  The three main methods currently in use for estimating the excitation class
of planetary nebulae (PNe) central stars are compared and evaluated using 586
newly discovered and previously known PNe in the Large Magellanic Cloud (LMC).
In order to achieve this we ran a series of evaluation tests using line ratios
derived from de-reddened, flux calibrated spectra. Pronounced differences
between the methods are exposed. Diagrams were created by comparing excitation
classes with H-beta line fluxes. The best methods are then compared to
published temperatures using the Zanstra method and assessed for their ability
to reflect central star effective temperatures and evolution. As a result we
call for a clarification of the term `excitation class' according to the
different input parameters used. The first method, which we refer to as Exneb
relies purely on the ratios of certain key emission lines. The second method,
which we refer to as Ex* includes modeling to create a continuous variable and,
for optically thick PNe in the Magellanic Clouds, is designed to relate more
closely to intrinsic stellar parameters. The third method, we refer to as Ex
[OIII]/H-beta since the [OIII]/H-beta ratio is used in isolation to other
temperature diagnostics. Each of these methods is shown to have serious
drawbacks when used as an indicator for central star temperature. Finally, we
suggest a new method (Exrho) for estimating excitation class incorporating both
the [OIII]/H-beta and the HeII4686 /H-beta ratios. Although any attempt to
provide accurate central star temperatures using the excitation class derived
from nebula lines will always be limited, we show that this new method provides
a substantial improvement over previous methods with better agreement to
temperatures derived through the Zanstra method.
