How many lumens do you need for outdoor lighting?

Far less than indoors. A wall light of 250 to 750 lumens beside a front door is plenty, because in the dark your eyes are already set for little light. There is no standard saying how much you need, but there is a guideline saying when it becomes too much.

Why outdoors calls for different numbers

Indoors you calculate in lumens per square metre, because you want to light a whole surface evenly. Outdoors that does not work. There is no ceiling bouncing light back and no wall holding it in: everything you send upward or sideways is gone.

On top of that, your eye adapts. After ten minutes in the dark you see with a fraction of the light you need indoors. One bright lamp therefore often makes things worse: your pupil closes and everything outside the beam becomes a black hole.

The guideline is about the upper limit

The Dutch Lighting Society sets limits in its light nuisance guideline for how much light may fall on someone else's facade. These are split into environmental zones, taken from CIE publication 150:

• E1 nature reserves and rural areas far from settlements
• E2 suburban and rural residential areas
• E3 urban residential areas
• E4 city centres and areas with night-time activity

During the day and evening, at most 2, 5, 10 or 25 lux may fall on a facade, rising from E1 to E4. Between 23.00 and 07.00 that becomes 1, 1, 2 and 4 lux. Those are low numbers: an overcast day is already around 1,000 lux.

For an ordinary house in a residential street the practical translation is simple. Aim your lamp downward, keep it out of the neighbours' bedroom window, and fit a sensor rather than a lamp that burns all night.

What the insect story really says

Everywhere you read that warm light attracts fewer insects. That is only half true, and it is worth looking up.

Wakefield and colleagues compared four lamp types across eighteen sites in England in 2016, in Ecology and Evolution. Of all the insects caught, 54 percent came to the incandescent bulb, 24 percent to the compact fluorescent, 10 percent to cool white LED and 12 percent to warm white LED. So LED caught about half of what a compact fluorescent caught and four times less than an incandescent bulb, because LED emits no ultraviolet.

But between cool white and warm white they found no significant difference. The gain is in switching to LED, not in choosing 2700K over 4000K. So pick your colour temperature on atmosphere, not on midges.

What we carry and what it gives

Our wall lights sit in the range you need outdoors:

• Dano: 8 watts at 95 lumens per watt, so around 760 lumens, IP65 and a 45 degree beam
• Senso: 540 lumens, IP54, with a sensor
• Cob round: 510 lumens out of 6 watts
• Nomo: 250 lumens, rechargeable, IP44

For a front door, 250 to 500 lumens is enough to see a face and a keyhole. For a driveway or a back path you move towards 700 lumens per light point, but then two weak points beat one strong one.

What else to watch

The beam matters more than the lumen figure. A lamp that shines only downward puts more usable light on the path at 300 lumens than a globe of 800 lumens lighting half the garden and the sky along with it.

And look at the IP rating, because that decides whether it survives. What the digits mean is in Can an IP44 light be used outdoors? The difference between lumens and lux is in What is the difference between lumens and lux?