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Old 25th March 2014, 04:48 PM
John King John King is offline
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Default Judging the colour balance

For as long as I have been printing RA4 I have always used a blue tungsten bulb to assess the accuracy of the colour balance (I always dry the print first). I was considering changing over to LED lighting to do the assessment, but do not know the colour temperature of LED lights.
Ideally I need something in the range of 5000-5750 degrees K.

Can anyone give me a rough idea what the colour temp of an LED light is before I go out and buy one.
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Old 25th March 2014, 05:11 PM
marty marty is offline
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Hi there. A quick peek at the Osram catalog reads 2700K for consumer classic bulb shape lamps. Though there might be some specialty items with colder light temp.

Cheers, M.
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Old 25th March 2014, 05:18 PM
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A LED video/camcorder light is likely to be about right since they're supposed to be daylight-balanced.
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Old 25th March 2014, 06:43 PM
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A very tricky subject. There seems to be all sorts of claims and counter claims about what is theoretically correct.

My personal opinion opnion is the best option is the same light the print will be viewed in when hung on the wall or wherever. And there's the problem, you just don't know what that light will be unless its your own house/office and even then it will change from daytime to nightime.

Any final position for the print will be affected by the lighting used in the room and the wall and ceiling colour which will give a colour cast and affect the colours seen in the print. Where does that leave you? Well it means you can only ever get it into the ball park as far as getting colour right regardless of whether you use daylight balanced to some exact specification such as D50.

So in short I wouldn't get overly concerned about it providing your light source is ballpark daylight. But then again if you want your print colours to look good in the evenings when you have your house lights on, which probably aren't daylight balanced, then maybe not.

And what does daylight balanced mean anyway? Daylight outdoors colour temp varies all the time from winter to high summmer, from dry air to high humidty, from cloudless sky to heavily overcast. Light temp is changing all the time in daylight.

It really only gets critical if you are doing colour work where a client demands a specific standard must be adhered to.

Last edited by Argentum; 25th March 2014 at 06:59 PM.
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Old 26th March 2014, 08:31 AM
John King John King is offline
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The blue bulb method has served me well for the past 30 years but I am conscious that they will not always be available with the switchover to LED and Fluorescent lighting so want to jump before I am pushed so to speak.
I require the colour balance to be accurate under these lights, so if viewed in other lighting I can ignore any discrepancies, knowing that they are accurate in daylight.

The 4 prints I did last night were judged by the blue bulb and by natural light this morning they are spot on. (Incidentally my blue bulb 'blew' last night so now I only have one left!)
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Old 26th March 2014, 03:12 PM
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there's probably something at following website that suits your needs.

But looking around it seems daylight is considered 6500K. The day bulbs in this site seem to be 6000K but I only looked at a couple.

http://www.jacksta-energy.co.uk/LED-GU10-s/29.htm
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Old 26th March 2014, 03:31 PM
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6500K is a bit blue for daylight unless in open shade. Sunlight is usually around 5400K which is what most LED camcorder lights are set for.
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Old 26th March 2014, 03:38 PM
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one of these should fit a standard 240v screw in desk lamp

http://www.jacksta-energy.co.uk/E27-...e27-3w1-dw.htm
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Old 26th March 2014, 06:37 PM
JOReynolds JOReynolds is offline
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I have not yet seen LED luminaires that claim to be 'colour-matching'.
There are two types of 'white' LED lighting. The commonest quotes a colour temperature, which is risky because a glance at the emission spectrum shows it to be bumpy, unlike a tungsten filament or sunlight. The light-emitting chip produces blue light at 420...460nm, which passes through a phosphor layer that absorbs some of the blue light and re-emits yellow-orange light. The phosphor is often built into each individual LED package. Alternatively, an array of blue LEDs emits through a translucent window containing the phosphor. The combination looks whitish but a quoted colour temperature is only an approximation because there is actually a distinct bump around the blue and another, less pronounced, at the yellow-orange. The ratio simulates daylight or tungsten but there may be differential fading, so the colour could change over time.
The other type synthesises white light from discrete blue, green and red LEDs. It can be tuned to replicate tungsten or daylight.
For colour matching the latter type is to be preferred because, if they are lightly driven, the three LED types fade at roughly the same rate. And could be re-tuned to achieve the original colour balance.
Developments in LED technology are proceeding apace but, at present, 'color matching' tri-phosphor fluorescent tubes are still regarded as the standard in the graphic arts industry (ISO 3664:2009). They also degrade with time and are often wired with a timer to indicate when to change the tube.
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