High-Power LED Datasheets

The Five Numbers That Decide a High-Power LED Design

A high-power datasheet carries dozens of parameters, but five of them determine whether your luminaire hits its photometric target at 50,000 hours. Read them in this order:

1. Thermal resistance, junction-to-case (Rθ J-C) — typically 4–8 °C/W for 1–3 W packages. This number, multiplied by dissipated power, tells you the temperature rise the heatsink must absorb.
2. Maximum junction temperature — 110–125 °C rated, but design to hold Tj at or below 85 °C for the L90 life target; every 10 °C reduction roughly doubles time-to-70%-output.
3. Flux bin at the stated test current — luminous flux is always binned (e.g., 100–110 lm at 350 mA). Design to the bin floor, never the typical value.
4. Forward voltage range — the min/max window at test current, typically 2.8–3.6 V. Driver selection and series-string arithmetic use the max for current headroom and the min for open-circuit protection.
5. Test current versus rated maximum — a part tested at 350 mA but rated to 1 A is telling you the photometric tables are not the ceiling; derate to 70–80% of maximum for long-life products.

Thermal Design Quick Reference

From Datasheet to Luminaire

Two of our deployment write-ups trace this exact chain: the municipal solar street light case shows bin-floor budgeting against battery constraints, and the UFO high-bay factory case documents a 5 W-class multi-die design held at L90 over 50,000 hours. For component-level reliability methodology, see the LM-80 lifetime estimation guide.

Frequently Asked Questions

Can I parallel two high-power dies on one driver?

Not directly. Forward-voltage mismatch makes current hog one die. Use separate constant-current channels, or a purpose-built multi-die package where the manufacturer has matched the dies internally.

What surge rating should the driver carry for street applications?

10 kV common-mode / 6 kV differential (IEC 61000-4-5) for pole-mounted luminaires on buried distribution, with line-to-neutral MOVs on the AC side of the driver.

How do I convert luminous flux to illuminance at the ground?

Illuminance (lux) = luminous flux (lm) × utilization factor ÷ area (m²). Outdoor pole installations typically realize a 0.35–0.55 utilization factor after optics, dirt depreciation (0.9), and lumen maintenance (0.9 at L90) are applied.