Dear Glen,
Please check this thread if you want to take a look at Sofirn's C01R:
https://budgetlightforum.com/t/-/58847
It uses Cree's XP-E2 photo red (660nm dominant wavelength). Certainly, this light is not meant for shining into anyone's eyes but with some minor changes (wide angle beam, frosted/diffused optic and a lower low-mode) it might be useful for scientific/medical purposes as well. Would be interested in testing one? I will be glad to establish communication with Sofirn (the manufacturer).
If you have any good hints where to get 670nm LEDs, I would be more than happy to know about them. The only deeper "tint" available that I know about is far red with 710-730nm. However, this wavelength seems borderline already in terms of visibility, being so close to the infrared spectrum.
Thanks a lot for being here and sharing your ideas!
Cheers,
Thomas