Changing Leds on sequential shift light

Thread Starter

mrguibo

Joined Mar 7, 2023
3
Hi all, so my motorcycle (2013 triumph street triple 675) has a sequential shift lights on top of the speedo. The leds light up according to rpm and then flash at redline. It is made of 6 through hole blue leds and I want to change the leds to a gradient from yellow to red. So wavelength 590, 600, 610, 620, 630, 640. Aside from creating a breadboard to test, is there a way to figure out the brightness looking at specs and ensure all 6 leds have the same brightness?
Thanks!
 

Audioguru again

Joined Oct 21, 2019
6,647
Don't you want the LEDs to be bright in sunlight but be dimmed at night? Dim then when the other lights are turned on at night.
LED brightness is different for different colors and each LED will have its own brightness even if they have the same color and part number.

Watch out for the "beam angle". A narrow angle is focused straight ahead and is very bright only when it shines directly in your eyes but a wide angle is what you want.
 

bradrs

Joined Jan 23, 2023
17
Some datasheets will have a luminous intensity vs forward current. Depending on the PCB, there may be external resistors that limit current through each individual LED, to get the target brightness.

The warning about beam angle is important to keep in mind. I put LEDs on a motorcycle dash a long time ago, and had to look around for wide angle LEDs to get it to be more useful, and not just blind you at a certain angle.


Don't you want the LEDs to be bright in sunlight but be dimmed at night? Dim then when the other lights are turned on at night.
If it is in the USA, the lights have come on with the ignition switch since the 70s I think. No headlight switch or dimmer on the dash lights. Other countries do have on/off switches for the headlights. But I don't think they do anything different with dash lighting, I think everyone just has it on all the time.
 

Thread Starter

mrguibo

Joined Mar 7, 2023
3
Good point about the view angle. The leds are housed in a plastic thing that surrounds the sides so I was shooting for a 30* view angle. And ya my bike always has its lights on. For the luminous intensity, does that differ for different wavelengths (ie have to get a brighter led for 640nm)?
 

MisterBill2

Joined Jan 23, 2018
18,061
Apparent luminous intensity does vary with wavelength/color.Also the LED forward voltage varies with colors, while the actual intensity varies with current. So if all of the blue LEDs are the same intensity, and each of them has an individual resistor, then the different colors will vary in intensity if no changes are made. But probably the red will be the very brightest because red LEDs have the lowest forward voltage. Green would have the lowest because it has the highest forward voltage of the three colors.
But if all of the LEDs are fed directly from an IC that has a single resistor to set the forward current of all the display then more work will be required.
 

Jon Chandler

Joined Jun 12, 2008
1,024
The LEDs you need are called "diffused" – the case of the LED is colored and looks frosted. LEDs with a "water clear" case produce a narrow cone of light that will leave spots in your eyes if viewed directly.
 

MisterBill2

Joined Jan 23, 2018
18,061
I suggest taking a look inside and seeing what is driving those LEDs. If it is some version of a chip similar to the LM3914 then there is a single constant current driver for each LED output and setting the current for different LEDs will be more complicated.
 

DickCappels

Joined Aug 21, 2008
10,140
The only practical way to match the apparent brightness is to test the LEDs with the intended background and the intended incident illumination. Only then can you adjust the current and try to get them to match.
 
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