This is a small and very quick blog on the subject of how often to change D50 tubes, to the ISO 3664 standard, in order to maintain colour accurate viewing conditions. 
Well, the tube manufactories state a life of 2,500 effective hours. Of course the tube life is much longer, but they are not colour accurate after the 2,500 hours.
While many viewing booths do have a ‘timer’ which will remind the user to replace the tubes, many do not. So lets look at three common scenarios; effective tube lifetimes; over single shift, double shirt and 24/7 working.
Based on a single shift, 8 hours, with the viewing booth left on all day, (0f course nobody does that!), based on 5 working days a week, over 50 weeks results in needing to change the tubes every 15 months.
Based on a double day shift, 16 hours, with the viewing booth left on all day, based on 6 working days a week, over 50 weeks results in needing to change the tubes every 6 months.
Based on a 24 hour day, with the viewing booth left on all day, based on 7 working days a week, over 50 weeks results in needing to change the tubes every 3 months.
The second and third examples are common for pressrooms and the lightbooths on the end of presses.
Where light booths are used in prepress and in production offices then, if they do not have a ‘timer’, care will need to be taken in estimating the replacement periods, changing the tubes sooner rather then later. The costs are very small especially when compared with the possible implications of a poor proof to press sheet match due to ‘out of date’ tubes.
There are softwares available which can check both the colour accuracy of tubes and the uniformity of the lighting booth, using a spectrophotometer.
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Replacing D50 tubes should be part of the normal plant maintenance programme. It is a very small area of cost which will provide greater confidence when comparing and matching proofs and press sheets.
Also follow this link to my blog on the latest ISO 3664 standard for D50 lighting conditions:
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