[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: halogen lights

> Date: Sat, 7 Aug 1999 22:30:56 -0400
> From: "wayne jones" <waj at mnsi_net>
> Subject: hlaogen lights
> Wright wrote
> >Yes, major concerns. They are way too
> hot and inefficient. About 50% more
> >efficient than regular incandescents,
> they are only about 1/4 as effective
> >(bright) as fluorescent tubes, in
> lumens/Watt. Certainly they are less
> than
> >half as effective for plants.
> How on earth do you know that they are
> inefficient for growing plants? Have you
> ever tried them? 

Yes, I'm using them right now. Doesn't everyone? ;-)

Watt-wise, they are pathetically inefficient compared to discharge lamps
like fluorescents and mercury-halide.

> Do you know the PAR
> rating? 

Roughly. I know the spectrum, which is better, and have enough experience to
know what plants like what light. *Most* plants like the spectrum of
incandescents (including halogens), because they are a good approximation of
sunlight. It just takes five times as much electricity to get the same
number of photons to the plant.

> Luminous efficacy is not a good
> measure of a lamps plant growing
> capabilities. It is true that halogens
> do seem to put out a lot of unnecessary
> heat but what percentage of that
> spectrum is outside the area usable by
> plants.

Major parts of it, of course. That's called infra-red by some and heat by
others. :-) There's even some UV if you remove the protective glass cover
(not a good idea, BTW).

I was one of the first to point out to this list that lumens were not
exactly what plants want. Lumens still are within a factor of two or so for
any broad-spectrum lamp, like "daylight,"  tri-phosphor, C-50 ("sunshine"),
etc. of what the average plant wants. For cool-white, the spectrum, hence
lumen rating, is much farther off. That higher lumens/Watt rating misleads
people into thinking it may be better. It often is not.

> >Don Lancaster has a fun and
> comprehensive lighting tutorial at:
> >http://www.tinaja.com/tinaja%5Findex/gl
> ib/muse95.pdf
> This article is well written and
> humourous but unfortunately is anything
> but comprehensive and has nothing to do
> with the topic at hand. 

It has more to do with the subject at hand than your posting, IMHO. It
explains the visual spectrum and gives comparative efficiency ratings of a
wide range of sources. It also lists a lot of useful resources.

> If you want to
> learn about lighting go to
> http://www.intl-light.com/handbook/index.html  

Glancing at the contents, it looks like a good primmer for the truly
uninformed. I may have been mistaken in assuming that most of the regular
readers knew a little basic science. The Lancaster article summarized
answers to a couple of questions that tend to recur here frequently. It
assumes slightly better science knowledge than is usually imparted by the
mandatory government school system. I agree on that.

Thanks for the lead, Wayne. I'll download all 64 pages and look at it more
closely when I have more time. As an optical engineer, with over 40 years
experience, I tend to assume basic stuff is common knowledge, sometimes.

> In plant growing Lumens/watt can
> be used to measure system efficiencies
> but has almost no bearing on the PAR
> rating of the lamp. 

That's a strong statement. They are very *closely* correlated for most
lights, and only really come apart for lights whose spectrum has been
efficiently tailored to human scotopic sensitivity -- for example, CW

> Yes I know that PAR
> is not the perfect measure of a lamps
> plant growing ability but it is far and
> away a lot better than lumens. 

IMHO, neither should be treated as much more than very rough guides for
aquatic plants. For example, I get better growth out of *Riccia fluitans*,
Watt for Watt, under cool-white fluorescents than any other light. CW lamps
have about the most rotten correlation between PAR (low) and lumens (high)
of any known source. (^_^)

OTOH, a *lower* lumens/Watt rating is a characteristic of broader-spectrum
lamps that plants often prefer, so I don't suggest ignoring it. It is
sometimes a useful clue to the better plant tubes. In general, the higher
the lumens/Watt, the less red and blue growing spectrum from the lamp. Cool
whites are the only one extreme enough to make much real difference, tho,

> As usual
> there is no usable information in the
> article such as radiant power efficiency
> of various lamps or calibrated spectral
> power curves it is all just the usual
> hogwash.

Those are generally available from the manufactureres, in their catalogs,
and were not the subject under discussion (halogen suitability). 

The spectra of incandescent and halogen lights are well known to be pretty
good approximations to blackbody radiation in the photosynthetically
interesting part of the spectrum. That is, fairly flat and uniform from IR
to UV. They are excellent compromises between visibility and action spectrum
for plants. They just waste energy, like mad.

> Wayne Jones
> Stumbling around in the dark as usual


> ------------------------------
> Date: Sun, 08 Aug 1999 00:22:51 -0800
> From: "Thomas Barr" <tcbiii at pacbell_net>
> Subject: RE: halogen lights


> But.................................. the quartz allows you to have an open
> top aquarium. They look very nice compared to many other lighting systems.

Agreed, I love the appearance.........................................but, 

Tom can get away with open-topped tanks in foggy San Francisco, where the
taps deliver nearly distilled water.

In Fremont, the hard-water scale would be horrid, if I tried that, and my
Killies and Bettas would all be dust-balls in no time. [About 80% of my fish
are expert jumpers.]

Since I *have* to cover most small tanks, the problem I have with halogens
is more that the heat actually breaks the cover glass if they are too close!
That's not to mention the water heating that I really don't need here. We
are just across the bay, but average about 20-30 degrees warmer all summer.
The humidity is also way lower.

As always, *everybodys'* mileage may differ. ;-)


Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

         "DEMOCRACY" is two wolves and a lamb voting on lunch.
     "LIBERTY" is a well-armed lamb denying enforcement of the vote.
             *** http://www.self-gov.org/index.html ***