Osram Decostar 51S 12V 50W Dichroic Halogen Lamp

Dichroic reflector halogen lamps such as this have been a common sight in commercial premises for a number of years now, and in the last couple of years have been slowly starting to nibble their way into the domestic market too. The lifetime being far in excess of non-halogen incandescents, the integrated reflector, "cool" beam, and relatively low cost (compared to PAR style reflector lamps), all appeal to the domestic customer. 

They are not as efficient as compact metal halide lamps, nor do they offer the same levels of lamp service life - in the domestic market however, the stratospheric cost of the control gear required for such systems puts them out of most peoples reach - whereas halogen lamps such as this require only a simple mains to 12V transformer to run (Though Osram recommend the use of their HaloTronic lamp driver to obtain the best service life and performance from the lamps).

A huge number of these lamps are produced cheaply by Chinese brands, and for the most part are perfectly serviceable.  However, this lamp by Osram is a good one to compare to in all aspects - this shows how a lamp of this type should be made.  The workmanship shown on this lamp is very good, and it shows in the performance.  This lamp is considerably brighter (and whiter) than a Chinese lamp of the same ratings I have (when run off the same power supply - and the off-brand lamp was drawing more current than this too), and has a beam that is barely comparable.  Perfectly smooth across its entirety, and my measurements showed the beam angle to be 40° - when the datasheets show it to be 38° - my measurements there are highly crude, so I'll go by Osram's figure!  The reason for this high quality beam is a combination of a supremely consistent and high quality dichroic coating on the reflector, and the use of an axial filament in the lamp.  A lot of the cheaper lamps use horizontal filaments, which tends to lead to a beam of a somewhat elliptical shape.

Osram of course also have fusing built into the mains version of this lamp (which is also fitted with a GU/GZ10 cap) to reduce the risk of the lamp envelope rupturing at the end of life.  Though that is a lesser problem with lamps of this type where the outer envelope is sealed.  Also, because of that seal, and the UV shielding built into this lamp, it is suitable for use in open fixtures.  The aforementioned fusing isn't necessary in the 12V version of the lamp however, due to the fact that the voltage is too low to sustain the plasma discharge which filament failure can initiate in mains voltage lamps.

Thanks to James Hooker (who also runs the excellent discharge lighting related website Lamptech), I was able to date this lamp to between July and September 1997.  He was also able to supply a good bit of information on the history behind lamps such as these.

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - General overview of lamp

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - Example of beam profile at roughly two metres

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - Detail of lamp cap and rear of reflector

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp illuminating my workstation from a distance of approximately two metres

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - General view of the lamp while alight

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - Overview of lamp packaging

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - Detail of lamp reflector

Osram Decostar 51S 12V 50W Dichroic Halogen Lamp - Displayed next to a ruler to show size of lamp

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16th June 2023: Changes to page format to improve readability on mobile devices, also some background code changes to improve search engine behaviour.