Jump to content


Graggs

Member Since 23 Jul 2011
Offline Last Active Jan 17 2014 01:30 AM
-----

#341475 Anyone tried: Mangrove K-VS-12L12 Lights (18240 Lumens)

Posted by Graggs on 06 January 2014 - 11:06 AM

I can't comment on the individual products above or their suitability, but for the benefit of people reading this, here is a quick explanation of CRI / Colour Temperature and other interesting LED light output stuff.

 

The CRI shouldn't be confused with the colour temperature (expressed in °K .... degrees Kelvin)

CRI stands for Colour Rendering Index and is an expression to determine how faithful colours 'look' under a given light source. 

°K .... degrees Kelvin is an expression of colour temperature, the lower the figure, the nearer to the warm end of the spectrum (fire / candle) the higher the figure, the nearer to the Blue end of the spectrum. Daylight being about 5,000°K ~ 6,500°K

 

As an illustration, a Tungsten Halogen light source of around 3,000°K can have a CRI >95 and by comparison a fluorescent light source with a colour temperature of 5,000°K might have a CRI of <75.

 

Part of this is due to the spectrum of light that the light source is emitting. The 'Spectrum' being all the various colours (think rainbow or prism),

In the image below, you can see the Halogen lamp (middle) emits a continuous range of colours whereas the fluorescent (bottom) has whole sections missing (or too dim to be any use). 

301px-Simple_spectroscope.jpg

 

LED's have much the same problem as the fluorescent above, they not only have major deficiencies in certain colours (technically wavelength) BUT also have 'spikes' in some colours - the right hand image below shows our Tungsten light source.

LED_Comp_Sprectrum.jpg

 

LED's are notoriously bad in the CRI department. But they are getting better. You also have to treat the manufacturers CRI readings with caution, as they can be fudged.

 

 

A result of this can be seen below, the image on the left is lit with Tungsten and the right with White Phosphor LED source. Look at the skin tone of the right hand image, the lack of correctly coloured light (or light deficient in certain wavelengths) has rendered the skin wrong. In contrast the blue spike in the LED light source on the right has made the dress look too blue (in fact it's changed the colour of the dress altogether).

LED_Model_Comp.jpg

 

And this is before you shine the light through water with particles in it or take into account the degradation of the LED over time.

 

Another consideration... but way outside the scope of this thread is the sensors ability to record this information, i.e how sensitive it is to various colours or wavelengths.

 

It's all relative of course and most dive sites are NOT offering perfect filming opportunities. But I felt the above distinction might help?

 

A couple of the above images come from this old thread, which is worth a read if you want to expand on the above. It is old but still relevant to some of the points above.

http://www.cinematog...showtopic=52551