iamlucky13
Flashlight Enthusiast
- Joined
- Oct 11, 2016
- Messages
- 1,139
If you don't care about the method or detailed results, just skip to the pictures at the end.
Intro
With literally several thousand of these emitters now in circulation among CPF members, I thought it was worth taking some data on their performance when overdriven.
Before continuing, I want to thank those who have organized group buys or even outright shared Yuji 5mm emitters with others, including scout24, ma tumba, lampeDépêche, and K2-bk-bl-rd. This is part of what makes CPF a great community!
Disclaimers
1.) Treat my data as approximate, primarily for comparison to itself. I used a cheap, salvaged photocell I came up with my own rough calibration method for. My budget solderless breadboard also clearly had intermittent contact issues from handling that caused small fluctuations in some of the data. I'd be surprised if voltage and current measurements were off by more than 5%, but I'd be happy if I were able to confirm my Candela data are within +/- 50%.
2.) Anything above 30mA exceeds manufacturer specs. Worsening life span (potentially both hours and on/off cycles) should be expected the higher the currents go, but I have no data on how much worse. My testing lasted maybe 4-5 minutes at each current level as I moved my multimeter between measurement points, waited for stable readings, and recorded data.
3.) I tested a single sample. There may be variation in performance between samples.
Disclaimer to the disclaimers - at the group buy pricing, there's no tears to shed if you burn out one or a handful experimenting with something interesting. These are great to learn with.
Method
Power was controlled by a linear power supply. An inline shunt resistor was used to derive current from voltage drop over the resistor. Voltage was increased on the power supply until the expected voltage for each current level was achieved. The multimeter was then moved to measure forward voltage of the LED, and resistance of the photocell. Separate data were taken approximately correlating photocell resistance with luminous intensity. Checks made on that data showed fair agreement with expected values.
Results
In a dark room, a faint glow was perceptible starting around 2.35V, at microamps of current. Measurements started at 2.53V and roughly 0.2mA. This batch of LED's is rated for a forward voltage of 2.8-2.9V at 20mA. This sample tested at 2.81V at 20mA.
Light output peaked at 90mA and 3.23V. Output appeared stable, and tint minimally less warm than at lower currents. A pink tint becomes noticeable around 110mA, increasing to dominate the tint as current rises. Current ceased to be stable with respect to voltage at 3.49V and initially at 160mA. No more measurements were taken, and voltage was increased over the space of a few seconds until the LED went completely dark at about 200mA.
After a short rest, the LED was powered on again at 20mA. The LED was clearly seriously damaged. Brightness was roughly equivalent to the previously measured 5mA level, and the forward voltage necessary to achieve 20mA seemed to have risen to 4.4V.
Graph and images follow. 4500K camera white balance was chosen to approximate naked eye appearance.
Standard rated current of 20mA, before and after overload test:
The full test was photographed at fixed camera settings (1/20s, F/10, ISO200, 4500K WB). The following image should display as an animated GIF:
Intro
With literally several thousand of these emitters now in circulation among CPF members, I thought it was worth taking some data on their performance when overdriven.
Before continuing, I want to thank those who have organized group buys or even outright shared Yuji 5mm emitters with others, including scout24, ma tumba, lampeDépêche, and K2-bk-bl-rd. This is part of what makes CPF a great community!
Disclaimers
1.) Treat my data as approximate, primarily for comparison to itself. I used a cheap, salvaged photocell I came up with my own rough calibration method for. My budget solderless breadboard also clearly had intermittent contact issues from handling that caused small fluctuations in some of the data. I'd be surprised if voltage and current measurements were off by more than 5%, but I'd be happy if I were able to confirm my Candela data are within +/- 50%.
2.) Anything above 30mA exceeds manufacturer specs. Worsening life span (potentially both hours and on/off cycles) should be expected the higher the currents go, but I have no data on how much worse. My testing lasted maybe 4-5 minutes at each current level as I moved my multimeter between measurement points, waited for stable readings, and recorded data.
3.) I tested a single sample. There may be variation in performance between samples.
Disclaimer to the disclaimers - at the group buy pricing, there's no tears to shed if you burn out one or a handful experimenting with something interesting. These are great to learn with.
Method
Power was controlled by a linear power supply. An inline shunt resistor was used to derive current from voltage drop over the resistor. Voltage was increased on the power supply until the expected voltage for each current level was achieved. The multimeter was then moved to measure forward voltage of the LED, and resistance of the photocell. Separate data were taken approximately correlating photocell resistance with luminous intensity. Checks made on that data showed fair agreement with expected values.
Results
In a dark room, a faint glow was perceptible starting around 2.35V, at microamps of current. Measurements started at 2.53V and roughly 0.2mA. This batch of LED's is rated for a forward voltage of 2.8-2.9V at 20mA. This sample tested at 2.81V at 20mA.
Light output peaked at 90mA and 3.23V. Output appeared stable, and tint minimally less warm than at lower currents. A pink tint becomes noticeable around 110mA, increasing to dominate the tint as current rises. Current ceased to be stable with respect to voltage at 3.49V and initially at 160mA. No more measurements were taken, and voltage was increased over the space of a few seconds until the LED went completely dark at about 200mA.
After a short rest, the LED was powered on again at 20mA. The LED was clearly seriously damaged. Brightness was roughly equivalent to the previously measured 5mA level, and the forward voltage necessary to achieve 20mA seemed to have risen to 4.4V.
Graph and images follow. 4500K camera white balance was chosen to approximate naked eye appearance.
Standard rated current of 20mA, before and after overload test:
The full test was photographed at fixed camera settings (1/20s, F/10, ISO200, 4500K WB). The following image should display as an animated GIF:
Last edited: