The
HPL and the
Source Four were designed for each other. In fact, the S4 gets it's name from the "Four" stacked
filament sections being the light "Source." By moving the
filament into that structure, more light is given out in a smaller location, which is very desirable in a focused spot.
Older
axial spots that are designed for the longer length
filament can not take advantage of the tighter light source in the
HPL as the reflectors were configured to be optimum with the longer length filaments found in the FEL/FLK
etc.
Upgrading the lamp type in an older
axial unit requires several perimeters to fall in alignment:
1) Obviously, the lamp
base
2) The distance between the lamp
base and the center of the
filament. (
LCL)
3) The length of the
filament.
If the
base and the
LCL are a match, using a lamp with a tighter
filament in a
fixture designed for a longer
filament will not do any harm, but you will not get the same efficiency that you would in a
fixture designed for the shorter
filament. Conversely, using a lamp with a longer
filament in a
fixture designed for a shorter
filament will not only be inefficient, it may actually cause harm to the
fixture. This is because light and heat generated by the lamp that is not directed properly out of the
reflector area will tend to
build temperature in that area beyond what the
fixture was designed to deal with.