DIRECT sunlight as opposed to just daylight

Question

I have developed a veggie patch on my friend’s section because I live in a flat with no land attached. My patch gets DAYLIGHT, but little DIRECT SUNLIGHT. My friend says – “what’s the difference, it’s all light. Your veggies will grow fine.” Most probably they only need 5-6 hours of any kind of light per day. I know this isn’t true, that they need ‘DIRECT SUNLIGHT’ rather than just ‘LIGHT’ but unless I can explain the science behind this, any discussion will get nowhere. Is it to do with heat or purely the strength of the light or what?

Thank you in advance.
Emily Friedlander

Answer 1

You are correct that direct sunlight is important for many vegetable plants because it has higher light intensity. Plants are very sensitive to differences in light intensity that humans cannot detect. One of my horticulture professors once told me that light that appears twice as bright to us is actually ten times as bright, because our vision works on a logarithmic scale. But that same light will provide a plant with much more photosynthetic energy.

Direct light is needed for most fruits (and veggies that are really fruits, like tomatoes and cucumbers) to produce efficiently (they will probably produce something in shadier spots, but not as much as they would in bright sun), but leaf plants like spinach, kale, lettuce, etc. usually do fine in lower light conditions.

https://aggie-horticulture.tamu.edu/ornamental/a-reference-guide-to-plant-care-handling-and-merchandising/light-temperature-and-humidity/