Lighting is often touted as one of the key components of a successful Reef but with so many types and brands each with different models it can get confusing pretty quickly. This blog will talk go through the main types of lighting and the differences between them so that you can make a more informed choice when it comes to choosing the right light for you.
So, let's start with a bit of context about lighting our marine aquarium, why is marine aquarium lighting so important? Simply put, we're trying to replicate what the fish, critters and corals experience in their natural habitat. Most often this is an ecosystem somewhere near the equator or tropics where the sun is at its strongest. Therefore the light which they are used to compared to us in the northern hemisphere is significantly more intense, plus the Great Barrier Reef doesn't have as many cloudy, overcast miserable days as we do! So intensity is the first part of the lighting equation, the second is spectrum. If we dig out our old school science books we'll see that light is in fact electromagnetic radiation of varying wavelengths. The human eye can perceive wavelengths of light between 400-700 nanometres which makes up the colours we see around us. Light that we can see therefore in its simplest definition is a blend of different wavelengths (or simpler yet; colours). Light allows us to see but for photosynthetic organisms that rely on it for energy and the different wavelengths suddenly become very important. This is because photosynthetic organisms have evolved to absorb light of certain wavelengths in order to generate energy (to photosynthesise). Ergo, corals and algae have evolved to absorb certain wavelengths of light in certain measures or 'blend' in order to meet their photosynthetic requirements. We, as the plucky aquarist, try to supply the correct wavelengths of light in the correct measures in order to meet these requirements in the form of aquarium lighting. The 'blend' of light that corals need isn't limited to the spectrum that we can see, it also includes wavelengths that we cannot such as Ultra Violet, which makes the issue of getting the 'right light' just that little bit harder. The importance of lighting isn't just limited to corals and algae however, it's also important for fish. Whilst they're not photosynthetic, lighting will still help regulate growth, hormone production, pigments and can help boost the fish' immune system so whilst there is a difference in the importance of lighting for say a SPS dominated reef tank, it's certainly not true that lighting isn't important to fish only systems.
That's the context to why lighting is important, let's have a look at the main types of lighting for a marine aquarium and some quick pros and cons for each.
Metal Halide.
Metal Halide lighting comprises of a bulb and a lighting unit to house the bulb. In principle, it is similar to the typical light bulb you would have in your house (before LED bulbs). The difference between the light bulb in your house and a metal halide bulb is the composition of the gas within the bulb which electricity is passed through in order to produce light. Metal Halides have a mixture of Mercury and Metal Halide Gases (hence the name Metal Halide). This produces a strong and high quality light which is often used in industrial settings such as lighting sports pitches and warehouses (although LED is taking over). Metal Halide was once the be all and end all for reef keepers, especially those keeping SPS due to the high quality/spectrum of light and its ability to penetrate deep into the water. It has a number of drawbacks though such as; warm up time (when the light is switched on the bulb needs time to warm up before it emits its full light potential), they can't really be dimmed, they can be noisy, give off a lot of heat and the bulbs will require replacing over time.
Metal Halides, although old tech are still hailed as one of the best lighting options out there by a lot of reefers, specifically for SPS. They are still available to buy and are used by some but are generally less common than they used to be. Advances in LED technology have also closed the gap and now offset a lot of the drawbacks that bulbs present (more on LED later) which has drawn some reefers away from bulbs.
T5.
T5 lighting is a form of fluorescent light tube similar to fluorescent lighting you may have at home (often kitchen lights) or have seen in office/public buildings. The difference between T5 specifically and general fluorescent tubes is that they are more efficient, emit more light and are slightly smaller in diameter than standard bulbs. They require a specific T5 ballast (mounting sockets and brackets essentially) in order to use. These can come as standalone ballast which look quite industrial and simplistic but are intended to fit inside aquarium hoods/lids whereas the T5 fixtures are designed to be an all in one unit separate from the aquarium and as such are a bit easier on the eye. T5s are often cited as producing a flat blanket of light which covers the aquarium and minimises the amount of shadowing. This is largely due to the fact that the bulbs are long and the light they emit is omni-directional rather than focussed beams of light. If you do choose to use T5 you will need a few of them across the aquarium in order to get the total spread of light needed. This opens up the opportunity though to have a mix of bulbs. The most common mix is to have whites and blues in order to get a good spectrum of light to grow coral whilst making your aquarium look good to the eye.
T5 bulbs will still need replacing periodically when the tubes burn out and new bulbs will need burning in before use. They are slightly more efficient than Metal Halides, bulbs are cheaper and they give off less heat but they are also criticised for not having the 'punch' into deeper aquariums that Metal Halides do. That all being said, T5s are a popular option for many reefers still who argue that LEDs don't have the spread and spectrum that bulbs do although as I alluded to earlier, advancements in LED technology means this gap is closing quickly.
LED.
LED is the newcomer to the lighting market when compared to the OG Metal Halide and T5 setups however it is fast becoming the most popular option for lighting aquariums. LED stands for Light Emitting Diode which is exactly what these lights are, small diodes which emit strong beams of light. There are two immediate drawbacks here which are that diodes only emit one colour of light which makes achieving the correct spectrum of light into the aquarium difficult and the second is the beams of light are extremely narrow and focussed which means that the intensity is really strong over a small area. This can result in 'hotspots' where light is extremely strong and can damage coral and algae. LED lighting manufacturers have worked hard to overcome these issues however and now pretty much all fixtures on offer will house a blend of coloured diodes to create what each manufacturer believes to be the best spectrum. In fact some fixtures such as the AI Hydra and EcoTech Radion give you the option to control each coloured diode's intensity to create a custom spectrum and overall intensity of light. The second issue is the focussed beam of light. Manufacturers are overcoming this by incorporating a means of blending the light from each diode as it leaves the light fixture. The main way they do this is with a frosted glass cover over the LEDs such as what Phillips Coral Care have developed and what the most recent Radions are doing. This 'blending' to create a complete spectrum of light rather than individual colours being beamed into the tank individually is what has arguably really closed the gap between LED and bulbs. The real benefits to LED that should be mentioned are that they are more efficient, give off less heat, the diodes will last in some cases 50k plus hours as opposed to T5s max 12 month lifespan, and finally they are much more controllable with the option to create custom settings and the ability to gradually dim the lights in the morning and evening (ramping up and ramping down) with deep blue light to make corals 'pop'.
Hybrid.
Hybrid lighting isn't a unique type of lighting per se but rather a mix of two types put together to get the benefits of both. So really this is a 'method' of lighting rather than a specific 'type'... if I'm being pedantic. But anyway I think it's worth mentioning in this blog. Hybrid lighting consists of LEDs and bulbs or tubes, either Metal Halide or more often than not, T5. Some reefers construct their own brackets to retrofit these lights together which can also make use of LED strips like the Reef Factory Flare Bar which is designed to be an add on or they use specifically designed lighting units which house both bulbs and LEDs. The perks of hybrid lighting is that you get the coverage and spectrum from the bulbs whilst you get the 'pop' from LEDs which bring out the fluorescence of the corals. You still have the drawback of bulbs needing replacing and burning in etc however and more lighting units will add to the overall power consumption but this option is a viable option used by reefers primarily growing coral, more often SPS.
As for advice on what lighting system is best, well, this is where it gets tricky and the topic certainly deserves a much more in-depth blog of its' own. If you're running a fish only system then my advice would be to go for some marine aquarium specific LEDs, whichever suits your budget and fits your aesthetic for your aquarium. They're power efficient and they won't need replacing nearly as often as what bulbs will. If you're looking to keep coral then it gets extremely tricky and needs a blog post of its own. What I will say though is this is what is running over the shop systems; SPS tray - Phillips Coral Care Gen 1 and Gen 2. LPS Trays - Coral Care again, Kessil and recently Reef Factory Flare Pro. Soft Coral Trays - Kessil and Coral Care.
I hope that sheds some light on reef lighting.... I know, I know it's a terrible dad joke! But I do hope it has helped and all I can say is welcome to the discussion on reef lighting because if one thing is for certain about reefing; there will always be a debate on which is best!