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Projects2026

Daylight

An outdoor daylight and vitamin D planner for iPhone that pairs local solar geometry with UV tracking to calculate safe sun exposure windows and vitamin D synthesis. The codebase is feature-complete in source while launch gates remain.

Stack
Local-first
on-device solar math
2 bounds
target dose vs protect limit
83 tests
solar and safety verification
0 ads
private local architecture
§01The workThe product

Native iPhone app for daylight and vitamin D timing, feature-complete in source with launch gates remaining.

Daylight
SwiftUI · local solar math · HealthKit

Outdoor daylight planning with clear exposure boundaries.

Daylight pairs on-device solar calculations with elevation-aware UV forecasts to plan safe daylight windows without gimmicks.

Daylight Today screen with solar stage, UV index, and exposure window.
Daylight session prep screen with profile defaults and outdoor conditions.
Daylight history ledger with logged outdoor time and exposure records.
The productToday screen. Solar stage, UV index, and exposure window. / Session prep. Profile defaults and outdoor conditions. / History ledger. Logged outdoor time and exposure records.
§02The pipelineEnd-to-end flow
01

Profile

Saves skin response and coordinates locally without an account.

skin type · coordinates
02

Calculate

Computes solar angles locally and merges elevation-aware UV data.

solar math · UV forecast
03

Track

Counts exposure progress and alerts before reaching burn limits.

live timer · protect alert
04

Sync

Writes confirmed outdoor minutes directly to Apple Health.

HealthKit · Time in Daylight
§03What I builtPieces that compound

Local solar math, dual-boundary engine, session tracking, and HealthKit sync.

Dual-boundary targets

Separates useful daylight synthesis from the protect boundary to prevent burns.

50% vs 80% MED

Elevation-aware UV

Pulls forecast UV that already accounts for elevation instead of stacking fake multipliers.

no double multiplier

Confirmed minutes only

Writes only verified outdoor time to Apple Health rather than modeled blood levels.

HealthKit integration
§04Build rulesSafety · evidence · honesty

Conservative assumptions and honest bounds.

Selected rulesevidence-first posture
  1. Keep target exposure separate from the hard protect boundary.
  2. Write only confirmed duration to HealthKit as Time in Daylight.
  3. Never apply duplicate altitude multipliers to elevation-aware forecasts.
  4. Run all solar geometry calculations locally on the device.
§05StackEvery tool earns its line
SwiftUI / InterfaceHealthKit / Health syncSolar geometry / On-device mathWidgetKit / Glanceable stateiOS 18+ / Target
§06ArtifactsReceipts and public proof

Native app, estimation engine, and test suite.

Daylight for iPhone

Native SwiftUI app with a solar dial, live timer, history ledger, and home widgets. Feature-complete in source.

native iOS app
Dual-boundary engine

On-device solar model combining local geometry and elevation-aware forecasts to separate target doses from burn limits.

on-device model
Safety test suite

83 tests covering solar geometry, reboot recovery, timezone resilience, and health-write safety.

83 tests green