PD	Parkinson’s disease
PBM	Photobiomodulation
LLLT	Low-level light therapy
RCT	Randomized controlled trial
PRISMA	Preferred Reporting Items for Systematic Reviews and Meta-Analyses
PROSPERO	International Prospective Register of Systematic Reviews
MeSH	Medical Subject Headings
RoB 2.0	Cochrane Risk-of-Bias tool, version 2
ROBINS-I	Risk Of Bias In Non-randomized Studies-of Interventions
MD	Mean difference
REML	Restricted maximum likelihood
HKSJ	Hartung–Knapp–Sidik–Jonkman
CI	Confidence interval
MDS-UPDRS-III	Movement Disorder Society-Unified Parkinson’s Disease Rating Scale, Part III
TUG	Timed Up and Go test
TMWT	Ten-Meter Walk Test
MCID	Minimal clinically important difference
DBS	Deep brain stimulation
SD	Standard deviation