Industry standards suggest optimal voltage drop percentages for efficient lighting systems:

• 3% Voltage Drop: Ideal for most low-voltage landscape lighting systems to ensure optimal performance and lamp life.
• 5% Voltage Drop: Generally acceptable for most landscape lighting applications. Performance and lamp life may be slightly impacted.
• 10% Voltage Drop: This is the maximum acceptable voltage drop for many LED fixtures. Exceeding this can lead to noticeable dimming, inconsistent light output, and premature lamp failure. It's highly recommended to redesign if your calculation is above 10%.

These guidelines are general recommendations. Always consult manufacturer specifications for specific fixtures and transformers.