Light & Colour: underwater lights.
Anyone who's done even a little underwater photography will know that light and colour are inextricably linked. As soon as you go underwater, even when close to the surface, you'll start to lose colour as you start to lose light.
Reds will start to be lost at around 5m, oranges at around 7.5m, yellows at 10-15m and finally greens at around 20-25m.
These colours can be difficult (or impossible) to post-edit back into your images, which is why we're always recommending adding addtional lighting with strobes and LEDs - light, light and more light! To quote the sage advice of Dave Moran: "You can never have too much light."
But not all light is created equal. In addition to colour temperature, measured in kelvins, there is also CRI, or Colour Rendering Index. These are two different ways to talk about different aspects of light which can both affect the colours you'll see in your finished image.
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Kelvins & Colour Temperature.
Kelvins will usually be represented on a scale from around 1000 to around 12000 K. The lower end of this scale represents light quality more similar to a candle, while the higher ends will be more similar to blue sky. You'll be familiar with this kind of scale if you've bought lightbulbs, where this quality is usually represented by language like "warm light" and "cool light".
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Warmer lights, ie., towards the lower end of the scale, may produce a very slight yellowing of your subjects under some conditions, while cool lights may produce a more blue light (which is obviously already an issue for divers). Typically light around the middle of this scale is preferred for underwater photography.
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Even when shooting near the surface, it's important to note that the amount of light that penetrates the surface depends on surface conditions, the weather, and the time of day. Choppy waters reflect more light than calm waters. Sunlight from the horizon is reflected much more than sunlight from straight above.
So the brightest conditions underwater will occur on a sunny day, with a calm surface between 10am and 2pm. Light penetrating the surface early in the morning and late in the day has a soft quality and can be great light for underwater photography - it just depends what you're trying to achieve!
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Colour Rendering Index or CRI.
CRI has been the lesser understood cousin of light quality for some time. Perhaps for this reason, many dive lights don't actually give you this information. But for those that do (Keldan, i-divesite), here's how it works.
The CRI of a bulb is basically a measurement of how well the light source shows an object's colour. It's a scale from one to 100 with 100 showing colours at the same level as daylight (considered a perfect colour preserver) and lower levels indicating some colour vibrancy might be lost when shown in that light. (Remember that "daylight" here means the light itself, not the colour temperature of the light.)
In short, the lower the CRI the less accurately colours will be reproduced. For example, an apple that has a bright red colour in sunlight may appear dark pink under the lower CRI lights. It's likely you will have had the experience of looking at an item in a shop, for example, and then taking it outside and discovering it's a different colour in daylight. This is why some art galleries and museums, require bulbs 95+ CRI to allow the visitors to see the "real" colours.
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For diving, higher CRI does make a considerable improvement to the quality of video or photographs. A greenish hue can present with lower CRI lights (70 and minus), even in clear waters or close to the surface, which can be an issue for pale skin tones and other lighter colours. Post-production may struggle to fix this, depending on its severity.
While professional photographers would usually recommend a CRI of 90 or above, that doesn't mean a hobbyist needs that high a CRI - but it is worth understanding the index as it can be key to understanding some light conditions and photo effects.
If you're intent on getting professional-level product though, and CRI is something you care about, then we'd probably steer you towards Keldan lights, which have a range of CRI levels available, including a couple that have CRI of 95+. [here and here]
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All the best with your underwater photography! We hope as the weather warms up you find more opportunities to get out there and get creative!
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Happy to help.
These are just two aspects of how light and colour can interplay with underwater photography. Experienced photographers will understand there are a multitude of issues in this area. If you're having issues with your colours not coming out right, give us a shout!
You can find us over at our website or email or call, we're happy to help!
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