An umbrella shades you only if its shadow lands on you, and where the shadow lands is geometry, not luck. The World Health Organization’s ultraviolet radiation fact sheet tells you when the stakes are highest: the higher the sun, the higher the UV. This sheet adds the sums for a typical canopy, so you can see when holding it straight overhead works and when it does not. The WHO statements below are from that page, which we read on 1 November 2026. The sums and the notes are our own.
What the WHO says
- Sun elevation: the higher the sun in the sky, the higher the UV level. Levels also vary with time of day and time of year.
- Reflection: reflective surfaces such as water, sand and fresh snow increase the UV level.
- Protective measures: limit time in the midday sun, seek shade, wear protective clothing, a broad-brimmed hat and wraparound sunglasses, and use broad-spectrum sunscreen on skin that cannot be covered. Sun protection measures should be used when the UV index reaches 3 or above.
The sums
Our assumptions: a canopy 105 cm across, so a radius of 52.5 cm, held a set number of centimetres above the head, and a head about 20 cm wide, so 10 cm each side of centre. The canopy’s shadow shifts sideways from straight below by the gap divided by the tangent of the sun’s height above the horizon. The head stays in shade while that shift is 42 cm or less. The table gives the shift; “tilt” marks where the head is no longer covered.
| Canopy above your head | Sun 70° | Sun 50° | Sun 30° | Sun 15° |
|---|---|---|---|---|
| 20 cm | 7 cm | 17 cm | 35 cm | 75 cm (tilt) |
| 30 cm | 11 cm | 25 cm | 52 cm (tilt) | 112 cm (tilt) |
| 40 cm | 15 cm | 34 cm | 69 cm (tilt) | 149 cm (tilt) |
How to read it
- High sun, 70° or 50°: the shift is small even with a 40 cm gap, so hold the canopy level and overhead. This is also when the WHO says UV is highest.
- Sun at 30°: a 20 cm gap still covers the head, but 30 cm or more does not. Lower the canopy, or tilt it toward the sun.
- Low sun, 15°: the shadow lands well to one side at any gap in the table. Tilt toward the sun, or step so a wall or tree does the job.
- Below the head: the shift grows with the gap. At a 50° sun a point 1 m below the canopy sees its shade land about 84 cm off to one side, so a 105 cm canopy covers head and shoulders better than hips and legs.
- From the side and the ground: shade overhead does not block light reflected from water, sand or snow, which the WHO says increases UV levels. A hat and sunscreen still matter.
Finding the sun’s height
NOAA’s Global Monitoring Laboratory publishes a Solar Calculator that lets you look up the sun’s position for a place, date and time. Put in your location and the hour you will be outside, and use the sun’s height above the horizon in the table. Rough guide: the sun is highest near midday and lower at each end of the day, and lower in winter than in summer.
One option
Disclosure: xzvzx and Calm Eden have the same owner. Calm Eden’s guide to clip-on and clamp umbrellas explains why a clamped canopy needs re-aiming as the sun moves, because it cannot tilt itself. The Haven Umbrella opens to about 105 cm, the width these sums use, and it is held in the hand, so you can tilt it as the sun drops. That figure is the maker’s statement, and the shade sums are ours and assume a level canopy at the heights shown.
In short
- High sun means high UV and overhead shade: hold the canopy level.
- Low sun throws the shadow sideways: tilt toward the sun or lower the canopy.
- A canopy shades head and shoulders best; keep the hat and sunscreen.
Source: World Health Organization, Ultraviolet radiation, read on 1 November 2026. The geometry and notes are our own.
Common questions
Why does the sun's height matter for an umbrella?
The WHO says that the higher the sun is in the sky, the higher the UV level. A high sun also drops the canopy's shadow almost straight down, so overhead shade works. A low sun throws the shadow sideways, away from you, so the canopy has to be tilted toward the sun.
How far does a canopy's shadow shift?
By the gap between the canopy and the part of you being shaded, divided by the tangent of the sun's height above the horizon. For a canopy 30 cm above your head and a sun 50° high, that is about 25 cm. This is our own geometry, not a WHO figure.
Does an umbrella shade your legs at midday?
Not much. At a 50° sun, a point 1 m below the canopy sees its shade land about 84 cm off to one side, so a 105 cm canopy keeps head and shoulders in shade and leaves the lower body mostly in sun.
Should I tilt the umbrella toward the sun?
Yes when the sun is low. Tilting toward the sun moves the shadow back onto you. When the sun is high, hold the canopy level and overhead.
Is shade enough protection?
The WHO lists seeking shade among its protective measures and says to limit time in the midday sun, wear protective clothing, a broad-brimmed hat and sunglasses, and use broad-spectrum sunscreen on skin you cannot cover. It also notes that reflective surfaces such as water, sand and fresh snow increase UV levels, which a canopy overhead does not block.