Calculator
Example data table
| Date | Sunrise | Sunset | Shade periods | Total shade | Sun-equivalent | Category |
|---|---|---|---|---|---|---|
| 2026-01-27 | 06:30 | 18:00 | Tree 09:00–10:30, Building 12:30–14:00, Pergola 15:30–16:30 (0.60) | 3h 00m | 9h 18m | Full sun |
| 2026-05-10 | 05:30 | 19:05 | Building 10:00–15:00, Tree 16:00–18:00 | 7h 00m | 6h 35m | Full sun |
| 2026-10-03 | 06:10 | 17:35 | Canopy 08:00–16:30 (0.70) | 8h 30m | 5h 30m | Part sun |
These rows are examples to help you understand the inputs and outputs.
Formula used
DaylightMinutes = SunsetMinutes − SunriseMinutes
The calculator works with same-day times and assumes sunset is later than sunrise.
Overlap = max(0, min(ShadeEnd, Sunset) − max(ShadeStart, Sunrise))
Each shade period is clipped to the daylight window before totals are calculated.
- TotalShade = sum(Overlap) (then capped to daylight)
- WeightedShade = sum(Overlap × Factor) where Factor is 0–1
- DirectSun = Daylight − TotalShade
- SunEquivalent = Daylight − WeightedShade
Use a lower factor for filtered shade so it reduces sunlight less strongly.
How to use this calculator
- Enter your local sunrise and sunset times for the day.
- Record when the planting spot is shaded during daylight.
- Add up to three shade periods as the shadow moves.
- Set a factor for filtered shade, like tree canopy.
- Press Calculate to see shade hours and light category.
- Download CSV for logs, or PDF for sharing and printing.
Why shade hours matter
Shade hours shape plant performance because photosynthesis depends on usable light. Many fruiting vegetables need at least 6 sun‑equivalent hours to set flowers reliably, while leafy greens tolerate lower totals. Tracking shade helps you avoid heat stress in summer and prevent slow growth in cooler seasons.
Typical light targets by plant type
Full sun beds often aim for 6–8 hours, herbs and tomatoes commonly thrive there. Part sun areas around 4–6 hours suit peppers, cucumbers, and many ornamentals. Part shade zones near 2–4 hours work for lettuce, spinach, and ferns, while under 2 hours is best reserved for deep‑shade natives.
Collecting field observations
Walk the site at consistent times and note when the planting spot enters or leaves shadow. If shade shifts, record multiple periods such as a morning tree shadow and an afternoon wall shadow. For better accuracy, observe over several days and use averages, especially near equinoxes when sun angles change quickly.
Using shade factors for filtered light
Not all shade blocks the same light. A solid building shadow behaves like factor 1.00, but canopy shade can be 0.50–0.80 depending on leaf density and season. Using a lower factor reduces the penalty, converting “shade minutes” into a more realistic sun‑equivalent estimate.
Interpreting outputs and planning beds
The calculator reports daylight, capped shade, direct sun, and sun‑equivalent time. If direct sun is low but sun‑equivalent remains moderate, plants may still perform well under dappled shade. Use the category label to group crops, then place sun lovers in the highest‑equivalent zones and reserve shadier pockets for moisture‑loving species. For long-term records, export CSV after each survey and compare seasons; small changes from pruning or new structures can shift light dramatically overnight sometimes.
FAQs
1) What are “shade hours” in this tool?
Shade hours are the minutes your entered shade periods overlap with the daylight window. The summary caps totals to daylight so results stay practical even if shade periods overlap.
2) Why does the calculator show “sun-equivalent” time?
Sun-equivalent adjusts shade by a factor. Dappled or filtered shade reduces effective shading, so the sun-equivalent value estimates how much usable light plants may still receive.
3) What shade factor should I use for tree canopy?
Try 0.50–0.80. Dense evergreen cover is often closer to 0.80–1.00, while light deciduous canopy can be nearer 0.50–0.70. Adjust after a few observations.
4) Can I enter more than three shade periods?
This version supports three periods to keep entry fast. If your site has more changes, combine adjacent intervals, or run multiple calculations and log them in CSV for comparison.
5) What if my shade periods overlap each other?
Overlaps may add up in the period list, but the top totals are capped to the daylight duration. If overlapping is common, merge periods or refine start and end times.
6) How accurate is this for my garden?
Accuracy depends on your observations. Using sunrise/sunset for the same day, recording times consistently, and averaging across several days typically produces better placement decisions than guessing.
7) When should I measure shade for planting decisions?
Measure near your planting season and again mid-summer. Sun angles change across the year, and growth or pruning can shift shadows. Seasonal CSV logs make these changes easy to track.