[copperx]

I do not understand the assumptions behind this question. Can you clarify what you mean?

[baq]

Is a red bulb enough or do you need a 670nm laser?

[tlrobinson]

I hope this was a joke. Don’t shine lasers in your eyes. https://en.wikipedia.org/wiki/Laser_safety

[flyinglizard]

For the love of all that’s dear in this world, please don’t use a laser for that.

If you’re in a DIY mood, you can easily pick LEDs around that wavelength and they would generate more than enough light to even cause damage (if close enough).

[andrew_]

what assumptions? it was an honest question.