With 365 optimal days per year, Phnom Penh is among the world's best-positioned cities for solar vitamin D. The sun clears 45° — the minimum angle for effective UVB synthesis — for up to 369 minutes on peak days. The monthly calendar below shows exact windows all year.
| Month | Max UV | Optimal window (≥ 45°) | Extended window (≥ 30°) | Status |
|---|---|---|---|---|
| Jan | 9.8 | 10:03 – 14:15 (251 min) | 08:44 – 15:34 (410 min) | Optimal |
| Feb | 11.19 | 09:42 – 14:46 (305 min) | 08:33 – 15:55 (442 min) | Optimal |
| Mar | 12.58 | 09:16 – 15:01 (345 min) | 08:13 – 16:04 (471 min) | Optimal |
| Apr | 13.24 | 08:57 – 15:03 (367 min) | 07:55 – 16:04 (489 min) | Optimal |
| May | 13.19 | 08:52 – 15:01 (369 min) | 07:48 – 16:04 (496 min) | Optimal |
| Jun | 13.33 | 08:57 – 15:03 (366 min) | 07:52 – 16:09 (497 min) | Optimal |
| Jul | 14.38 | 09:02 – 15:10 (368 min) | 07:57 – 16:14 (497 min) | Optimal |
| Aug | 15.84 | 09:00 – 15:09 (369 min) | 07:58 – 16:11 (493 min) | Optimal |
| Sep | 16.2 | 08:57 – 14:53 (356 min) | 07:55 – 15:55 (479 min) | Optimal |
| Oct ← | 14.54 | 09:04 – 14:27 (323 min) | 07:58 – 15:33 (454 min) | Optimal |
| Nov | 11.72 | 09:29 – 14:00 (271 min) | 08:14 – 15:15 (421 min) | Optimal |
| Dec | 9.84 | 09:59 – 13:51 (233 min) | 08:35 – 15:15 (400 min) | Optimal |
The calendar above shows typical windows based on solar geometry. Below, today's cloud cover and your skin type are factored in for a personalised dose recommendation — updated live.
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In May, when UV peaks around 13.19, someone with medium skin (type III) typically needs about 5 minutes outside — arms and face exposed, no sunscreen. Darker skin takes roughly 2–4 times longer to absorb the same amount. If you're out during the extended window when the sun's a bit lower, budget closer to 30–45 minutes.
Surprisingly, yes — Phnom Penh gets enough direct sun for some synthesis even through the colder months. The windows get shorter, but they're there. Check the monthly table above for exact times.
Peak UV in Phnom Penh hits 16.2 around May — high enough to burn fairly quickly. Stick to your synthesis window (~5 min for medium skin), then put SPF 30+ on straight away. More time outside doesn't mean more vitamin D; it just means more burn risk.
Yes, but maybe less than you'd expect. Thin cloud cover barely makes a dent — you're still getting around 90% of UVB on a lightly overcast day. Once you're into heavy overcast territory (75%+ cloud cover), it's a different story: you might need to stay out about twice as long for the same effect. On a genuinely grey day, it's often not worth it. The calculator below uses today's actual forecast for Phnom Penh so you don't have to guess.
Sadly, no. Glass blocks UVB almost entirely — the exact wavelength your skin needs to make vitamin D. Sitting in a sunny room with light streaming in feels nice, but it won't do anything for your levels. You need to actually be outside, skin exposed to real, unfiltered sky.
Think of it this way: the optimal window (sun above 45°) is when UVB punches through the atmosphere efficiently — 10–20 minutes is enough for most people with medium skin. The extended window (30–45°) is the sun at a shallower angle, working through more atmosphere. UVB is still there, just diluted. Same result in the end, you just need 30–45 minutes rather than 15. Below 30°, the path is too long and most UVB gets absorbed before it reaches you, regardless of how long you stay out.