I don't know that for sure but 630nm is much more common. Look at the wavelength column here, it's all ~630nm: https://www.digikey.com/en/products/filter/led-i

I don't know that for sure but 630nm is much more common. Look at the wavelength column here, it's all ~630nm: https://www.digikey.com/en/products/filter/led-indication-discrete/105?s=N4IgTCBcDaIE4FMAmACANskBdAvkA https://www.digikey.com/en/products/filter/led-indication-di... Given that I'd be very surprised if my crappy little head torch is 670nm. If you can use a soldering iron I think it would be relatively straightforward to modify an off-the-shelf headlamp and swap out the diode. https://www.digikey.com/en/products/filter/led-indication-discrete/105?s=N4IgjCBcoMwOxVAYygMwIYBsDOBTANCAPZQDaIMAnAKwBMYlIAuoQA4AuUIAyuwE4BLAHYBzEAF9CANkbQQKSBhwFiZEABYwYAByUELEBy69BoiYUpTtieWix5CJSOVpTqu6waOQe-YWPFJEFo1PlwAEwACTAjmcSA https://www.digikey.com/en/products/filter/led-indication-di...