About CD intensity, Beam distance, and blinding

RemcoM · Jun 29, 2013

Hi everyone,

How bright do i flashlight need to be, when it start begin annoying/blinding for others, if shine straight forward ,mounted on a bicycle?

For example, If mounted the Fenix TK 75 on a bicycle.

1 What about, when you drive with the low setting of 18 lumens, 60 meters beam distance, and around 800 CD or so, (shining straight forward)

2 And how will it be for oncomming traffic, when the light on a bicycle (shining straight forward) is at mid mode, 400 lumens, 230meters beam distance, 13000 CD intensity?

3 And how will it be, for oncomming traffic, when the light is at high mode, 1100 lumens, 350 meters beam distance, 35000 CD intensity?

4 And what about, driving around, with turbo setting, 2600 lumens, 606 meters beam distance, 92000 CD intensity, shining also straight forward?

This questions are just for interest, and NO ,im not try this out. Only curious, how it will be for oncomming traffic.

Remco

kj2 · Jun 29, 2013

You could test it yourself

Mount the light on your bike, select the mode you want, walk 10-20meters in front of your bike and turn around.

kamote-fries · Jun 30, 2013

Even at 18 lumens it'll be annoying especially for a reflectored light. I tried several ways on how to hold a light while walking and when I switched to an underhand grip, some drivers got annoyed and kept flashing at me. I was using my light at 10 lumens. The spill produces a lot of glare and this would annoy drivers and pedestrians coming your way.

RemcoM · Sep 12, 2013

Only one question, i just want know.

1 Does a 60000 cd candela flashlight outthrow a headlight of a scooter/motorbike, where young people always drive with?

Remco

wjv · Sep 12, 2013

Sounds like the Fenix TK 75 is not the right choice for a bike light.

Seems like something more floody would be what you would want,

RemcoM · Sep 13, 2013

I think, 60000 cd candlepower is blinding for oncomming traffic, am i right?

But what about the cd number of scootersheadlights, where young people always drive with?

Have somebody a guess?

Remco

RemcoM · Sep 14, 2013

Please reply to my post ,last post above.

Thank you.

davyro · Sep 14, 2013

It's simple really just dip your flashlight like cars or motorbikes then you won't be shining a light straight into there eyes because the light is angled downwards

RemcoM · Sep 15, 2013

But Headlights of motorbikes, are mostly shining straight forward i see many times. Why is that?

And is a light that shines with 60000 Cd candlepower dangerously bright, when shining straight forward?

Etsu · Sep 15, 2013

Direct mid-day sunlight is about 10000 foot-candles, so 60000 candles would certainly be extremely dangerous. However, it's very unlikely that the beam has an intensity of 60000 candles by the time it reaches an oncoming driver. It might have that intensity a few inches away, but not several dozen yards away. I'm not sure what kind of light would have an intensity of 60000 candles at any distance, but perhaps a high-powered laser or a massive search-light or something? I guess a laser might maintain high intensity for quite some distance.

That said, even a lower intensity light might still be dangerous. An oncoming driver may be so annoyed at you shining a bright light at him, that he deliberately runs you over in a fit of road rage.

1nterceptor · Sep 15, 2013

If you mount a light on your helmet, you'll have more control of the
beam's direction. Although a TK75 might be too heavy for helmet
mounting. In this video, I tried both helmet and bar mounting.

http://www.youtube.com/watch?v=RFxCXb7Ju38

AnAppleSnail · Sep 15, 2013

RemcoM said:
But Headlights of motorbikes, are mostly shining straight forward i see many times. Why is that?

And is a light that shines with 60000 Cd candlepower dangerously bright, when shining straight forward?

Different beam pattern. Shine a flashlight and a headlight on a wall to see. Simple brightness is not the goal of headlamp design, and absolute brightness (Over all other considerations) is very dangerous on the road.

TEEJ · Sep 15, 2013

AnAppleSnail said:
Different beam pattern. Shine a flashlight and a headlight on a wall to see. Simple brightness is not the goal of headlamp design, and absolute brightness (Over all other considerations) is very dangerous on the road.

I was about to say this essentially.

A vehicle head light casts a pattern of light with an upper cut off, more of a rectangular beam pattern...TO help avoid glare to those facing it.

A FLASHLIGHT casts a ROUND beam, with no upper cut off, or even an up/down orientation.

That means that a vehicle's beam concentrates its light at the ground, with very little sent skyward. A Flashlight's beam doesn't proportion the light at all, it's brighter in the middle and gets dimmer to the outer edges.

That means that if you are in front of a vehicle's headlights, the beam is cast so as to be on the ground/your waist perhaps, but not at your eyes...and if the light has 600 lumen, ~ most of the 600 L are sent at the road.

In front of a flashlight, even if aimed to center on the ground a distance ahead of you, the upper part of that round beam is still higher, and likely in the eyes of those in front of it.

This is WHY a flashlight is a TERRIBLE vehicle light....its got the wrong beam pattern....and MOST of the light cast is wasted on air/sky you didn't need to see/the eyes of those you didn't want to blind, etc....and LESS is available to actually see where you're going.

Does that make sense?

--------------------------------------------------

As for the cd...its being mis-used in this context.

cd MEANS the LUX at one meter...the cd IS the Lux at 1 meter.

IE: How bright it is at that range.....and, because light intensity falls off at a predictable rate following the inverse square law...it's essentially a 1/4 as bright at double the distance.

So if a light is rated at 60,000 cd, that means it's putting 60,000 lux on a target at a range of 1 meter....and, for perspective, about 17 LUX at 60 meters, about 1 at 230 meters, and about 0.5 at 350 meters, and so forth.

IE: Its not putting out a different cd at different distances, its putting out different LUX at different distances. (But KNOWING the cd allows you to calculate the lux at any distance)

Lurveleven · Sep 16, 2013

When biking in traffic, you should use a light designed for bike use, like Fenix BT20, so you don't blind others. The BT20 cuts off the upward part of the beam. When biking offroad it is probably better to use an ordinary type of beam that let you see branches above your head.

RemcoM · Sep 16, 2013

TEEJ said:
I was about to say this essentially.

A vehicle head light casts a pattern of light with an upper cut off, more of a rectangular beam pattern...TO help avoid glare to those facing it.

A FLASHLIGHT casts a ROUND beam, with no upper cut off, or even an up/down orientation.

That means that a vehicle's beam concentrates its light at the ground, with very little sent skyward. A Flashlight's beam doesn't proportion the light at all, it's brighter in the middle and gets dimmer to the outer edges.

That means that if you are in front of a vehicle's headlights, the beam is cast so as to be on the ground/your waist perhaps, but not at your eyes...and if the light has 600 lumen, ~ most of the 600 L are sent at the road.

In front of a flashlight, even if aimed to center on the ground a distance ahead of you, the upper part of that round beam is still higher, and likely in the eyes of those in front of it.

This is WHY a flashlight is a TERRIBLE vehicle light....its got the wrong beam pattern....and MOST of the light cast is wasted on air/sky you didn't need to see/the eyes of those you didn't want to blind, etc....and LESS is available to actually see where you're going.

Does that make sense?

--------------------------------------------------

As for the cd...its being mis-used in this context.

cd MEANS the LUX at one meter...the cd IS the Lux at 1 meter.

IE: How bright it is at that range.....and, because light intensity falls off at a predictable rate following the inverse square law...it's essentially a 1/4 as bright at double the distance.

So if a light is rated at 60,000 cd, that means it's putting 60,000 lux on a target at a range of 1 meter....and, for perspective, about 17 LUX at 60 meters, about 1 at 230 meters, and about 0.5 at 350 meters, and so forth.

IE: Its not putting out a different cd at different distances, its putting out different LUX at different distances. (But KNOWING the cd allows you to calculate the lux at any distance)

Thank you for your help.

So i can expect, that the headlight of a scooter,where young people drive with, is not having 60000 cd candlepower? Thats 500plus meter beam distance.

How much Cd do you think/expect, that a scooter/motorbikeheadlight has?

Etsu · Sep 16, 2013

Oops, sorry, I thought you meant foot-candles, but it's candlepower. In that case, yeah, I don't see that 60,000 candlepower is unreasonable for a headlight.

RemcoM · Sep 19, 2013

Hi, Teej, and others.

Again, some questions.

1 How bright does my Fenix TK75 2600 lumens at turbo setting, almost 700 meters beam distance, over 100000 cd (mine is very overpowered)lucky me, will look in the darkness ,outside a city, when somebody is shining it at me from 2000 meters/2 kilometres? How much lux do it has from that distance? Are objects a very little illuminated? Do i see a bright light then from that distance? Can i clearly see it then?

A friend of me,and i, are go test this, when he is back from holiday, in 3 weeks, so i ask it here, because im very bad in imagine, and calculate things.

2 And how will my Fenix EO1 18 lumens, 20 meters beamdistance, will look from 2000 meters/2 kilometres distance? When my friend shines it at me from that distance? Do i see it then clearly also?

And how much lux will the Fenix EO1 produce at 2000 meters/2 kilometres distance?

TEEJ · Sep 19, 2013

RemcoM said:
Hi, Teej, and others.

Again, some questions.

1 How bright does my Fenix TK75 2600 lumens at turbo setting, almost 700 meters beam distance, over 100000 cd (mine is very overpowered)lucky me, will look in the darkness ,outside a city, when somebody is shining it at me from 2000 meters/2 kilometres? How much lux do it has from that distance? Are objects a very little illuminated? Do i see a bright light then from that distance? Can i clearly see it then?

A friend of me,and i, are go test this, when he is back from holiday, in 3 weeks, so i ask it here, because im very bad in imagine, and calculate things.

At 2,000 meters, shined TO you, a 100,000 cd light will produce only 0.025 lux....IE: YOU might see the beam off in the distance, but you would be invisible to the one WITH the light. You'd see the beam as a light, off in the distance.

2 And how will my Fenix EO1 18 lumens, 20 meters beamdistance, will look from 2000 meters/2 kilometres distance? When my friend shines it at me from that distance? Do i see it then clearly also?

And how much lux will the Fenix EO1 produce at 2000 meters/2 kilometres distance?

I don't know if you'd be able to see it or not, it would be a very small point of light if you did, and the light REACHING you would be so small that you'd not have any illumination.

Etsu · Sep 19, 2013

In a very dark sky, you can see stars down to 6th magnitude or even slightly dimmer. That's only 0.00000001 lux falling on you from a star that dim. Granted, it's a point source, so the light is concentrated into that small point. But a Fenix E01 at 2km distance would look like a point too. I'm pretty sure it would provide more lux than 0.00000001 on a target 2km away, so you'd be easily able to see it if it was dark enough and you were looking towards it.

AnAppleSnail · Sep 19, 2013

Let's do the math. An E01 gives 110 lux (At 1 meter). At twice that distance, (Double height and double width) 4x the area is lit, so the lux is 27.5 at 2 meters. Another doubling, 4 meters, the lux is a fourth again, 6.875 lux. In short, we have about the same intensity as a 5th or 6th magnitude star.

Lux	Distance
110.00000	1
27.50000	2
6.87500	4
1.71875	8
0.42969	16
0.10742	32
0.02686	64
0.00671	128
0.00168	256
0.00042	512
0.00010	1024
0.00003	2048

It's usually very hard to see 5th magnitude anywhere near or below the horizon because of other light sources.

About CD intensity, Beam distance, and blinding

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