Well, this was a first for me...first time I've ever bought a complete lighting fixture just because I wanted the lamp!  This was spotted in our local Tesco supermarket.  A complete table lamp, complete with the PL-C lamp pictured here and a ballast unit...all for a few pence short of £5.  The package consisted of a small wooden based table lamp, the PL-C lamp itself, and a magnetic ballast built into a somewhat large plug in unit, similar to they type commonly containing low voltage power supplies.

This lamp is one of Philips' extensive PL range of non-retrofit compact fluorescent lamps.  When compact fluorescent lamps started to become a common sight, Philips were the first to spot the idea that the lamps need not be directly connected to the ballast as with the type of lamps you see designed to replace conventional incandescent ones.  This meant that a whole new world could be opened up to the designers of the opportunity to use these extremely compact lamps in applications where previously only miniature fluorescent tubes or incandescent lamps could have been used.  The PL series are available in a variety of styles, the PL-C as shown here, a two-tube version in high and low wattages (The PL-L and PL-S respectively), a recently launched high output version in wattages of up to 120W (PL-H), a version making use of U shaped tubes rather than the linear ones here, the PL-T, and even a special version of the PL-L designed for use in low temperature environments.  All of these are available in both 2 and 4 pin versions - the significance of this is explained below.

This lamp is fitted with a G24d cap - which will look exceedingly odd to you if you've not seen one before!  The two pin cap on this lamp contains a conventional glow-bottle starter and RF suppression capacitor in the square section.  This has the added advantage that a new starter is fitted with each lamp - an important feature as the cycling as the end of lamp life when connected to a magnetic ballast is very hard on a starter, and a faulty starter could end up sticking and destroying a perfectly good new lamp.  It also has the potential to cause ballasts to overheat and fail.  The fitment of a new one with each lamp negates this problem entirely however.  Having the starter and capacitor wired internally into the lamp does preclude this from operation on electronic control gear though.  It was for this reason that four pin versions of the various lamps were released a few years later, with direct connections to each of the lamp electrodes, and no internal starter.

The unusual straight four tube design of this lamp (and others in this range) is one of my favourites when it comes to lamp design, not least because it was one of the first that I started seeing.  It does help in functional terms too, due to one of the characteristics of fluorescent lamps (and in fact all metal vapour lamps).  The efficacy of these lamps is determined by the vapour pressure in the lamp, this in turn is determined by the temperature of the coldest point on the lamp wall - as the metal dose will condense there.  In the case of a low pressure mercury vapour lamp such as this, a low vapour pressure is desirable - hence as low a cold spot temperature as possible is desirable.  In the case of this style of lamp, that cold spot is created by leaving a small dead space at the end of each of the parallel tubes.  Due to the fact that this area is not part of the path followed by the discharge - hence it is further from the centre of the discharge column, the wall temperature is far lower than anywhere else.  This is a simple idea to implement, and works very well for small lamps such as this.  Unfortunately on higher wattage lamps, this dead space needs to be quite large due to the higher temperatures present, meaning that the lamps tend to be slightly longer than those using other methods to control vapour pressure such as external amalgams.  The ability to control the cold spot temperature like this however does lend a certain flexibility to lamp designers though, in that they can alter the size of the dead space at the end of the tubes to aim for the correct vapour pressure to be achieved at different ambient temperatures.  The PL-L range for instance has a smaller dead space at the ends of the tubes, allowing it to operate best at lower ambient temperatures.  I have noted in Aberdeen City, that the PL-L lamps are particularly popular choices for use in the fixtures used to provide night time illumination inside bus shelters.