Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Neutral white, Utilizes four Cree XP-G2 neutral white LEDs, max 1600lumens output, Powered by four BAK 18650
Aliexpress
I could not find it on Aliexpress. Click here to search by yourself.
Here are coupons that you can use.
Latest price update (UTC time):
Price history and price alert
Here is price history (for all/most countries) for Nitefighter BT40S Bicycle Light.
Price records source(s): Gearbest
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).