurements. So you get a reading of, for example, 1 µW/cm² .
> You do NOT need to understand all this to use a Solarmeter, and to
> use it very accurately. All you need is a steady hand, a tape
> measure, and a pencil to write down the readings. Honest.
>
> Wavelengths of light are measured in nanometers (nm). This is not a
> measurement of power or brightness at all... I guess the easiest
way
> to think of it, is that the wavelength is the code number for a
> precise colour in the rainbow - a rainbow that includes colours
> invisible to us (eg. ultraviolet). So if I said "light of 520nm" I
am
> talking about light of a very specific colour of green. If I
> say "wavelengths between 400nm and 475nm" I am talking about all
> colours of purple and blue as a group, from deepest purple to
greeny-
> blue.
>
> A broadband UVB meter measures all UVB light between wavelengths
> 280nm and 320nm. It sees how much "power" it's getting from the
lamp
> from ALL those wavelengths, and gives you a total reading, in
µW/cm².
>
> A spectrometer can look at much smaller numbers of wavelengths, eg.
> just one or two, and do the same thing. It will tell you, in
µW/cm²,
> how much "power" it can see at the wavelengths you ask it to look
at.
>
> But people like to know other things about a lamp. Our eyes are
> not "radiometers" - they see different amounts of "brightness" not
> Watts or micro-watts.
> So when we measure the "brightness" of a lamp we use "photometry"
and
> the commonest "photometer" is a lux meter. It looks and works just
> like a Solarmeter but the readout is adjusted to make allowances
for
> how human eyes see "brightness"... the readout is in lux, and
refers
> to all the visible light. One lux is one lumen per square metre.
> (We could write this as 1 lx, or 1 lm/m²)
>
> We also like to know what color light a lamp has. Is it an orangey
or
> a bluish light? We could look at the power coming out at each
> wavelength and calculate it like that.... but you need a
spectrometer
> and a computer to do "color analysis".
> An easier way is to compare the redness or blueness with the glow
> from heating something. If you heat a metal bar, for example, it
> glows red, then as it gets hotter and hotter, it goes yellow then
> white then blue-white. The Color Temperature of a lamp in Kelvin (K)
> (which is a temperature measurement like °C) tells you how it
> compares with the color of a reference item called a 'black body
> radiator' heated to that temperature. Cooler color temperatures
(eg,
> 3,000K) mean an orange glow whereas higher colour temperatures (eg.
> 12,000K) are bluish. Nice white daylight is about 5,500K to 6,500K.
>
> I don't know whether I've now confused you more... or been of help!
> -Frances
>
>
> --- In UVB_Meter_Owners@yahoogroups.com, "drache613" <JKretzs@>
> wrote:
> >
> > Hello All,
> >
> > I have a question regarding lighting measurements. Since we do
not
> > have a UVB meter yet, I can't do the measurements. I probably
> wouldn't
> > even know how to do it correctly anyway! LOL Please bear with
> me...
> > I just wanted to know how to convert or if there is a way to
> convert
> > uWcm2 to Kelvins?
> > For instance, on average a SB 100 watt Megaray has a lux of
roughly
> > 15,000 to 18,000, (if I looked at the chart correctly) so how
would
> > that equate to Kelvins? How do I figure Kelvins? I guess I
> haven't
> > found all of the conversion figures that I need??
> > If I did my research correctly, 1 Kelvin equals 683 lux is that
> right?
> > If so, how many Kelvins does 18,000 lm equal?
> > I know how to figure or look to see from Kelvins to nanometers,
it
> is
> > just the Kelvins to lumens I am having trouble with.
> > Thanks you for your help.
> >
> > Yes, I am buying a Spectrometry book for Christmas!! :-))
> >
> > Tracie
> >
>
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