LC Blog
Seamless T5 lamps in Direct Fixtures
July 27, 2011 at 2:29 PM by Dr. Robert Davis
The continuous lines of light made possible by linear fluorescent lamps are difficult to implement in many applications because of the dark areas that appear at the lamp sockets. These “socket shadows” break up the clean line of light and can cause distracting patterns of strong brightness contrasts that many architects and lighting designers find objectionable. As discussed in a prior blog post, one approach to minimizing the effect of socket shadows in fixtures providing direct light is to use staggered lamping configurations, where the lamps overlap one another at the sockets.
Another approach was recently made possible by a new development in T5 lamp technology. At LightFair 2011, OSRAM SYLVANIA introduced a new family of “seamless” T5 and T5HO lamps. The geometry of these new lamps is such that the lamp bases are oriented at 90 degrees from the length of the lamp, rather than in-line with the lamp (see the illustration below). This geometry allows the ends of the lamps to be placed in close proximity to one another when the lamps are in continuous rows. You can see the new T5 seamless lamp in our Mod 44 Pendant.
By allowing the lamps to be aligned in a nearly unbroken row, the seamless lamps help to minimize the brightness differences that occur between lamps. If anything, the fixture design needs to consider that there may be MORE light at the lamp ends – socket brightness rather than socket shadow. But with the proper optical design, the brightness differences at the lamp ends will be much less noticeable with the new seamless lamps than with traditional sockets, and it may even prove to be superior to staggered lamp arrangements.
The biggest hurdle for fixtures that use the seamless lamps is the length of the lamps (and thus the fixtures). Because the three lamp wattages initially offered have unusual lengths (see the table below), fixtures designed for clean continuous light that runs end-to-end within the fixture will also be unusual lengths. This is fine for pendant fixtures, but poses some potential problems for recessed fixtures, if the designer wants a row length that is an exact increment of two or four feet to match a ceiling grid.
Want to avoid those pesky socket shadows? Now you have some options in how to do that.
Stephanie Seal 
