I have a D 140 and it's fine for night use. It's visible in daylight, but you're fighting a losing battle against all the light from Mr. Sun.

If I were expressly looking for a day-use taillight and had the funds, I'd spring for the "double 140", the 400 2-led model, IIRC. That's your best chance of being seen. Supplement with a helluvalot of hi-vis yellow/green apparel/bags etc.