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LED (light emitting
diode) lighting is one of the latest lighting technologies to emerge in
the hobby, and one that I'm excited about. LEDs are vastly more
efficient that other types of lighting, produce much less heat, and if
high quality electronics are used and effective cooling is used, last a
very long time without losing much output. Whenever a new lighting technology comes along,
hobbyists tend to attempt to compare it to a previous and more familiar
technology. This time around, LEDs are getting compared to metal halide
lighting a lot, but it just doesn't work. We all know we don't
exactly use the scientific method in our hobby. Terms such as watts per
gallon, intensity, and brightness get thrown around all of the time,
even though they mean absolutely nothing useful to us or our coral. So,
what's to be done? In fact, LEDs can't even be compared with the
use of a PAR meter (the PUR of the diode is what's important!)!
However, I'm digressing from the point: the point is that using MH
as a tool in which to compare LED lighting to is misleading.
MH lighting is a 'single point source
light', meaning all of the light is emitting from one source in one
location (in contrast, a fluorescent tube is a single source, but the
light is emitted from the entire tube, not from a single point). LED
lighting, however, is 'multiple point source' lighting, which
means several sources emit light from a single point. This is a huge
difference in terms of how the light is spread in an
aquarium! While MH lighting can be modified with a variety
of reflectors to form a spotlight or to cover a large area very
uniformly, LEDs are limited by their optics. Common optic reflection
degrees are 45, 60, 90, and 120, with 45 appearing as a concentrated
spotlight and 120 giving the most uniform coverage. Additionally,
coverage can be (and often must be) adjusted by altering how high the
LED fixture sits above the water's surface. Of course, wider
coverage means less water penetration. Unlike MH lighting, with is
excellent for both spread and depth penetration, LED light must be more
tightly focused to accomplish this--again, because of it's multiple
point source nature. If you are not familiar with LED lighting,
purchasing the appropriate unit for the coverage you want at the height
you want can be difficult--don't expect it to be as simple as
purchasing MH lighting. However, the benefits of LED lighting are many,
so don't let this discourage you! Check the manufacturer's
website or reviews to see coverage recommendations, and while
you're at it, check the spectrograph (don't buy an LED product
if the manufacturer doesn't provide you with the spectrograph!).
They should be willing to work with you, or take your business
elsewhere.
Another complaint often heard from those
making the switch is 'my new LEDs aren't as 'bright' as
my metal halides were!' ('bright', in this case, referring
to the relative luminosity of the light, or how it looks to your eyes);
even though the LEDs likely emit at least as much or more PUR as the
prior MH source. This has to do with the way the human eye
sees: different spectrums appear 'brighter' (more luminous)
than do others. LEDs, especially ones used in aquarium fixtures, emit
(or should emit) a great deal of PUR. However, most of the PUR for
photosynthetic inverts like coral is not in the spectral range that the
human eye views has highly luminous, meaning that the light appears
dimmer to our eyes, even though it could be emitting more PUR for your
coral than did the MH bulb.
You can see from the image above that the
human eye is not very sensitive to light in the blue wavelength (only
about 12% of our color receptors respond to blue wavelengths) and as
high PUR LEDs emit a great deal of their light energy in the blue
spectrum, they appear less 'bright' than do other forms of
light that emit more green or red. 'Brightness' (luminosity) is
relative, and means nothing to coral! Want a brighter look? Use LEDs along with
another form of lighting, or purchase wide angle LEDs with LED
spotlights to produce dramatic effects with light and shaded areas.
More 'shadowing' may occur with LED lighting than the aquarist
is used to seeing, because each LED functions essentially as a
miniature spotlight (not to be confused with LED spotlight fixtures),
and LED light will not be as uniform in it's distribution as MH
lighting is by nature of design. Although, have you been to a reef
recently? Believe me, they're not uniformly illuminated. Once you
become accustomed to the 'dynamic' way that LEDs illuminate an
aquarium, you won't want to go back! In closing, LED a very promising technology
and is most definitely the lighting of the future, and not only for
aquariums. Keep in mind that LED lighting is still very new, and there
has been an explosion of fixture models and a few different diode
models from which to choose, which can be confusing. Many of the new
LED fixtures are very cheaply made, so research before purchasing, but
don't be afraid to make the switch! |
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