Lighting for underwater videography has never been higher performing nor such good value as it is today thanks to battery technology that can pack a lot of power into a small space resulting in good burn-times per charge and the ability to fire up high output light sources. At the same time LED technology has progressed to make the most of this.
A word about lumens. Every manufacturer rates their light by the lumens they output. However, a 1000 lumen light with a narrow parabolic reflector will punch its way through the water so that more light arrives at the subject. This light is measured in LUX. Alas, video demands even lighting. Otherwise you’ll get a very patchy result. The more lumens you start with the better you results will be.
You can get lights that accomplish the same output in lumens but in different ways. Some use a cluster of small LEDs while the better ones use a single large LED. Why do I say ‘better’? Well, it’s about the quality of the light. A cluster of LEDs will provide a cluster of shadows when close to the subject and although this might not offend the eye when looking directly, it can tend to give the image a degraded unsharp appearance.
So what if you set the light further from the subject? You’ll appreciate that nothing is brighter than the sun yet the colour of its light is degraded once it has passed through only a few metres of water. That‘s because water absorbs light selectively. The longer wavelengths from the spectrum, the reds and greens are quickly soaked up by the water, leaving only the blue light to penetrate very far. That’s why unlit video looks blue once you get very far from the surface.
The same thing happens with a video light. You’ll notice that as you get closer to your subject with your camera and lights, the subject does not simply become brighter, it becomes more colourful. Even the most powerful video light has a problem penetrating much more than a metre of water, once it is competing with daylight filtered blue from the water above. Strangely enough, it’s in daylight that you need more lumens and it’s for this very reason.
At night or inside a dark wreck or cave you’ll find the less powerful lamps are just as effective. It takes a very bright light indeed to light up a reef in daylight and you will still need to get as close as possible and use a fisheye lens to restore the full width of subject.
So my advice is to get the lights with the greatest output possible from a single LED with a wide beam reflector. Why do I speak in plural? Well, with video you need an even light over the subject so two lamps of half the output in lumens will be superior in effect to one lamp of twice that.
There’s then the question of the colour of the light. This used to be described in °Kelvin. The higher the temperature the more blue the light. Daylight on a sunny day with puffy white clouds is around 5500°K so that’s a good light source colour temperature to aim for. There’s also the Ra rating. The manufacturers of more sophisticated light will provide this in their specifications. This reflects the color rendering index of a light source and determines the spectrum of the light produced. Like fluorescent tubes, some LEDs are missing part of the full spectrum and thereby give some less than satisfactory colour rendering, depending on the colour of the subject matter. However, since what you will be recording is underwater and rarely seen by natural light, who’s to judge what’s right?
A word about flying with lithium batteries: To determine whether you can carry your lithium batteries on board a plane requires your close inspection of the batteries. It depends on their configuration and either Watt/Hour (Wh) rating for rechargeable batteries or Lithium Content (LC) for non-rechargeable batteries. To convert Amp/hours (Ah) to Wh, multiply the marked Ah rating by the rated voltage of the battery. (There are 1000 mAh in 1 Ah.)
Less than 100Wh or 2G (LC) batteries contained in equipment can be carried on or stowed in your checked baggage. Typically, the AA batteries commonly used in much photographic equipment fall into this category. However, you must carry spare batteries with you, not checked in.
Laptops usually have 11.1v batteries while mobile phones use 3.7v. More than 100Wh but less than 160 Wh batteries can be carried on or checked if installed within a laptop, camera or mobile phone, but you must carry on your spares (a maximum of two). However, you should get operator approval for the spares from check-in staff. If you have a video or powerful dive light, check the size of the batteries if they are lithium. They will be marked with Ah/voltage or Wh. Batteries of more than 160 Wh can only be presented to check-in staff and packed in your checked luggage in accordance with IATA Dangerous Goods Regulations. Generally, large lithium battery packs such as used in DPVs are barred from air transport. If you want to transport such a DPV by air, check that its battery pack is ni-cad.
If you carry on spare batteries, their terminals must be protected from short-circuiting by either enclosing them in their original packaging, taping over the terminals, or carrying each battery in a separate plastic bag. Batteries in the mobile phones, laptops, etc., that you check must be switched off and measures taken, if necessary, to ensure they cannot be accidentally activated. More info: www.iata.org/whatwedo/cargo/dgr/Pages/index.aspx