In our last blog we discussed optical brightening agents, or OBAs. If you recall, these are the additives that make whites whiter.
Click here to read the previous post.
OBAs caused issues when they were first introduced to printing substrates, because viewing booth lamps were not designed to activate them. In addition, spectrophotometer lamps didn’t align with the viewing booth lamps, so they ‘saw’ the paper color with OBA content differently than we ‘saw’ the paper color. (Spectros will be discussed in the final blog of this series.) The industry began correcting this misalignment in 2009 by updating D50.
D50 has been the long-time standard lighting condition for the print industry. Until 2009 the standard (ISO3664) defined D50 to contain little to no UV radiation, meaning it didn’t quite simulate natural daylight. This also means prints enhanced with OBAs looked different when being approved in a viewing booth than they did outdoors. Obviously that’s an issue for prints meant to see the light of day.
In 2009 D50 received an overhaul to more closely simulate natural daylight. UV radiation was added to viewing booth lamps so OBAs would fluoresce, or appear whiter and brighter, during visual approvals. As a result, OBA-rich paper stock looked similar outdoors and in the viewing booth under the new 2009 standard.
NOTE: Change always takes time, so it was a few years before the last of the lamps rated to the pre-2009 D50 standard were purchased and installed. Unfortunately, many people only replace their lamps after they burn out, so although manufacturers no longer sell the old product, many booths still have the pre-2009 lamps. Some even have both the old and new D50 lamps in the same booth at the same time
The point of having a viewing booth is to standardize lighting conditions and avoid color surprises. Having conflicting lighting conditions in the same viewing booth does exactly the opposite. Speaking of bad ideas, daylight or grow light lamps are not the same as D50 standard lamps. Grow lights (5000K lamps) are not D50 lamps and should never be used in a viewing booth.
The new D50 standard lamps added UV light to viewing booths so visual approvals done inside looked similar to prints viewed outside. This was an important advancement for accurate print approvals on production paper stocks. Unfortunately, proofing stocks were slower to catch the OBA craze. This caused problems as shops began to replace their old lamps, because press sheets with OBAs and proofing papers without them no longer matched under the new D50 lamps.
As complaints rolled in, viewing booth manufacturers offered a quick fix: A UV filter was placed in front of the lamps to block UV light, and, in effect, converted the new lamps back to the old standard. This allowed proof stocks and press stocks to look the same again, because the OBAs didn’t activate with the UV radiation blocked.
This was a Band-Aid approach. The real issue was the proofing stock needed to incorporate OBAs to match the press stock. We are still in flux about how much OBA content proofing stock should have, but today you can purchase proofing and press stock with similar OBA content.
As time goes on, viewing booths and proofing papers will align with the industry’s use of OBAs. Visual approvals will contain fewer surprises, and the lamp challenges experienced after 2009’s D50 upgrade will become a thing of the past. We will all breathe a sigh of relief, turn to our spectros, and begin the journey once more.
Stay tuned for our upcoming blog on spectrophotometers, OBAs, and how D50 and M1 fit into the mix.