Qualities of Various Fluorescent Lamps
Text and Photo by Dana Riddle
Water off the Kailua-Kona, Hawaii coast is usually clear, and
blue, at a depth of 10 meters.
There exists in many serious
hobbyists the paradoxical desire to create a natural environment via artificial
means. This artificial ecosystem would mimic the composition of seawater,
the water motion created by wind and tides, temperature, and of course, the
intensity and spectral qualities of sunlight as it is ‘filtered’ by clear
We occasionally read in hobbyist
literature advertisements for lamps that claim to artificially replicate light
quality found at certain depths on natural coral reefs. This article
will examine spectral quality of various fluorescent lamps available in the US
and Europe, and will compare these with various qualities of natural sunlight.
This information may be useful to those purists wishing to mimic light quality
found in the most optically transparent (‘clearest’) oceanic water, such as
those reef crests dominated by small-polyp stony corals.
Fluorescent lamps have been a staple
in the hobby for many years and occasionally new variations are introduced to
the market. Such is the case with the recent introduction to the US market of
‘T-5’ fluorescent lamps. This article will examine qualities of some of the
‘newer’ T-5’s, as well as tried-and-true work-horse fluorescent lamps –
especially that of spectral quality and, to a lesser degree, light intensity
(photosynthetically active radiation, or PAR).
Introduced in the early 20th
century, fluorescent lamps are a popular choice for lighting reef aquaria.
They are available in a wide range of sizes and wattages. Wattage measures
the electrical consumption of a lamp, not it's light output. For
fluorescent lamps, lumen output per watt of energy is about 2.5 to 3 times that
of incandescent lamps. Lamp life is also generally much longer (as much as
20X that of incandescent lamp).
Fluorescent lamps are tubular glass
envelopes containing argon (or krypton), mercury and selected phosphors.
Supplying adequate current to electrodes at the ends of the tube generates an
electrical arc resulting in production of invisible ultraviolet (UV) energy,
which excites the phosphors. These phosphors absorb the ultraviolet
energy and emit (fluoresce) it as visible light. Mixtures of phosphors
within fluorescent lamps produce various light qualities. Phosphors
that produce blue wavelengths include calcium tungstate and strontium
chloroapatite. Blue-green and green are produced by barium titanium
phosphate and zinc sulfate, respectively. Magnesium fluorogermanate
produces red wavelengths (IES, 1984). The element mercury (Hg) also lends
spectral quality to the lamp’s output. Mercury produces many spectral
lines - of most interest to hobbyists are those narrow spectral bands at 365 nm
(UV-A), 405 nm (violet), 435 nm (blue), 547 nm (yellow-green), 577 nm
(yellow-orange) and 579 nm (yellow-orange).
“Triphosphor” lamps have recently
appeared on the market. This formulation of phosphors enhances
greens and reds. Triphosphor lamps have varying degrees of light
production in the following portions of the spectrum: violet/blue, blue-green,
green-yellow and orange-red. Most Compact Fluorescent lamps
presently on the market are tri-phosphor lamps (except for ‘blue’ and ‘actinic’
Most fluorescent lamps are most
efficient at about 25°C (77° F); however, they are designed to operate at about
~38º C (100°F). Light generation drops about 1% for every 1° C rise
in temperature above 25° C. Internal pressure of the lamp is
directly related to light output; pressure is sensitive to temperature.
A small fan might serve too purposes – light output is potentially increased if
lamps are cool and heat transfer to the aquarium water is decreased.
Markings on Fluorescent Lamps
Fluorescent tubes are generally
marked with information at one end of the lamp. The ability to
interpret these markings will provide valuable information.
Generally, the first marking
designates the manufacturer or marketing agent. Examples include
Osram, URI, Coralife, ZooMed, etc. The next marking usually
indicates the type of lamp. Common markings for fluorescent lamps
are “F”, “FR” for standard tubular lamps; Compact Fluorescent lamps are usually
marked with “TT” or “PL,” depending upon manufacturer. These
markings are followed by a number indicating wattage. Tubular lamps
are marked with the diameter, usually as a “T”, followed by a number, indicating
diameter in eights of an inch. “T-5” indicates a lamp of 5/8”
diameter; “T8” means the lamp diameter is 8/8ths or 1”; a T12 means 12/8ths or
1.5” inches in diameter. This may be followed by ballast
requirements such as “HO” or “VHO.” Lamp Kelvin Temperature may be
noted as 30 (or 3,000K), 65 (6,500K) and so on. Osram/Sylvania lamps
often have “D8” immediately preceding the color rating.
Example: URI FR30 T12
URI is the manufacturer; FR
designates this lamp as “Fluorescent”, 30 = 30 watts, T12 designates =12/8ths,
or 1.5” diameter.
A spectrometer (Ocean Optics, model
USB-2000, Dunedin, Florida) was used to evaluate sunlight and individual lamp
spectral qualities. Data was down-loaded from the spectrometer into MS
Excel worksheet, and analyzed with a proprietary program. Light
transmission data of Jerlov (1976) was used to estimate spectral qualities of
sunlight in Oceanic Type I seawater at depths of 1 meter and 10 meters.
The results of testing of URI
Actinic White and Super Actinic were combined by simple addition.
Figures 1 – 23 demonstrate spectral
qualities of sunlight (surface and at-depth values) as well as lamp spectral
qualities of various fluorescent lamps. Click on any diagram to open a
window with a full size image.
Figures 1 and 2: Sunlight at noon.
Figures 3, 4 and 5: Comparisons of
Sunlight (Surface, 1 Meter and 10 Meters).
Figures 6 and 7: URI Super Actinic
Lamp Spectral Quality.
Figures 8 and 9: URI Actinic White
Lamp Spectral Quality.
Figures 10 and 11: URI Lamps “Super Actinic” and “Actinic
White” Combination Spectral Qualities
Figures 12 and 13: Spectral Qualities of Helios T-5 Actinic Lamp
Figures 14 and 15: Spectral Qualities
of ATI T-5 “Actinic Blue” Lamp
Figures 16 and 17: Spectral Qualities of ATI T-5 “Aqua Blue”
Figures 18 and 19: Spectral Qualities of Narvia T-5 “Biolight”
Figures 20 and 21: Spectral Qualities
of ATI T-5 “Blue” Lamp
Figures 22 and 23: Spectral Qualities of GE “Warm White” Lamp
Two lamps – the Narvia Biolight and
URI Actinic White – offer reasonable approximations of sunlight spectral
quality. If an aquarium is especially deep (say, over 76 cm in
depth), aquarium water with low APHA Color (“yellowness”) will naturally and
selectively ‘filter’ light from these lamps and offer reasonably realistic
representations of very shallow waters.
The ATI ‘Aqua Blue’ lamp offers a
reasonable rendition of 10 m deep oceanic water – which brings up the question –
do we really wish to replicate the ‘blueness’ of deeper waters? Certainly, this
is a personal choice, but I suspect that an aquarium illuminated by only ‘blue’
lamps will be the choice of few hobbyists. I tend to think that the majority of
reef-keepers would prefer a ‘warmer’ look, one where color rendition is accented
by the yellow, orange and red wavelengths of low-Kelvin fluorescent lamps.
The question is not if we can
imitate light-at-depth, but if we actually want to. Unless the goal is to
illustrate coral host tissue fluorescence through excitation with a predominance
of violet/blue wavelengths, I suspect most display aquaria would be unnaturally
‘warm’ in appearance due to yellow-red wavelength generation by the majority of
Discussion of spectral quality would
be incomplete without at least a mention of light intensity. Figure
24 demonstrates PAR values at various depths of oceanic water (estimated to be
Jerlov Oceanic Type I) off the west coast of the Big Island of Hawaii.
These measurements were taken at noon on a cloudless day, when water
transparency (visibility) was excellent (easily exceeding 100 feet). Many
fluorescent lamps are available in ‘high’ and ‘very high’ outputs; T-5 lamps
offer the advantage of small diameter, thus allowing a greater number of lamps
within a given area (this also allows custom spectral quality through selective
combination of lamps).
Reproducing natural light intensity
is possible, but not probable, with fluorescent lamps. As one can see from
Figure 23, light intensity is ~1,500 µmol·m2·sec (~75,000 lux) at a depth of 1
meter, and ~750 µmol·m2·sec (~37,500 lux) at 10 meters.
If replication of natural light
intensity is impractical (in many cases), then one has to wonder why episodes of
coral bleaching are noted under conditions of low-light intensity and natural
temperatures. The answer seems to be linked with spectral quality, and
associated imbalances of energy transfer between photosystems. This should
be investigated further. Of course, it is also apparent that light
intensity plays an important role in photo-bleaching, and we perhaps we should
establish acceptable light intensities at various red-to-blue ratios. This, too,
bears more investigative work.
Many thanks to Perry Jones of
Sunlight Supply for supplying some of the fluorescent lamps.
I.E.S. Lighting Handbook, 1984.
Illum. Eng. Society, New York.
Jerlov, N., 1976. Marine
Optics. Elsevier Oceanography Series, Elsevier Sci. Publ. Co., New
York. 231 pp.