Well, car led headlight bulb is very popular now. Most people tend to choose LED instead of traditional halogen bulbs when they are going to buy a replacement car light bulb. But there is a puzzle, how bright a led light bulb can be?
If you search “LED headlight bulbs” on Amazon, you’ll get thousands of search results. Those led headlight bulbs on amazon are claimed that they can output 15000 lumens or even over 20000 lumens.
That is super bright stuff, you know, a Philips h11 halogen bulb may have only 1800 lumen output. Can a Led headlight have 6 times brighter or even 10 times brighter than a halogen bulb? We gotta investigate it.
We get to start from Lumileds Luxeon ZES LED. LUXEON ZES is a high-power 1.6mm x 2.0mm LED that is widely applicated to car headlamps and bike lamps. The early car LED headlight bulbs all used LUXEON ZES LEDs. Later, with the increase of competition and the decline of sales prices, new led headlights began to use some Chinese-made LEDs.
There are too many Chinese-made LEDs and it is hard to make their comparison in bulk. So we choose to take LUXEON ZES, a widely used LED as an example. In the specification of LUXEON ZES, there are complete data about light output, temperature, and current.
Led headlight bulbs are ordinary to use 6 pcs of LUXEON ZES LEDs to simulate the size and lighting position of halogen filament, so we take 6 pcs of LUXEON ZES LEDs to calculate the lumen output per LED headlight bulb. For the color we choose 6500k, it is the most popular color temperature.
According to the LUXEON ZES specification, when LUXEON ZES led is working at 85°C and the forward current is 700mA, the Luminous Flex is 270lm, and 6 pcs of LUXEON ZES LEDs will have 1620 lumen output.
When LUXEON ZES is working in the car headlight bulb, the forward current will be 1200mA when the car battery is on, so the LUXEON ZES light output will be 270*1.56.
The led light bulb just turn on, and the light bulb’s working temperature is still 25 °C. Compare to the 85°C, the light output of LUXEON ZES at 25°C is higher to be 270*1.56*1.13.
Stay the led light bulb on for 15-20 minutes, and the led light bulb’s working temperature raise to 160 °C. When Junction temperature reaches 160°C, the luminous flux of LED will reduce to 270*0.8.
While the bulbs installed inside a car headlamp, the temperature of the bulbs continue to increase, the ID driver will reduce the forward current to the LED light bulb to hold steady the application condition of the LEDs, preventing overheating. Normally, the steady current will be 15% lower than the initial current.
We calculate the light output of ZES at 160 °C application condition, the steady forward current is around 1200*0.85=1020mA, and the light output will be 270*0.8*1.36=294lm per LED.
A LUXEON ZES LED can emit 294 lumen output when turned on for 1 hour in a car headlight, 6 pcs of LUXEON ZES LED can emit 1763 lumen output.
That means, a 24 watt led headlight bulb can emit 1762 lumens on steady condition. This is the performance of brand LEDs.
If it is the high-power LED headlight bulbs, the working power raises to 55 watt, and the steady lumen output may be 1762*2=3524 lumens at most.