cold vs warm light

[buddhasummer]

can anyone explain to me what is the difference between warm light and cold light, it would appear warm light has a lower lux than cold light but Im not exactly sure what this means. Im guessing the brightness is different. What does this mean in real diving terms, i.e. what is visually different? are the differences used for different applications eg photography? Thanks to anyone who can assist. Cheers

 

[wquiles]

Very good question, but there are no absolute answer, as there is a subjective side to the answer.

From a performance point of view, get the brightest light you can, specially those with the cool white LED's (more bluish) as those will give you best range/throw. However, from a subjective point of view, it will depend on what "tint" you personally like to see - what do you consider "normal" or "correct".

Most folks like a "white" light, one that tends to show the true colors at night - something resembling the full spectrum of daylight - that is hard to achieve in any light. For example, a well driven SureFure M6 with the high output MN-21 incandescent bulb gives out what most consider a perfect beam, and perfect color, at about 600 lumens out the front of the light. An LED light, on the hand, tend to be more "blue", and not so "warm" as a well-driven incandescent bulb. In this build of mine, you can see clearly what I mean in terms of tint:

Beamshot #1 – Pointing to the side of my neighbor:
- Ambient

- Surefire M6 with Regulated HDM6 LiIon pack – MN21 bulb

- Ostar 600-800 Lumen High Power LED light with a cool or bluish tint

Beamshot #2 – Pointing to a group of trees across the street:
- Ambient

- Surefire M6 with Regulated HDM6 LiIon pack – MN21 bulb

- Ostar 600-800 Lumen High Power LED light with a cool or bluish tint

Beamshot #3 – Pointing down the street, so that you can see more of the sidebeam:
- Ambient

- Surefire M6 with Regulated HDM6 LiIon pack – MN21 bulb

- Ostar 600-800 Lumen High Power LED light with a cool or bluish tint

Now, specially when looking at trees and the grass, which one to you looks more natural?

 

[wquiles]

Here is another example. This time I am using the M6 as a reference, but comparing it to a single high power LED light (600-700 lumen) and a VERY high power 3x MC-E light with a theoretical 2400 lumen output.

Lights used:
1) Surefire M6 - MN21 - Regulated LiIon battery pack, fully charged.
2) My own P7 Barbo super Host - Direct Drive from 18650 LiIon cell, fully charged.
3) New Super Barbo Light with 3x MC-E M-bin, Direct Driven from 2x IMR26500 cells, with 0.21Ohm resistance

Group 1: Side of other house next door
Baseline picture - no flashlights:

M6:

Barbo P7:

Barbo 3x MC-E:

Group 2: Street looking into trees
M6:

Barbo P7:

Barbo 3x MC-E:

Group 3: Looking deep into the trees
M6:

Barbo P7:

Barbo 3x MC-E:

Comparison side-by-side. M6 on the left, 3xMC-E on the right

Waking along a sidewalk:
M6:

Barbo 3x MC-E:

Once again, which one looks more natural to you?

 

[wquiles]

Final example, comparing LED with cool white/bluish tint, to another LED (of similar power/output/beamshape), but using a warm white LED:


Set 1:
First the P7 cool white, then the MC-E neutral tint:

Set 2:
First the P7 cool white, then the MC-E neutral tint:

And now, side by side. Guess which one has the warm white LED?

Will

 

[fppf]

To answer your question more directly, "warm" and "cool" refer to "color temperature" of a light source. It does not have anything to do with brightness of a source, just the color it outputs.

The Temperature is measured in Kelvin and roughly relates to the temperature of the plasma that is generating the light in the sun. The higher the Kelvin the more "blue" the light looks, the lower the Kelvin the more "red" it will look. Now the big snafu in this whole thing is that "warm" lights actually have a lower color temperature or kelvin rating than "cool" lights. That's because people connect more reds with being "warm" and more blues with being "cold".

Natural sunlight has a color temperature of about 6,500 kelvin. While light on a reef 30 feet down will have a color temperature of about 10,000 kelvin. This is because water filters out the reds and greens first and makes stuff look blue.

Halogen bulbs have a lower temperature, in the 3-4,000 range. This is because its a hot piece of metal making the light.

HID and LED bulbs tend to have higher temperatures, in the 6-10,000 range. This is because they use a silicone cell or an arc to make the light.

 

[Packhorse]

I have read a quite compelling argument that the tint of of light should match the tint of the water you dve in for best efficiency.

EG blue water use a blue tint ( Still a white LED) or green water a green tint. When viewed by them selves these LEDs dont really look blue or green buit when compared to each other you see the tint.

My preference is for a cool tint LED. They are more efficient than warm tints and seem to penetrate batter. Some argue that a more neutral colour is better but since the ambient light is so filtered by the water already I dont think it makes much difference except for photos or video, although this can then be correct by white balance.

 

[buddhasummer]

wquiles: thanks you very much for the effort in your reply with attached photos, much appreciated.

Ok I get the colour difference, the reason Im asking is Im looking at a wide angle light I can use for clear water OW reef type diving, I dont want a light that is so bright that it scares everything away, I also dont want a spot beam as Im not using it to signal or point out a street sign, so want a wide angle. I have been looking at Tauchlampen24 and they have changeable heads with their lights and this has my attention, specifically they make a 75 degree head with a "cold" 750 lumen head, also a "warm" 490 lumen 75 degree head and lastly a 240 lumen "cold" 75 degree head. I am wondering which would be best for my intended usage. Being that I live in NZ I cannot see them or test them and my knowledge of these matters is limited.

Any help or advice would be greatly appreciated, Packhorse? wquiles?

Cheers

 

[DA Aquamaster]

Warmer light - light with a orange to yellowish white appearance will have a color temperature of around less than 3500K.

White light has a color temp in the 3500 to 4000K range.

Bluish white light will have a color temp of 4000K or higher.

Sunlight in the middle of the day has a color temp of about 5500-5600K and is in the slightly bluish white range.

If you want what you are lighting up on the reef to look natural, you want a light with a color temp close to that of natural sunlight. That will be on the cooler side - slightly bluish white.

In my opinion 750 lumens in a wide beam is not overkill for a general purpose night diving light.

A Lumen is equal to one foot candle of light falling on one square foot of surface area. So 750 lumens would be 750 foot candles of light falling on one square foot. alternatively it could be 1 foot candle of light falling on 750 square ft. So the width of the beam is important as is the distance of the surface you are trying to illuminate.

In a very narrow beam 240 Lumens may be serious overkill, especially at short distances, but may not be enough at long distances. In contrast, a wide beam 750 lumens will most likely put a lot less foot candles of light on any given square foot. The farther the distance the less the illumination per square foot will be as it spreads out much faster due to the wide beam angle. (Less focused = more area covered with each increase in feet of distance to the subject.)

All of the lights you are considering have 75 degree head, so the variable are color temp and lumens. With the wide head, if you have anything close to decent viz and will be illuminating things at any distance, you want 750 lumens. If you plan on drifing over the top of the reef and nuking the nightlife at macro photography distances of a foot or less, even 240 lumens is too much, and in that case you want two lights, a large one for general illunmination and a very small one for closer inspection of fish etc at very close range.

 

[wquiles]

Like Packhorse and others have noted, blue wavelengths are the ones that penetrate deeper under water - here are some additional links:
Underwater Digital Camera ...

Colours under Water ...

Color Underwater ...

Does Color Matter for Fishing Lights? ...


Based on this, the "cold" light should give you more illumination at longer distances, as presumably the cold light has more "blue" compared to the warm source.

Being that I am into flashlights, I would second DA Aquamaster's advice in that you probably be better served with two flashlights, one being the cold/warm 75deg as your "high power" light, and a smaller (possibly hand held) for closer objects. Having a second flashlight is a good idea anyway as you should have always have a backup light anyway.

Will

 

[Packhorse]

75 degrees is a seriously wide angle. I can see it being useful for anything other than photography/video work.
For a dive light I would consider 20 degrees to be a wide beam.