We estimated leaf area index (LAI) in a needle-leaved forest and a bro
ad-leaved orchard using four instruments which measure fractional ligh
t penetration through the canopy. Gap fraction data were analyzed by a
one-dimensional inversion model or by using the Beer-Lambert Law. Ins
trument and analytical technique both had a strong influence on calcul
ated LAI. There was no consistent pattern of LAI results among instrum
ents so no simple cross-calibration can be offered. Three of the four
instruments accurately estimated orchard LAI when used with one or the
other analytical technique. In addition to performance, practical con
siderations including cost, sampling, and data analysis were also comp
ared among the instruments. Because the instruments do not provide con
sistently accurate LAI estimates, LAI should be independently corrobor
ated before use in any particular situation. These instruments may be
most useful for relative LAI comparisons in a specific canopy type whe
n a single combination of instrument and analytical technique is emplo
yed.