Which type of light measurement would be most appropriate for assessing plant light needs?

Foot-candles is the most appropriate measurement for assessing plant light needs because it quantifies the amount of light that is received on a surface from a specific source. Specifically, one foot-candle is defined as the illumination produced by a one-candle power light source at a distance of one foot. This measurement directly relates to how well the light can support photosynthesis and overall plant health, making it critical in the context of horticulture and floriculture.

Lux, although it is a unit of illuminance like foot-candles, is based on the metric system and might not be as commonly used in certain agricultural practices in the United States. While it can provide useful information, foot-candles is often preferred for its more traditional application in this context.

Kelvins measure the color temperature of the light, indicating whether it appears warm or cool, which affects plant growth indirectly by affecting the kind of light spectrum plants are receiving. Watts, on the other hand, measures the power consumption of the light source, which doesn't provide an indication of how effective that light is for plant growth. Therefore, foot-candles is the best choice for directly evaluating the light needs of plants.