why do things reflect more with led lights

c670809 · Apr 6, 2008

I was wondering why led lights seem to make things reflect more and farther than incandescents.

I notice with my led bike lights that license plates, road signs, and reflectors literally LIGHT up from a huge distance away. I don't notice the same effect with any incandescents. My led headlamp makes signs light up WAY more then even my car.

Is it the wavelength, color temperature or something else???

Thanks for your thoughts.
Matt

hopkins · Apr 7, 2008

somewhen I saw them making street signs. They mixed a special reflective
particle into the paint and them dusted the painted surface with more of it.
I've noticed that effect also. You don't think the led beam is reaching that far
but then the street sign gives a reflection.
Anyway instead of getting all scientific its more fun to say led's are magic !

c670809 · Apr 7, 2008

I'm glad I'm not the only one who's noticed this.

Thanks for responding.

WadeF · Apr 7, 2008

Seem to have the same effect on animal's eyes, like deer.

TigerhawkT3 · Apr 7, 2008

WadeF said:
Seem to have the same effect on animal's eyes, like deer.

I've seen that on some of the CPF night hikes. Most of us walk around spotting things with our LED throwers, and every now and then someone will pick out a pair of glowing eyes. Then, after they let everyone know, I (or someone else with a similar light) will blast the area with >100W of hotwire goodness, and we'll actually SEE the deer, plus its buddies and most of their surrounding environment. I can't wait until LEDs get there...

I can't say that I've noticed a difference in reflectivity of LED vs incan beams, but I haven't been looking for one, either. I'll be sure to check it out.

pbs357 · Apr 7, 2008

I don't know the answer either, but my experience is the same. At distances that it seems the beam isn't capable of lighting, a reflector or road sign will brightly "light up" when shined by an LED thrower. Yeah, must be magic LOL.

TONY M · Apr 7, 2008

A friend on mine went to the amazon last year. He said that even though his LED light was brighter than the guides cheap 2aa incans it did not show up animals eye's in the dark at all well and he wished he had brought an incan with him.

It is just what he said and it seemed interesting but I haven't done any sort of comparison myself.

Justin Case · Apr 7, 2008

The phenomenon you are seeing is called retroreflection, where the reflected light comes straight back to the source (concentrated in a narrow cone). Basically, the more light that is sent to the retroreflector (for some given entrance angle), the more light that will come back (for some given observation angle). Most likely, the LED lights have better throw than the incandescents, and are also brighter to begin with. So, it isn't a surprise that the retroreflection return is also stronger.

cave dave · Apr 7, 2008

I think color temp has something to do with perceived brightness.

You also mention using a headlamp.

The closer your eyes are to the source the more light will be bounced back. So a headlamp will always bounce back more light than an equivelent handheld. Try moving a handheld from your waist up to your forehead as you beam a distant sign.

Citivolus · Apr 7, 2008

The light curve of white LEDs is very high in blue due to their design, which could result in the perceived brighter/hotter reflections. Incandescents will be shifted into the Red/IR portion of the spectrum, resulting in them being perceived as dimmer.

saabluster · Apr 8, 2008

TigerhawkT3 said:
I can't wait until LEDs get there...

I'm working on it now.:naughty: :sssh:

adamlau · Apr 8, 2008

Additonal glare induced by the blue light spectrum is what you are perceiving as increased reflection.

LedSanders · Apr 8, 2008

TONY M said:
A friend on mine went to the amazon last year. He said that even though his LED light was brighter than the guides cheap 2aa incans it did not show up animals eye's in the dark at all well and he wished he had brought an incan with him.

It is just what he said and it seemed interesting but I haven't done any sort of comparison myself.

I have a Fenix T1 and it lights the eyes of animals much brighter than my 3D Mag.
i.e. Deer, Rabbits, Cats, Dogs, Chupacabra, Sasquatch, and the other unknowns I have seen around my home in AZ

NA8 · Apr 8, 2008

I've noticed street signs light up brightly even though it's only the light's spill that's hitting the signs. The hot spot is down the street in the center somewhere. Impressive technology.

bobofish · Apr 8, 2008

This could be complete bunk, but I remember reading somewhere that LED's mostly shoot their light straight out of the emitter even when they have a reflector, as opposed to incan's that create a "globe" of light that needs a reflector to reach its target. I would assume then that the LED rays are more "in line" and therefore can bounce back to the source easier.

But the whole blue spectrum thing is probably more of a factor anyway.

Torque1st · Apr 8, 2008

With a few simple tests around the house here animal eyes seem to reflect stronger with different beams because they reflect different colors. Red eyes reflect stronger with an incandescent. Blue or green eyes seem to reflect stronger with an LED. Take this for what it cost you. The test was extremely unscientific. Getting the various animals to look in my direction while I shined a light at them was difficult. Animals are much smarter than humans.

LEDs are surface emitters and are usually very directional which is why lenses work better than reflectors. There are some interesting packages that throw light in different directions however. :thumbsup:

TorchBoy · Apr 8, 2008

LedSanders said:
and the other unknowns I have seen around my home in AZ

I took a look at those unknowns, and recognised one. You've seen wumps (capybaras) around your home?

Has anyone noticed how well LED light reflects from the red part of retroreflective signs compared to the white part?

selfbuilt · Apr 8, 2008

TONY M said:
A friend on mine went to the amazon last year. He said that even though his LED light was brighter than the guides cheap 2aa incans it did not show up animals eye's in the dark at all well and he wished he had brought an incan with him.

I heard the same comment made by the guides on my costa rican wilderness trip last year. However, my 1st gen D-mini (on low) did a far better job of catching animal eyeflashes than other people's incan lights, including 2D mags.

Do you know what he was carrying? I suspect the problem is early LED lights that had poor throw (especially multi-LED setups), leading to a general perception that they were worse than incans for eyeflashes.

Of course, the other issue is identifying species by the color of their eyeshine. I could see here how incans could have an advantage over the narrower spectrum of LEDs. But I didn't have enough direct field testing to be able to comment on that (and didn't have an incan with me to compare).

Jarl · Apr 8, 2008

Citivolus said:
The light curve of white LEDs is very high in blue due to their design, which could result in the perceived brighter/hotter reflections. Incandescents will be shifted into the Red/IR portion of the spectrum, resulting in them being perceived as dimmer.

Red shift occurs when stuff is travelling away from you/you're travelling away from the stuff. Also, the light that was UV pre-shift, is blue after the shift, just as the blue light pre-shift is red after the shift (simplified!), so there's no visual difference.

TONY M · Apr 8, 2008

selfbuilt said:
I heard the same comment made by the guides on my costa rican wilderness trip last year. However, my 1st gen D-mini (on low) did a far better job of catching animal eyeflashes than other people's incan lights, including 2D mags.

Do you know what he was carrying? I suspect the problem is early LED lights that had poor throw (especially multi-LED setups), leading to a general perception that they were worse than incans for eyeflashes.

Of course, the other issue is identifying species by the color of their eyeshine. I could see here how incans could have an advantage over the narrower spectrum of LEDs. But I didn't have enough direct field testing to be able to comment on that (and didn't have an incan with me to compare).

SB. I have no idea what light he was using but he was most insistant that it was something to do with the LED itself. However I would not be surprised if it was due to poor throw or even perhaps far more likely an "operator error." That was a while back now. Last night I did a quick comparison at range with a few lights on my dogs eyes

(no matter how hard I pleaded the girlfriend would take no part in it :thumbsdow) and the brighter lights were better as you would expect - regardless of being LED's or incans.

why do things reflect more with led lights

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