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  1. #1
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    Watts, Lumens and the Law

    My locale has a law requiring bike lights to be at least 1 Watt. Kinda silly language because it doesn't really measure something relevant to what I presume their intent was. I'm using one of the lower end DX Extreme Cree flashlights (~90 lumens) but I haven't a clue as to its wattage. I highly doubt I'll ever be challenged on this but, inquiring minds wanna know; how do I figure the watts?

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    Senior Member socalrider's Avatar
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    your fine, a 1 watt luxeon will top out at 40-50 lumens..

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    This steel horse I ride Skones MickLoud's Avatar
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    Lumens can't convert to wattage, as they measure completely different things. A 1 watt bulb could put out more lumens than a 100 w bulb, and vise versa. Best thing to do would be to open the case (if possible) and look at the bulb, which should have a wattage rating on it.
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    Quote Originally Posted by Skones MickLoud View Post
    Lumens can't convert to wattage, as they measure completely different things.
    Well... no, they are not completely different things. The lumen is a measure of light energy flux*, and watt here refers to electrical energy flux. Electrical watts going in, multiplied by an efficiency coefficient (always < 1) equals light energy out. Different lighting technologies have different ranges of efficiencies, so it is possible to say, for example, that "A white LED typically produces between 20-60 lumens per watt input of electrical energy." See http://www.mge.com/home/appliances/l...comparison.htm

    *This is not exactly true - the lumen is color weighted for human vision perception - but it's close enough to true for this argument about light-producing devices for human vision enhancement.

    Here's another approach. Capacity / runtime = amps. Amps x volts = watts. What's the claimed runtime? What's the battery pack made of? Example: 2.5 Ah battery / 2.5 hours runtime = 1 amp. 2.4 volts x 1 amp = 2.4 watts.
    Last edited by duffer1960; 10-04-09 at 04:51 AM.

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    That's about as unenforceable of a law as I've ever heard about. A 1 Watt source can emitt different lumens as just mentioned. A 1 Watt laser will burn holes in wood and set many things on fire. I'm pretty sure you can buy a 0.5 Watt laser that's handheld with a battery in the case like a flashlight. A 1 Watt incandescent source is not even a good nightlight.

    Also depends on the optics in front of the light. A 1 Watt LED source without optics emitts in essentially a half dome. Very dim. Put a lens or reflector in front of it and you have a useable beam. Focus it too much and only a tiny spot on the road will be illuminated, and there will be no light emitted off to the sides at all for visibility to drivers.

    The OP should work to elect smarter representatives in his locale!

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Skones MickLoud View Post
    Lumens can't convert to wattage, as they measure completely different things. A 1 watt bulb could put out more lumens than a 100 w bulb, and vise versa. Best thing to do would be to open the case (if possible) and look at the bulb, which should have a wattage rating on it.
    Not necessarily. The radiant flux of a light is measure in Watts or the radiant energy per unit time. This is the definition of a watt, i.e energy per time. A lumen is the luminous flux of the light source. It takes into account only the light that our human eyes can perceive. We can't see into the IR (below red on the spectrum) or into the UV (above violet on the spectrum). In the radiant flux measurement those are taken into account.

    However, I would suspect that the city council that wastan isn't that sophisticated in their definitions. From a practical stand point, a 1W incandescent light is probably in the 12 to 15 lumen range. Get an old incandescent pen light like this



    and you'll probably be 2 watts over the 1 watt minimum or at about 45 lumens.

    Definitely not sufficient for night riding 90 lumens is hardly sufficient. More is always better
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    More isn't better from the oncomming drivers' and cyclists' perspective. Too bright of a light from a tiny little source like an LED is dangerously distracting, and can very possibly cause temporary blindness in the center of the field of view. That's why it's against the law to not dim your headlights for oncomming traffic. THAT's a good law!

    Too much light can be a weapon. Shining too much light into the face of a nighttime driver is dangerous for EVERYONE on the road then, and for quite a while after the encounter. Do YOU want a temporarily blinded driver comming up behind YOU?

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by RapidRobert View Post
    More isn't better from the oncomming drivers' and cyclists' perspective. Too bright of a light from a tiny little source like an LED is dangerously distracting, and can very possibly cause temporary blindness in the center of the field of view. That's why it's against the law to not dim your headlights for oncomming traffic. THAT's a good law!

    Too much light can be a weapon. Shining too much light into the face of a nighttime driver is dangerous for EVERYONE on the road then, and for quite a while after the encounter. Do YOU want a temporarily blinded driver comming up behind YOU?
    If we cyclist rode our bikes near the yellow line, you might have an argument. However, most of the time we are to the right of the right wheel track of automobiles on the road. If you haven't noticed, the right light on cars is aimed further down the road than the left. It would be difficult to shine the light from my lights...even if they were aimed very high, which they aren't...into the eyes of oncoming traffic. Even a very wide beam, like a 35 degree flood, wouldn't shine in the eyes of a car that is...or should be...11 to 15+ feet away from me.

    Cars are also pumping out 1500 lumens...on dim...per lamp! It's tough to get that kind of firepower. Even if you can (and I do), the other cars on the road are used to that amount of light. And the drivers are closer to the light from other cars than I will be to an oncoming car. They aren't blinded by those are they?
    Last edited by cyccommute; 10-04-09 at 10:21 AM.
    Stuart Black
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    Car headlights are typically large sources. Tiny sources like bike light LEDs produce much higher energy density on the retina for the same intensity. Also car headlights spread their lumens out over a much wider area than bike headlights.

    Even though a bike headlight is pointed down toward the road, it's not necessarily there when you stop. All you have to do is tilt the bike a tiny little bit, like at a stop light, and when the front wheel turns a bit the light is directed full force into the eyes of drivers waiting at the light across the intersection. Same situation when the bike banks around curves or to avoid road hazards.

    Then there's the situation of cyclists mounting strong LED lights on their helmets, a very unsafe and foolish thing to do when riding on the road. Everything they look toward gets the full beam in the face. Maybe OK on a trail, but definately NOT on the road.

    People take light for granted. Flash yourself at night with your headlight and then tell me how benign it is.

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by RapidRobert View Post
    Car headlights are typically large sources. Tiny sources like bike light LEDs produce much higher energy density on the retina for the same intensity. Also car headlights spread their lumens out over a much wider area than bike headlights.
    Car lights are large sources but they are also from <3 feet to 8 feet away from on-coming traffic. Bicycle lights are at a minimum of 10 feet to more then 15 feet away. Since beam spread goes up with increasing distance and intensity goes down with increasing distance (usually by some power function), the intensity reaching the other lane is greatly diminished. You'd have to have a light that has much more luminous flux than a car light to cause problems for oncoming traffic from that distance. The distance is why bike lights are so hard to see against other light sources. And most bike lights don't have that high a luminosity to begin with.

    Quote Originally Posted by RapidRobert View Post
    Even though a bike headlight is pointed down toward the road, it's not necessarily there when you stop. All you have to do is tilt the bike a tiny little bit, like at a stop light, and when the front wheel turns a bit the light is directed full force into the eyes of drivers waiting at the light across the intersection. Same situation when the bike banks around curves or to avoid road hazards.
    Again, distance. When you stop...usually an intersection...the oncoming traffic is at least 2 lanes away from your light source. That's 22 feet to 60 or 70 feet, depending on the width of the intersection. Even a highly concentrated source is going to spread significantly in that distance. A laser beam would spread significantly in that distance and they are much more highly focused than a bike light

    On curves, the light from a handlebar mounted lamp goes off in a straight line from the light. On the outside of a curve, the light is going to spray off into space and not affect oncoming traffic. On the inside of the curve, the amount of time that the light could shine in oncoming traffics' eyes is momentary at best because of the speed differential in the corner. The bike is also going to be leaning into the corner which directs the beam towards the inside of the curve. And, again, the light is going to be rather far away from the eyes of the oncoming driver. Another motorist is going to be much closer than a bike would ever be.

    Quote Originally Posted by RapidRobert View Post
    Then there's the situation of cyclists mounting strong LED lights on their helmets, a very unsafe and foolish thing to do when riding on the road. Everything they look toward gets the full beam in the face. Maybe OK on a trail, but definately NOT on the road.
    Mounting a helmet light is not unsafe nor foolish nor even that dangerous. Yes, you should be courteous to other road users. Most people know that...we aren't entirely stupid Used properly, it's just another tool for making sure you are seen. It also increases the ability to see what is in a corner because your eyes don't follow the lean of the bike in a corner. Without a helmet light, corners are very dark and can hide all kinds of holes and possible crash inducements. Crashing at night is far more dangerous than crashing in daylight.

    Quote Originally Posted by RapidRobert View Post
    People take light for granted. Flash yourself at night with your headlight and then tell me how benign it is.
    At what distance? Arms length? You'd never find that condition on a road way. Not unless you are intentionally trying to blind a driver.

    At more realistic distances? I doubt you'd notice it more than a car's headlamps which we deal with every time we ride, or drive, at night.

    I agree that people take light for granted. Often too so much because they run lights on their bikes that are ineffective and invisible. 90 lumens is hardly bright enough to be seen with in just about any urban situation. Yet there are thousands and thousands of people riding at night with the thought that 'I can see. What do I need more for?', never understanding that they can't be seen and they are putting their lives at risk.
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    I've made my points, and to respond quickly to yours above:
    1) bike lights are no longer hard to see against other sources, and distance has nothing to do with it. A 500 lumen focused beam bike light hitting you in the face at night will give you a lasting blind spot.
    2) your statement about a laser beam is so ridiculous (me working with all kinds of lasers professionally for 30 years) that it discredits all you say about light, despite the "scientist" tag you use.
    3) helmet mounting of hard accessories like lights is a topic for A&S. It completely negates any slight benefit there is to wearing a helmet in the first place.

    We'll obviously never agree on this topic. Take it to A&S and I might respond further.

    In this time when LEDs are getting waaaaay more powerful very fast, bike lights won't be anything like you're used to using. All lighting is going to change in the next decade. The p-7 LED is just the start of it. The statement that "More is always better " is not true anymore. THAT's the only point I wanted to make.

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by RapidRobert View Post
    I've made my points, and to respond quickly to yours above:
    1) bike lights are no longer hard to see against other sources, and distance has nothing to do with it. A 500 lumen focused beam bike light hitting you in the face at night will give you a lasting blind spot.
    2) your statement about a laser beam is so ridiculous (me working with all kinds of lasers professionally for 30 years) that it discredits all you say about light, despite the "scientist" tag you use.
    3) helmet mounting of hard accessories like lights is a topic for A&S. It completely negates any slight benefit there is to wearing a helmet in the first place.

    We'll obviously never agree on this topic. Take it to A&S and I might respond further.

    In this time when LEDs are getting waaaaay more powerful very fast, bike lights won't be anything like you're used to using. All lighting is going to change in the next decade. The p-7 LED is just the start of it. The statement that "More is always better " is not true anymore. THAT's the only point I wanted to make.

    A 90 lumen light, no matter what the source, is difficult to see against a background of literally hundreds of other light sources that are of equivalent or, most likely, more powerful lights. It doesn't matter whether that light comes from an LED or from a halogen. 90 lumens isn't that easy to see nor is it a good source of light to see by. I know lots of people who ride with a similar light to wastan uses and they all complain about hitting potholes because they can't see them. Too many other light sources around for the low luminosity light of that kind of emitter to be effective.

    A 500 lumen light is in the upper echelon of light output even today. HID puts out around 500 lumens. Most commercial bicycle lights of any other kind available don't put out that much light. And, again, it is distance that matter more than output. 500 lumens from directly at the source is much, much brighter than even a few feet away and the intensity drops very quickly as the beam spreads out. At more than a few feet we ought to be talking lux rather than lumens because lux takes into account the area that the light is falling on.

    As for laser beam spread, most scientific applications try to keep the distance that the beam travels to a minimum. Why? Because scatter, beam spread and power all effect the beam as it travels through the air. For a laser, the beam at 60 feet is going to be significantly wider than it is at say 5 or 6 feet. Unless you use some kind of optics to recoluminate the beam, beam coherence is lost. If a laser beam were the same size from emitter to a target 50 or 60 feet away, we probably couldn't see it. Granted I haven't worked with many lasers (not really my field) but I've certainly played with a few and I have pretty good powers of observation.

    Helmet impact is generally to the sides of the helmet. I've had several impacts and not one has been directly on top of the helmet. Impact directly on top of the head is rare and, if it did occur, you'd have worse problems to worry about then a lamp on top of your head. Most mounts aren't permanent nor do they have parts protruding into the helmet. On impact to the light fixture with the ground, if the light even came in contact with the ground, the fixture is very likely to break off. Even if it didn't, the EPS is going to collapse just like it was designed to do and keep your brain from smashing into the side of your skull.

    Yes, lighting is changing but light isn't. The amount of light that can be had from smaller packages is wonderful. However, a lumen is still a lumen. The P7 pumps out lots of light because people want more light. The less energy they have to carry around to get that light, the more light they can carry and the more they are going to demand. I've been done a very long road to where we are today. I've done flashlights on the handlebars, turbocharged Cateye HL500, nominally volted halogen, overvolted halogen, MR11 and MR16 halogen, and LED. I've gone from 50 lumens to 4500 lumens. Each step up in light intensity has made me feel safer and more confident on the road. The one factor that is constant in this is that I like, and see the necessity for, more light output from the lamps I carry. The P7 lights I'm using right now are only for early fall when I don't need that much light because of the hours I ride. As it gets darker, I switch back to the higher output system because that is the safest for the kind of riding I do. But the one thing I would not do is go back to a 90 lumen light as my only source of light. More light is better. Every car manufacturer, lighting manufacturer, bicycle light manufacturer, etc. is trying to squeeze more light for less energy that they can. None of them want to go backwards. And few cyclists, once they have tasted brighter lights is going to be satisfied with less.

    Finally, ad hominiem attacks are no way to win an argument. Even if I have made a misstatement on lasers (which I have not), that does not negate everything I have said about what I have learned about lighting over the years as well as years of observation. It is pretty obvious if you would bother to do some research that at least some of what I say about lights and lighting is valid. If you have no valid reply to my points on positioning of bicycles, bicycle lights and their effect on other road users, then say so. Don't attack my knowledge as being completely lacking in merit because of one small possible misstatement. That's a logical fallacy which doesn't reflect well on you.
    Last edited by cyccommute; 10-04-09 at 09:22 PM.
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    "It is best to keep your mouth shut and be presumed ignorant than to open it and remove all doubt."

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    Quote Originally Posted by RapidRobert View Post
    "It is best to keep your mouth shut and be presumed ignorant than to open it and remove all doubt."
    Yes, yes. You really SHOULD have kept your mouth shut, Robert.
    "There is no greater wonder than the way the face and character of a woman fit so perfectly in a man's mind, and stay there, and he could never tell you why. It just seems it was the thing he most wanted." Robert Louis Stevenson

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    Quote Originally Posted by RapidRobert View Post
    More isn't better from the oncomming drivers' and cyclists' perspective. Too bright of a light from a tiny little source like an LED is dangerously distracting, and can very possibly cause temporary blindness in the center of the field of view. That's why it's against the law to not dim your headlights for oncomming traffic. THAT's a good law!

    Too much light can be a weapon. Shining too much light into the face of a nighttime driver is dangerous for EVERYONE on the road then, and for quite a while after the encounter. Do YOU want a temporarily blinded driver comming up behind YOU?
    Please stop parroting the same disinformation in every thread that someone asks about LED lights. Not only is it wrong, it's also a great disservice to people looking for info.

    BTW, have you actually ever used a high powered LED light? I use two, and they are pointed at the ROAD, not windscreens of oncoming cars.

    EDIT: I just saw in another thread that you have the high powered MAgicShine LED, yet here (and in other threads) you are warning against high powered LED lights. WTF, are you here just to argue?

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by RapidRobert View Post
    "It is best to keep your mouth shut and be presumed ignorant than to open it and remove all doubt."


    Non sequiturs now? That is all you have?
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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Ziemas View Post
    EDIT: I just saw in another thread that you have the high powered MAgicShine LED, yet here (and in other threads) you are warning against high powered LED lights. WTF, are you here just to argue?


    Most powerful LED available. But we mortals shouldn't use it. We should use the weakest lights around so that we don't offend other road users.



    I was going to be done with this guy but he's a hoot!
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    Hey Ziemas, learn how to read! I recommend against putting high poweered headlights on HELMETS, not against using them. I recommend against TOO MUCH light, and I'll add blinking headlights (which only paranoid cyclists use, and for no good reason).

    TOO MUCH headlight is inconsiderate to everyone comming toward you, other bicyclists included, and dangerous to everyone they encounter while temporarily blinded. Not ALL cyclists using high powered headlights adjust them propeerly. Just like not all helmet wearers adjust THEM properly.

    I don't care whether you like my recommendation or not. My words are for those who CAN comprehend my points and aren't blinded by their own paranoia about getting hit from the front. Nor do I care about the opinion of a pseudo-"scientist" who demonstrates his ignorance about light in general as he pontificates about it. Perhaps he should read a bit longer on the Wikipedia before posting such wordy drivel.

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    Senior Member Ziemas's Avatar
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    Quote Originally Posted by RapidRobert View Post
    Hey Ziemas, learn how to read! I recommend against putting high poweered headlights on HELMETS, not against using them. I recommend against TOO MUCH light, and I'll add blinking headlights (which only paranoid cyclists use, and for no good reason).

    TOO MUCH headlight is inconsiderate to everyone comming toward you, other bicyclists included, and dangerous to everyone they encounter while temporarily blinded. Not ALL cyclists using high powered headlights adjust them propeerly. Just like not all helmet wearers adjust THEM properly.

    I don't care whether you like my recommendation or not. My words are for those who CAN comprehend my points and aren't blinded by their own paranoia about getting hit from the front. Nor do I care about the opinion of a pseudo-"scientist" who demonstrates his ignorance about light in general as he pontificates about it. Perhaps he should read a bit longer on the Wikipedia before posting such wordy drivel.
    Do you even remember what you have written? I'll continue to use my helmet mounted LED, just as I have for several years. Some how I have yet to blind any drivers......Just how could that be?

    Quote Originally Posted by RapidRobert View Post
    More isn't better from the oncomming drivers' and cyclists' perspective. Too bright of a light from a tiny little source like an LED is dangerously distracting, and can very possibly cause temporary blindness in the center of the field of view. That's why it's against the law to not dim your headlights for oncomming traffic. THAT's a good law!

    Too much light can be a weapon. Shining too much light into the face of a nighttime driver is dangerous for EVERYONE on the road then, and for quite a while after the encounter. Do YOU want a temporarily blinded driver comming up behind YOU?

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    Hey Ziemas, how do YOU know the effects your lights have on the very few cars that might drive past you in Latvia? I'm an EXPERT on light. What do YOU do for a living? My recommendation was for those riding on roads with other traffic on them, which is very clear, and not those riding out where there's no oncomming drivers to blind!

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    Senior Member Ziemas's Avatar
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    Quote Originally Posted by RapidRobert View Post
    Hey Ziemas, how do YOU know the effects your lights have on the very few cars that might drive past you in Latvia? I'm an EXPERT on light. What do YOU do for a living? My recommendation was for those riding on roads with other traffic on them, which is very clear, and not those riding out where there's no oncomming drivers to blind!
    Wow an expert on light! Woo hoo! Because I've had exactly ONE car shine their brights at me, none honk, and more than a few give me a thumbs up at stop lights. Drivers are rather vocal about being blinded......BTW Bobby, I live in a city.......

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    Formerly Known as Newbie Juha's Avatar
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    Quote Originally Posted by RapidRobert View Post
    Hey Ziemas, how do YOU know the effects your lights have on the very few cars that might drive past you in Latvia?
    Riga is not exactly car free, you know?

    Seriously though, please let's keep the personal attacks out of this thread. This is not directed solely at you, Robert. Thank you everyone.

    --Juha, a Forum Mod
    Last edited by Juha; 10-05-09 at 09:31 AM.
    To err is human. To moo is bovine.

    Who is this General Failure anyway, and why is he reading my drive?


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  23. #23
    Formerly Known as Newbie Juha's Avatar
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    With that out of the way, here's my contribution to the topic. I'd love to see light manufacturers putting more effort into designing optics and lenses. With a conical flashlight beam such as Fenix L2D that I use, almost half the wattage and lumens go up in the air where it doesn't help me see at all, and it's highly unlikely it helps anyone else to see me better either. Wasted light.

    --J
    To err is human. To moo is bovine.

    Who is this General Failure anyway, and why is he reading my drive?


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    your nightmare gal chipcom's Avatar
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    Quote Originally Posted by RapidRobert View Post
    Hey Ziemas, learn how to read! I recommend against putting high poweered headlights on HELMETS, not against using them. I recommend against TOO MUCH light, and I'll add blinking headlights (which only paranoid cyclists use, and for no good reason).

    TOO MUCH headlight is inconsiderate to everyone comming toward you, other bicyclists included, and dangerous to everyone they encounter while temporarily blinded. Not ALL cyclists using high powered headlights adjust them propeerly. Just like not all helmet wearers adjust THEM properly.

    I don't care whether you like my recommendation or not. My words are for those who CAN comprehend my points and aren't blinded by their own paranoia about getting hit from the front. Nor do I care about the opinion of a pseudo-"scientist" who demonstrates his ignorance about light in general as he pontificates about it. Perhaps he should read a bit longer on the Wikipedia before posting such wordy drivel.
    Sorry, but from what I have read, Stu is pretty dead on and your credibility concerning both lighting and actual experience riding on or in the midst of bicycles isn't doing to well. I've seen lots of bright helmet mounted lights both driving and riding...they ain't no big thang.

  25. #25
    your nightmare gal chipcom's Avatar
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    Quote Originally Posted by Juha View Post
    With that out of the way, here's my contribution to the topic. I'd love to see light manufacturers putting more effort into designing optics and lenses. With a conical flashlight beam such as Fenix L2D that I use, almost half the wattage and lumens go up in the air where it doesn't help me see at all, and it's highly unlikely it helps anyone else to see me better either. Wasted light.

    --J
    That's because those torches were not designed as headlamps, they were designed as flashlights.
    Many of the bicycle specific lights focus the beam better because that is their intended application.

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