build pure orange light

660 nM is deep red actually - I assume you're thinking along the lines of a lamp to help sleep and such? Or is this for chickens (I used to keep them as pets and a study aid for avian behaviour, fascinating animals).

But you're in luck, that wavelength is specifically produced for the poultry industry so they are readily available.

https://www.moon-leds.com/product-660nm-deep-red-3w-power-led.html

The alternative (not so great) solution would be to use something like the WS212B which is a very popular multi-colour LED with it's own chip, so they pop up on bargraphs and such. I suspect you'd have trouble calibrating those to pure deep orange/red (sunset/sunrise).

Remember that the larger LEDs usually need to be mounted on a aluminium board to sink the heat they generate.

You'll also need to consider the power implications of driving these beasts. This particular example needs about 2.5 volts at almost half an amp for between 20 and 30 lumens - not a lot compared to a 60W incandescent bulb which is around 800 lumens (30 - 40x brighter) so for you're going to need quite a few and a clear diffuser to scatter the light.

@marcdraco 

I could be wrong, but afaik does an LED only operate at a very narrow wavelength. The Red-LED of the WS2812B is right around 625nm according to the datasheet. Mixing a bit of Blue and Green into that won't "shift" the wavelength to 660nm, but instead trick our eyes into seeing the light as if it were 660nm. 

So if the specific wavelength is important to this project, maybe an LED thats specifically tuned to that wavelength would be a better option?

Exactly Sam, I've mentioned that in the post (see the link). I kept chickens for a few years myself until my new landlord declared they had to go. Miserable SOB. Anyways, chickens have a circadian rhythm that can be adjusted using (drum-roll) 660nM narrow spectrum radiation, essentially a laser diode but not focused into a coherent, collimated beam. (I'm actually playing with the cat using such an item now, he won't let me work so I have to tire him out.)