KLY Explained: UV Intensity by Region and the Net Rating You Need

Editor’s Note: This article is part of our UV Stabilizers Guide. Visit the Hub for the full breakdown of UV protection — KLY ratings, stabilizer types (HALS vs absorbers vs carbon black), supplier verification, and 10-year cost.

KLY (kilolangley) is the amount of UV/solar energy that falls on one square metre of your site in a year — and it is the single number that decides how long an agricultural net survives the sun. The rule: choose a net rated above your region’s KLY, and for a permanent install aim for roughly 2×.

Get this number wrong and you buy a net specced for the wrong sun. In 28 years supplying UV-stabilized nets from Europe (70–100 KLY) to Australia (180 KLY), the most common “quality” complaint I hear is really a KLY mismatch: a net rated for European sun, failing in its second season under far stronger UV.

This guide explains what KLY means, gives you the regional map, the rating you need, and how to turn it into a net that lasts. It is part of our UV stabilizers hub.

What does KLY (kilolangley) mean?

KLY stands for kilolangley — 1,000 langley. One langley is one calorie per square centimetre, so one KLY equals 41.84 MJ/m² (about 11.6 kWh/m²). It measures the total solar (and UV) energy received on one square metre over a year. The higher a region’s KLY, the more UV your net absorbs, and the faster it degrades at a given stabilizer rating.

Every UV-stabilized net we make carries an indicative KLY rating — the UV “dose” it can absorb before losing about half its original tensile strength.

Which regions have the highest KLY?

UV intensity ranges from about 60 KLY in polar regions to 200+ KLY in desert zones, tracking latitude and climate. Australia, the US Southwest, the Middle East and North Africa sit at the top; Northern Europe and Canada at the bottom. These are industry field-reference figures for major agricultural regions:

Where do these figures come from? KLY values are derived from long-run solar-radiation records — the classic reference is Landsberg’s global solar-energy tables^[1] — cross-checked against national meteorological data such as the Australian Bureau of Meteorology’s UV climatology.^[2] They are planning-grade averages; your exact site shifts with altitude, cloud and reflection, so treat them as a starting point, not a guarantee.

KLY vs the UV Index: what’s the difference?

The UV Index in your weather app measures how strong UV is right now; KLY measures the total UV energy a surface collects over a whole year. A net does not fail from one hot afternoon — it fails from the cumulative dose, which is why KLY, not peak UV Index, is the number that predicts net life.

The two track each other but answer different questions. Australia, for instance, runs a summer UV Index of 11+ across the whole continent, yet Tasmania drops below 2 in July^[2] — the annual figure (~180 KLY) smooths those swings into one planning number. Use the UV Index to decide when to wear sunscreen; use KLY to decide which net to buy.

How does KLY decide a net’s lifespan?

“Lifespan” is the point where a net retains 50% of its original tensile strength — not the day it looks worn. A net’s KLY rating tells you how much UV dose it can take before crossing that line, so its real service life depends on your region’s KLY.

A worked example from our own production: orchard netting built to 700 KLY stability lasts about 4+ years in California (≈160 KLY) and 5+ years in Spain (≈120 KLY) before dropping below 50% strength. Same net, different sun, different life. For high-KLY regions that justify a permanent structure, a heavier Leno woven net carries a higher KLY rating than a seasonal drape net.

What KLY rating do I need — and how long will it last?

Match the net’s KLY rating to your region with margin, then read expected life off the product. As a planning guide:

Why the margin? UV dose varies from year to year, degradation accelerates as the net ages, and heat above 40°C speeds it up. A rating comfortably above your average KLY buys a buffer against bad years — which is why permanent installs aim for roughly 2× the regional figure rather than just matching it.

How do you use your region’s KLY when buying?

Find your region’s KLY, choose a net rated above it with margin, confirm the rating with a test report — but check the material first.

1. Find your region’s KLY from the table above (or your national solar-radiation data).
2. Pick a net rated above it, with margin for a multi-year permanent install (roughly 2× for the longest-life products).
3. Ask for the KLY rating and the test report (ASTM G154 or ISO 4892), and match the batch number to your shipment.
4. Check the material first. A KLY rating only delivers on adequate yarn weight (GSM) and 100% virgin resin — a thin or recycled-resin net cannot be saved by a high rating, because there is not enough sound material for the stabilizer to protect.

For the wider picture — how UV stabilizers work, HALS vs absorbers, and 10-year cost — see the UV stabilizers hub. Related reading: is HDPE UV resistant? and how UV degrades plastic.

Questions to ask your UV netting supplier

Before placing an order, ask your supplier these four questions. The answers quickly reveal whether they manufacture to a real UV standard:

1. What KLY rating is this net certified to, and can you show the test report? A serious maker has an ASTM G154 / ISO 4892 report tied to the production batch.
2. What UV stabilizer system does it use — HALS, UV absorber, or both — and at what loading? Quality nets use a HALS-led package, not a token dose.
3. Is it 100% virgin HDPE or recycled content? Recycled resin consumes the stabilizer and fails early behind the same “UV stabilized” label.
4. What is the yarn weight (GSM)? Two nets with the same KLY rating but different GSM are not the same net — compare grams per square metre, not just price.

Frequently Asked Questions

What does KLY stand for?

KLY stands for kilolangley — 1,000 langley. One langley equals one calorie per square centimetre, so one KLY equals 41.84 MJ/m². It measures the annual UV/solar energy falling on one square metre.

What is the difference between KLY and the UV Index?

The UV Index is an instantaneous measure of UV strength at a moment; KLY is the cumulative UV energy over a full year. Net life is driven by the annual dose, so KLY — not the daily UV Index — is the figure used to spec netting.

What KLY rating do I need for my region?

Choose a rating above your region’s annual KLY, with margin. Temperate Europe (70–100 KLY) suits roughly 360 KLY nets; high-sun regions such as Australia, Chile or the US Southwest (140–200 KLY) need 600–1080 KLY depending on the product and the life you want.

Is a higher-KLY region better or worse for my net?

Worse. A higher KLY means more annual UV dose, so a net of a given rating degrades faster. High-KLY regions need higher-rated nets to reach the same lifespan.

What is a kilolangley in kWh?

One KLY = 41.84 MJ/m², which is about 11.6 kWh/m² of received energy over the year.

Does a higher KLY rating always mean a longer-lasting net?

Only if the material is right. UV protection has a ceiling set by yarn weight (GSM) and resin purity — a thin or recycled-resin net will not last no matter how high its KLY rating, because there is not enough sound material to protect.

References

1. Landsberg, H.E. et al. World Survey of Climatology / global solar-radiation (langley) tables — the classic reference for annual solar energy (KLY) values by region. [Accessed via standard climatology references]
2. Australian Bureau of Meteorology. UV Index climatology maps. bom.gov.au — official data: summer UV Index 11+ nationwide, Tasmania below 2 in July.
3. Molina, A., Falvey, M., Rondánán, R. (2017). A solar radiation database for Chile. Scientific Reports. [Accessed via NCBI PMC]

By Kevin Lyu, EyouAgro — 28 years (since 1996) manufacturing UV-stabilized agricultural netting, from a factory with 8 production lines. Every net we make carries a KLY rating verified by lab and outdoor testing before it ships.

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