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Aquarium Luminaires

Apart from length, what are the other dimensions for the Overtank Luminare?

Every Arcadia Overtank Luminaire has the same profile, with just the length changing.
This is 6cm deep and 24.5cm wide.
When correctly mounted, the base of the Luminaire is raised 7cm above the glass rim of the aquarium, when positioned with the hood down.
The length of the Overtank Luminare bracket is 23.5cm.

Can I upgrade my 150Watt pendant to a 250Watt model?

No - the bulbs are physically very different in size, and so require different lampholders for them to fit into.
Not, only that, but the electronic components used to power the 150W versions are not the same as those used to power the 250W versions. Basically, the entire internal workings would need to be altered.
The only parts common to the two models are the outer body and the cover glass.
Once the unit had been returned and altered, the cost of the parts and labour involved would be no saving on purchasing a new 250W unit.
For this reason, it is important when purchasing a pendant, to take the time to decide which model is correct for you.

Can a Metal Halide pendant be mounted within a cabinet style aquarium hood?

Metal Halide lamps, and in particular higher wattage halide lamps, produce a lot of heat. If this heat is unable to escape the thermal cut off device will trigger, a saftey mechanism which will switch the lights off to protect the pendant from over-heating.

It is therefore essential that all metal halide systems are mounted in such a way that allows the correct level of ventilation, which rules out the oprion of enclosing them within an aquarium hood.

How far can I adjust the legs on the Overtank Luminaire?

The legs (mounting brackets), of the Overtank Luminaire have been designed to connect via a sliding pivot. This gives additional flexibility when setting up the Overtank Luminaire. These "legs" can alide outwards to fit an aquarium which is 5cm longer than the length of the Luminaire.

I have a T8 model of the Overtank Luminaire - can this be upgraded to a T5 model?

Sorry but the answer in this case is no. Almost all of the circuitry is different between the T5 and T8 versions, the only common part if the outer shell.

If I use a pendant over my freshwater tank, can I change it to suit marines at a later date?

Yes - the freshwater version of the 'Series 3' uses 5,200K lamps and 'Original Tropical' fluorescent tubes, whereas the marine version uses 14,000K lamps and 'Actinic Blue' tubes.
To change a pendant from freshwater to marine (or vice versa), it is simply a case of purchasing the required lamps/tubes and swapping them over - all other components of the pendant are identical.

Is the new ARC POD(TM) suitable for use with a marine aquarium?

The ARC POD comes complete with the new Arcadia Original Tropical Compact Lamp. This lamp has been developed for freshwater use and therefore is not ideal for general marine use. However, the ARC POD(TM) is ideal for use over a marine Refugium, as the Original Tropical compact lamp is ideal for promoting plant growth.

The largest Overtank Luminaire is 150cm. However, I would like to use one over a slightly larger tank, do you have any suggestions?

There are two possible solutions to your problem:-

1) To attach, using an aquarium silicon sealant, some suitably strong bars across the width of the tank. Ensuring that these bars are placed at suitable frequencies for the 150cm unit to mount on and then mount the Overtank Luminaire onto the bars rather than directly onto the aquarium ruim.

2) Alternatively, suspend the 150cm Overtank Luminaire from the ceiling, using the Overtank Luminaire Suspension kit, which can be ordered from all good retailers.
What are the different types of fluorescent lamps?

Linear lamps are the most common, and come in several widths.

The most common European width is now the 1” lamp, which is 26mm, but it is also known as a T8 lamp. Each “T” represents an eighth of an inch, therefore 8 x 1/8 = 1”.

The old style of linear lamp was the 1 1/2” lamp, or T12 lamp, which is 38mm in the EU.

Short lengths are sometimes 5/8” (16mm) in width, known as T5 lamps. Recently, T5 lamps have become available in longer lengths too; these need electronic ballasts to run, and produce some 50% more light per linear length than standard T8 lamps.

Special applications can use either T1 or T2 lamps, but their application is rare.


The wavelengths (colour) radiated by the phosphors vary with the chemicals used. Old lamp technology uses halo-phosphates, which contain calcium, antimony, chlorine, fluorine and manganese. With no manganese the colour of the lamp is blue and by adding different amounts of manganese, blue-white and white to yellow-white lamps are obtained. Halo-phosphates output light fairly evenly over the visible spectrum.

New technology lamps are known as tri-phosphors. The phosphors used are selected to produce high-energy spectral band emission at the 3 critical frequencies which correspond to the red, green and blue of our eye’s perception. Thus, the light emitted appears far brighter than a halo phosphate lamp.

Tri-phosphors are made with a combination of expensive rare earth elements. There are 30 such elements, all found in group 3 of the periodic table, and the 6th and 7th periods.

By mixing the different elements available, it is possible to tailor make the SPD (“spectral distribution”) and the colour temperature of the lamp.

Lamps without phosphors emit ultra violet, including dangerous UVC, and are known as germicidal lamps. They are usually made with a more expensive quartz glass, so that the UV is transmitted through it.

Compact Lamps

The arc formed within a fluorescent lamp does not have to travel in a straight line. Thus, non linear lamps can be manufactured. The early versions of these were circular lamps, but later, compact lamps were manufactured. These come in a variety of forms, and nearly all of then require an electronic ballast to operate. In many household compact fluorescent lamps, the ballast is built into the lamp base.

These lamps run cooler than conventional linear lamps, and are more energy efficient.

A compact lamp of 20W has the equivalent light output of a 100W incandescent lamp, for example. That’s because most of the energy from an incandescent lamp is wasted in heat.

One must be very careful in specifying an electronic ballast for a compact lamp. An electronic ballast for a linear T8 lamp will not run an 18W compact lamp.

A further area of difficulty is with the lampholder. There are several different lamp holders for compact fluorescent lamps, each requiring a different lamp holder.

Compact lamps are sometimes referred to as PL or PLL lamps, which are all “2 finger” lamps. The PL designation refers to lamps of 5, 7, 9 and 11 watts. The PLL designation refers to lamps of 18W or more, namely 24, 36, 40, 55 and 96 watts. The term PLC, refers to cluster lamps, which have more than 2 fingers.

Reflector lamps

Some lamps, such as sun bed lamps, have an internal reflector to direct light to where it should be. Efficiency is thus improved.

The extreme reflector lamp is the aperture lamp. Where only a narrow slit is available for the light to exit. These specialist lamps are used for edge lit signs.

What colours are available for the Overtank Luminaire?

Any, just as long as it is Silver!

Fluorescent Lamp Reflectors

Can I use a standard Reflector with a T5 lamp?

In theory, yes a standard reflector can be used on a T5 lamp. However, Arcadia recommends that the T5 reflector is ideally used with the T5 lamp as the profile is closer.

Does a reflector really make much difference?

A fluorescent tube is circular in cross-section, with light rays being emitted equally from all points of that circle.
Rays coming from the bottom half, illuminate the water as desired, but any rays coming from the top of the tube hit the inside of the aquarium hood and are wasted.
If a reflector is placed above the tube, these rays are bounced back towards the water, and so 100% of the tubes output is being directed where you want it - into the tank.

Fluorescent Lamps

Do I have to use the specific wattage controller with my lamp?

Yes, using an existing controller with a new wattage of lamp is not a good idea. If the controller is a lower wattage than the lamp then the lamp may fail to light, or could result in a lamp with a weakened output. Using a controller which is a more powerful wattage than a lamp will mean either a shorter life-span for the controller - as it has to work very hard to light the lamp; and could result in the lamps being destroyed and having to be repalced at frequent intervals.

How do I choose which lamp is for me?

Details of lamps in the range with their fitting types are are available for download from here.
Alternativley you can contact our Sales and Customer Services Department. See below:
Tel: +44 (0)1737 72 3838
Fax: +44 (0)1737 72 3815

Is it recommended to use more than one fluorescent tube?

Unfortunately, many modern hoods do not have the capacity for more than one tube, but for those that do there are definite benefits.
Using more than one tube increases light intensity, and further encourages plant growth.
Also, different and pleasing effects can be created by combining tubes of different outputs such as the 'Original Tropical Lamp' and the 'Freshwater Lamp'.
In the case of a marine reef tank lit by tubes, then a single tube such as the 'Marine White' is definitely not enough, as an Actinic Blue tube should be used in conjunction - If desired, this can be left on, on its own to create a moonlight effect.

When is the best time to fit a new lamp?

The Arcadia Ultra Clear UVC lamps have a much longer life-span than most other brands and can be used for a period of 12 months. To get the optimum performance from the lamps, they need to be operating at maximum strength in the spring and summer months when the algae problems are at their worst.
Therefore, we recommend that at the start of each season a new lamp is fitted so that the output is at the strongest level.

Why do the screw caps stick to the fluorescent tubes?

There are two causes for this:

The first is when new, the IP67 special sealing ring is more rigid when used for the first time. By administering a small amount of Vaseline (non petroleum based) or silicon grease will assist the ring in sliding over the tube more freely. This will also allow for easier ongoing maintenance.

The second is due to heat dissipation from both types of fluorescent tubes used (T5/T8) and the special IP67 tight sealing mechanism, (designed to prevent water ingress) this can lead to the sealing ring sticking to the tube over a period of time used. To prevent the long term damage of the IP67 sealing ring we recommend lubricating the ring with a small amount of Vaseline (non petroleum based) or silicon grease at the initial installation to enable easier maintenance to be carried out when replacing lamps.

Screw cap replacements are available at the online spares store.

Metal Halide Lamps

How do I maximise the benefit of the HQI lamps themselves?

When using the Arcadia 14,000Kelvin lamp in a 4 Series pendant, the light output is being maximised by a specially designed reflector which focuses the light into the aquarium.
The fluorescent Marine blue actinic tubes that are fitted into the pendant, supplement the HQI lamp by enhancing the natural fluorescence possessed by many invertebrates, and also give the option of dawn/dusk periods.

Why should I use a Metal Halide lamp?

Metal Halide is commonly accepted as the best substitute for nature when it comes to aquarium lighting, particularly for marine-life aquariums.
The exceptionally high light output when compared to other lamp types such as fluorescent tubes, makes them a very effective light source, particularly for the larger tank set-up.

Magnetic Controllers / Electronic Controllers

Do I have to use the specific wattage controller with my lamp?

Yes, using an existing controller with a new wattage of lamp is not a good idea. If the controller is a lower wattage than the lamp then the lamp may fail to light, or could result in a lamp with a weakened output. Using a controller which is a more powerful wattage than a lamp will mean either a shorter life-span for the controller - as it has to work very hard to light the lamp; and could result in the lamps being destroyed and having to be repalced at frequent intervals.

Do you manufacture an 80W Double model of the Electronic Controller?

No. We currently produce a single lamp model for this wattage electronic controller. The reason for this is that we have been unable to source a twin electronic ballast that satisfies our high standards and provides the quality of product you would expect from us.

I see that a Twin model controller is available for 24W or 39W models. Can two different sizes of lamps be used on the same controller?

The simple answer is no. The double models of the Electronic Controllers need to run 2 lamps of the same wattage at the same time. Mixing lamps of different wattages will result in the lamps failing to light and could also be potentially dangerous.

Why is the mains lead of the ULTRA SEAL(R) Controller so Short?

New legislation has been introduced to protect the Aquarist. Therefore Arcadia have redesigned the popular Controllers and replacement lead sets to comply with the need to improve on safety. Therefore the mains lamp lead has been reduced to 50cm. However, we have responded to the request from many of our customers to increase our lamp holder leads to allow the Aquarist greater flexibility to position the lamps exactly where they want them.


How does a fluorescent starter switch work?

Firstly, why is a starter switch required?

Inside a fluorescent lamp, there is an arc of electrical current running from one cathode at the end of the lamp to the other. This arc needs some encouragement to form in the first place, and this is where the starter switch is required. The cathodes of the fluorescent lamp need pre-heating before this arc can be formed. The fluorescent starter switch is effectively a time delay switch, enabling this to happen.
Without a starter switch, the lamp will just flicker, and a continuous arc with not form
Electronic ballasts have the starter function built into their circuitry.

In principle how does it work?

When you turn on a fluorescent lamp, the starter switch ensures that the current flows through the ballast and through the cathodes of the lamp, but there is no arc formed through the lamp.

The cathodes at the ends of the lamp are heated by electricity, the molecules in the cathode become excited, and electrons are liberated into the lamp. The starter switch then opens, forcing the current to form an electrical arc in the lamp, causing the lamp to light.

In practice how does it work?

Inside the starter switch canister, there is a bimetallic strip, which is contained within a small glass envelope containing argon gas. This is a strip of metal made of two different types of metal, each having a different rate of expansion. Thus, when heated, the strip bends.

When the current is first switched on, the bimetallic strip is straight, and its contact open, so the current going through the starter switch goes though the argon gas in the form of an arc. The current is only flowing through the fluorescent lamp cathodes at this point. The argon gas heats up, causing the bimetallic strip to bend towards the other contact of the starter until the two contacts close. The argon arc no longer operates and as the source of the heat is removed the bimetallic strip cools and begins to straighten until the contacts open again.

The opening of the contacts forces the current to form an electrical arc in the lamp, causing the lamp to light. As the current flow is now through the lamp, the starter switch is effectively left out of the circuit, as there is no longer enough voltage available to cause another arc in the argon within the starter switch.

Lamps used in conjunction with starter switches, are sometimes called pre-heat lamps, due to the need for their cathodes to be preheated.

I have purchased an I-Bar. Why are the lamps not central?

For some of the T5 versions of the I-Bar we have staggered lamps on both sides of the product. The reason for this is that currently the range of tube sizes available for T5 lighting is not very large, but we produce I-Bars to fit a wide variety of aquariums. In some cases even the largest T5 lamps is not long enough for the relevant T5 I-Bar. Rather than mounting them centrally, which would result in dark ends of the tank, we have staggered the lamps to give the best possible light spread.

What fluorescent lighting do you recommend for a cichlid aquarium?

If your cichlids are south American (e.g. apistogramma or keyholes) or central American (e.g. Cichlasoma nicaraguense, or C. panamense), or if they are west Africans (e.g. Juwel Cichlids or Kribensis), then you should follow recommendations as for other freshwater aquariums - in other words , the freshwater lamp to highlight colours, coupled with an original tropical lamp if it is a tank containing plants ( not always possible with cichlids!)

If however your tank is one containing African rift valley cichlids, such as those from Lake Malawi, then a good alternative is to use the Marine white lamp.
Although these cichlids are not marine, the bright colours of fish such as Labidochromis, Haplochromis, or Tropheus do stand out well against the intense white provided when you use the marine white lamp.
It would not be necessary to use the Actinic blue lamp as it would in a marine reef aquarium (although it could still be used to create a moonlight effect if that was desired). Alternatively, if you have the facilities for multiple tubes, then you could use more of the marine white - this would certainly be beneficial for any algae grazing mbuna, as it would increase the availability of their favourite food.

What does it mean when people refer to warm and cold lighting?

This is with reference to the Correlated Colour Temperature (CCT). To enable a general understanding of what type of light a lighting system produces, the colour temperature of the light produced from standard types of lighting is used to provide guidance. ie people know what a candle, incandescent bulb and a summers daylight, light looks like. So these are used as reference guidance for describing units unseen by all.

The spectrum diagrams below the lighting types above show the high levels of reds and oranges in the warm light spectrum (3200K) and the change to high blues and no reds/oranges in the cooler lighting spectrums ( 5,600K).

What does it mean by the colour temperature?

This relates to the use of the” black body iron radiator” or an “iron bar” source heated to produce the same level of light colour. Imagine a blacksmith heating up an iron bar in a furnace and watching the iron bar changing colour. This change in colour was used to determine whether the iron bar was ready to be worked for the results required. This method is used to try and standardise lighting characteristics. The colour the metal changes happens at different temperatures and is measured in Kelvin (K).

Low colour temperatures (yellows, oranges and reds) 2500-3000K (warm)are at one end of the scale while high colour temperatures (blues and greens) 6000- 20000K (cool) are at the other end.

What does the CRI or Colour Rendering Index mean?

The Colour Rendering Index (CRI) scores match the lighting of a set of test colours. The main reason to do this is to score different types of artificial lighting methods to provide a universal standard of testing their light produced in a bid to replicate the lighting levels of the sun. The CRI of the sun is 100. So the idea is that the closer the lighting is to this number, the closer it replicates natural sunlight. The scale used for this purpose is 0-100.

There are two main types of test colours used, one is the basic (R8) test colours which have eight different colours and the extended R9 range of test colours which add another 6 colours to the original 8 making 14 test colours.

Why should I care what light I use for my aquarium?

As more and more scientific information becomes available from universities and scientific research it is soon apparent that lighting has a big impact on the inhabitants life.

Some species have specialised lighting requirements or levels for optimum environment factors. The correct lighting levels and lighting regime can provide increased immunity, less stress and optimum breeding requirements for fish.

Arcadia have spent over 40 years specialising Arcadia lighting systems for the inhabitants of your aquariums.

What should I look for in an aquarium light

You should ensure that the light conforms to the current European Safety regulations and possesses the relevant symbols to state so. Ideally the unit should be Ingress Protection (IP) rated. The highest level is IP68 which means it is submersible.

Next is IP67 which means it is waterproof and although it is not submersible it has been tested to being temporarily submersed for 30 mins in water. This will only be relevant to part that is IP67 tested, not the whole luminaire.

IP64 is generally accepted as a splash proof requirement and out of the three mentioned is the lowest level of safety protection for a luminaire. (By suspending the luminaire from a suspension kit, a reduced level of safety requirements are required to be met. Thank if the unit was to be fitted to the aquarium.)

Should I get electrical shocks from my lighting unit?

No, you should not get electrical shocks from a correctly performing lighting unit. If you do it may be due to a fault on the lighting unit. It may also indicate poor earthing, an electrical fault, salt creep shorting or questionable insulation of the electrical wiring to the unit. Always fit a Residual Circuit Breaker (RCB) to your aquarium mains supply. This will ensure your safety, as if it is a faulty lighting unit, it will trip the mains supply before drawing too much current.

What is an LED?

An LED, or Light Emitting Diode to use its full name, is an electronic component known as semiconductor or Diode. When it is working it conducts electricity and emits light. There are many symbols used to represent an LED.

Image 1 Image 2: OSRAM LED Lighting products Image 3

The LED is made of material that is doped with other material types to provide what is called a p-n junction, and when electricity is supplied to the anode (P-side of the junction), the diode will conduct a current through the material to the cathode (N-side) of the junction and emit energy at a visible light wavelength that is related to the energy dropped across that junction. It will only allow current to flow in one direction it will not flow in reverse ie cathode to anode. The colour of light emitted is related to the drop of energy across this junction and the type of material used to make the diode.

What is Haitz law?

Haitz’s Law states that, every decade the cost per lumen will fall by a factor of 10 while the output per LED package increases by a factor of 20.

What is PAR and PUR?

PAR stands for Photosynthetically Active Radiation.

PAR is a measurement used to determine the strength of the visible lighting spectrum 400 - 700nm that is available to be used for photosynthesis, by plants and most marine corals. It is measured in microeinsteins per second per square meter (μE/m2/sec)

PUR stands for Photosynthetically Useable Radiation.

PUR is the specific part of the lighting spectrum that is used by the organism in question. This may be within the blue part of the lighting spectrum or the red part of the lighting spectrum or both but it will be required by the organism to create photosynthesis.

Pond Lighting – UVC Fluoresecent Lamps

If the ULTRA CLEAR UVC lamp is used over an aquarium, will it control algae?

The ULTRA CLEAR UVC lamps emit high levels of UVC light. They must NEVER be used in an aquarium system as an alternative lamp. These lamps are potentially very dangerous and must be enclosed within light-sealed units - such as pond clarifiers in order to avoid exposure.

The lamps should never been looked at directly as this can cause serious and painful damage to the eye. In addition UVC is the Ultra violet light that can create severe burning on the skin and could result in skin cancer.

All Arcadia UVC lamps are clearly packed to avoid any confusion.

These lamps also appear see-through and are unlike the rest of the Arcadia lamp range.

If in doubt, consult your retailer.

Is the use of a UV lamp harmful to reptiles and birds?

UV light is comprised of UVA/UVB and UVC. In nature, the ozone layer acts as a filter to the UVC spectrum of light. If we did not have this protective layer then we would be exposed to burning rays of the sun. UVC lamps are designed to kill off algae and therefore are dangerous to all living organisms. UVA and UVB, however are required by certain species - in the aquarium for the photosythesis of plants and the development of coral, for example. Reptiles and birds need both UVA and to some extent UVB in order to see things clearly and in some species for the healthy development of bones to prevent ill-health and soft bones. For example some species of reptiles are unable to synthesise UVB through their diet and are therefore reliant on receiving this from light. If the reptile is kept out of sunlight they will require a specially developed UVB lamp in order to produce Vitamin D3 which they require to make their bones strong. Without this vitamin the reptiles would develop bone problems and ill-heath which would eventually lead to their early demise.