## The Hour Count: Why Christmas String Lights Die at 12,000 Hours (and the L70 Number That Decides) Every box says 25,000 hours, 50,000 hours, sometimes a number too lazy to count. I have sold string lights for nine years, and the number on the box is the least honest part of the package. The chip will outlive the socket. The question that decides whether a run is still bright next December is not printed anywhere. ## The Number Nobody Prints: L70, Not Lifespan A chip is rated by L70, the hour at which its output has dropped to 70 percent of day one. The datasheets we buy from our chip suppliers quote 50,000 hours at 85 degrees, and that is the number the retail box copies. It is a lab number. It assumes a thermal environment a 12-metre run on a roofline never gets, and a constant voltage that a cheap driver never holds. I keep a run from 2021 in my warehouse office. It has maybe 900 hours on it, and the last three C9s have gone from 2200 to 1900 kelvin on the meter. Nobody calls that a dead light. The customer does. The second hidden failure sits in the driver. A 12V constant-current driver that runs 4 degrees hot for five seasons will lose output before the chips do. Incandescent runs die at 1,000 hours and you feel no loss, because they were dim to start. An LED run that has lost 30 percent of its lumen output at hour 12,000 looks finished. The fix is not a better chip. It is buying the driver rated for your actual duty cycle, not the box claim. ## The Math That Decides the Year Do the arithmetic on a 12-metre C9 string at 10 watts running six hours a day across the season, roughly 40 days. That is 240 hours of burn in one year. A run rated at 12,000 hours has about 50 Christmas seasons in it before the L70 point, if the driver holds and the solder joints survive. The solder joints do not survive. The string heats when it is on and cools when it is off. That expansion and contraction cycle fatigues the lead frame connection over 3 to 4 seasons. This is why the 2nd and 19th bulb die on different years, and why a 30-bulb run reads as broken when it is 30 per cent dim. I test the fix in-store with a simple rule. We rotate stock every year, we sell by season, and we put the plug-end on a separate warranty because that is where 70 percent of returns actually land. The customer gets a run that is still 90 percent bright. The warehouse does not carry dead LEDs. ## The Fix That Holds Buy the run rated for the hours you will actually put on it. If it lives on a storefront for 12 hours a day across 200 days, the duty cycle is 2,400 hours a year, and a 12,000-hour rating has five years of margin. If it is a tree that gets two weekends, the margin is 40 seasons. When a run dies, do not chase the chip. Check the driver first. A 12V rail sagging to 10.5 volts under load will drop the far end of the string by 20 percent before a single LED has failed. Replace the driver, not the string. The plug is the other repair. A heat-shrink sleeve over the first two centimetres of the feed, and a spare run of the same chip in the box, is the entire fix I recommend to every installer I meet. It costs less than a coffee and it takes four minutes. The runs that fail in my warehouse never had the sleeve. They had the box number and nothing behind it. ### Frequently Asked Questions **How long do LED christmas string lights actually last?** A properly rated run reaches its L70 point at 12,000 to 25,000 hours of burn. At six hours a day across 40 season days, that is 40 to 90 years of use. The driver and the solder joints usually fail first, in year 2 to 4. **Why do christmas string lights go dim instead of dead?** Lumen depreciation. The chip output drops gradually toward the L70 point, and the driver rail sags under load. A 30-percent dim run is still 70 percent alive, but the human eye reads it as finished. **What kills a 12V christmas string light run first?** The plug, then the solder joints, then the driver. The chip is rated for 50,000 hours at lab temperature. The rest of the run is rated for far less. We carry [C7/C9 christmas string lights](/christmas-lights) and [warm white outdoor runs](/outdoor-christmas-lights) in our catalog, both with driver ratings printed on the box.