We examined the maximum bolometric peak luminosities during type I X-ray bursts from the persistent or transient luminous X-ray sources in globular clusters .
We show that for about two thirds of the sources the maximum peak luminosities during photospheric radius expansion X-ray bursts extend to a critical value of 3.79 \pm 0.15 \times 10 ^ { 38 } erg s ^ { -1 } , assuming the total X-ray burst emission is entirely due to black-body radiation and the recorded maximum luminosity is the actual peak luminosity .
This empirical critical luminosity is consistent with the Eddington luminosity limit for hydrogen poor material .
Since the critical luminosity is more or less always reached during photospheric radius expansion X-ray bursts ( except for one source ) , such bursts may be regarded as empirical standard candles .
However , because significant deviations do occur , our standard candle is only accurate to within 15 % .
We re-evaluated the distances to the twelve globular clusters in which the X-ray bursters reside .