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Watts vs lumens
>
>Date: Mon, 15 Mar 1999 16:51:33 -0800
>From: Wright Huntley <huntley1 at home_com>
>Subject: Re: watts vs. lumens
>
>> Date: Mon, 15 Mar 1999 20:16:38 +0100
>> From: "Ole Larsen" <olet at larsen_dk>
>> Subject: watts vs. lumens
>
>snip..
>>
>> Sorry, I donīt know the expression PAR
>
>Photosynthetically Active Radiation. Sounds really nice, but has only a
little
>more meaning than lumens, IMHO. It is defined in terms of the recipient,
and not
>the source of radiation. Unfortunately, the defined "plant" it isn't our
usual
>recipients, aquatic plants and people. ;-)
Dear Wright, Thank you for taking your time to explaine a little of the
meaning of PAR.
Since aquatic plants differ so much, we probably never get a PAR1, that
covers our interest in toto.
>
>> Lumens is a measure of what comes out as light ( candela/steradian) and
thus
>> better, but far from good enough
>
>This statement is quite misleading, and lies at the heart of a lot of the
>misinformation we encounter here on the APD.
Agree, too much malinformation, and fortunately a lot of bright people who
can correct this.:-)
Lumen is a psychophysical term that
>describes the way *humans* perceive optical radiation. Candela is a member
of
>that same photometric system. They are defined in terms of the human
observer,
>and not the source radiation. They tell you next to nothing about what
actually
>"comes out."
Sorry, you broke the connection. What i posted was:
"Watt is only a measure of the energy put into the bulb/tube and
its ballast ect. In no way a measure of what comes out. And the output may
vary as much as 3
times, depending on size, type and temperature
Lumens is a measure of what comes out as light ( candela/steradian) and thus
better, but far from good enough."
And it was a reply to Karen(?) saying the opposit.
And please remark the words " what comes out as light". Light is in my
language "visable".
>Here in APD we define light in a much broader sense, usually.
Would certainly like to know more of the "much broader sense"
Lumens *are* great
>for predicting how bright the light will "look." Too many lumens per Watt
always
>cheats the plants out of energy *they* need,
> for the manufacturers of "cool
>white" tubes have gotten really very good at not wasting red and blue light
we
>don't see well, anyway.
Iīm lost as I do see red and blue. Do you mean they make effords not to
waste infrared and
ultraviolet, we donīt see
>
>Red and blue are about 20% of the output of a very high lumens/Watt tube.
>Unfortunately they are about 80% of the photosynthetically active spectrum
of
>our plants.
īMessed up the percentages ???
That's why plants *can* grow well under "cool white" lights. You
>just may need several times as many Watts of it.
>Wright
>
>- --
>Wright Huntley, Fremont CA, USA, 510 494-8679 huntley1 at home dot com
>
>One big difference between a Libertarian and a Demopublican is the
>Libertarian knows it's not a waste to vote against a Republocrat.
> http://www.self-gov.org/
ole.t at larsen_dk
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