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one GrafiLite two GrafiLites - part 1 of 1 2 3

Published 01/02/2009

"There is only one thing more beautiful than one GrafiLite - two GrafiLites"

The Light Quality

This was measured when we first checked out a single GrafiLite in May 2008. The current results are essentially identical. The colour temperature is a little under 5,500 °K. The Colour Rendering Index, the measure of spectral purity of the light source, is around 85 units, just under that required for meeting the ISO 3664 standard (of 90 minimum). We also tested a few lights obtained from Lightbulbs Direct. Available via the web, Lightbulbs Direct offer a simple solution to obtaining some of these rather obscure bulbs and tubes as they carry a vast range, including the Phillips TLD 950 range, the best that are around. The fact that the proprietor is also a photographer means that they also talk sense when you ask them questions!

Having got the bit between our teeth we also went around maison McNamee measuring anything that had light coming from it. All the results are tabled. Some of the fluorescents in the house were truly awful. The very cheap tubes are heavily dosed with green phosphors to increase the output of light, at great cost to their colour accuracy, there is a massive spike in the green part of the spectrum, with all the problems that brings.

One of the finds of the exercise was the Prolilte Curly Helix from Lightbulbs Direct. This is a compact bulb with a standard bayonet fitting and ballast, so it fits as a direct replacement for any domestic bulb. We installed one above the Professional Imagemaker work station. It is rather strange at first and the cool colour is a bit of a shock each time you come into the room from other parts of the house. We are unsure how much we like it (we can always go into our calibrated, colour booth when we need to assess colour)

However, one of the things that started this quest was noting that metamerism is particularly bad for the domestic, warm-tone low energy bulbs, as well as being a little unpredictable. For example, the standard targets for scanners, the reflective IT8 type are made with wet chemistry prints - the greys are bright pink in warm LEB light. We also noted that the calibrated monitor looked 'better' when the room illumination was 6,500°K. There is a dilemma for studio photographers - do you sit your clients down in the clinical, cool light of ISO 3664 or in a more welcoming warm glow? Personally, I would keep the 65K for the print preparation area, but not the public areas.

Although this comparison shot has been done before, we set up the GrafiLite against an Ozram Dulux (in a reading light) and illuminated the same Q13 Kodak targets. The results are always a shock even though the outcome is predictable!

The Light Spread

The whole idea of the twin GrafiLite is to increase the illuminated area from the 10x8 nominal of the single unit to the A3 nominal of the twins. This is self-evidently true, the pool of illumination is twice the size, but the easy transport of the lights is retained (they do pack away nicely).

There are a few other things that having twin GrafiLites provides for, as follows:

Small-scale Artwork Copying

If you turn the GrafiLites into the vertical position, they make rather good copy lights for artwork up to about A3 size. This opens several possibilities especially if you are on the move or the artwork has to remain where it resides (for insurance or other reasons). If you place the GrafiLites about 18 inches apart and about 12 inches from the artwork you get a tolerably even illumination. We tested and measured this by shooting a plain white art board so that it was slightly underexposed (to make it come out grey). In Photoshop we then used the Threshold command to outline the illumination and then fudged the composite image together, as shown. The illumination is even to within 4/10 of a stop, even at this very close working distance and the exposure required was a managable 1/10s at f16 and 100 ISO. The colour quality was as good as you get with professional copy stands as the CRI for the bulbs is about the same.

The composite image shows the variation of luminance across the field of view of the artwork illuminated by two GrafiLites. The result is fairly typical of a two strip-light set-up.

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1st Published 01/02/2009
last update 21/07/2022 08:46:25

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