RLOD#20 (2020.05.26) 1998 Philips DL 50

The DL 50 is a larger version of Philips's 35 W D2 xenon metal halide automotive lamp, intended for off-road lighting and as a compact source of light for instrument illumination (microscopes, etc). Its higher light output of 4.8 klm (vs. 3.2 klm for the 35 W type) does not make it road legal, but this was nevertheless a popular lamp in the custom car community, who affectionately dubbed it “Fat Boy” due to its distinctive look compared to the slim D2. Some even drove it at 75 W on a special electronic driver in order to get more light out of it (about 7.4 klm), but this came at the expense of life. Interestingly, if the DL 50 shares the same sodium-scandium fill chemistry as its standard 35 W counterpart, its xenon fill pressure is reduced in order to facilitate ignition at lower voltages (well below the usually required 10‒20 kV), which enables simpler and cheaper control gears in instrument illuminators. A reduced ignition voltage also helps meet a key requirement in that application, i.e., limited electromagnetic interferences. However, two important criteria for automotive headlighting are no longer met, namely a 30 % light output right after ignition, and an instant hot restrike of the lamp. Both are not needed in the lamp’s intended applications however.