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Headlights: candlepower vs. watts

post #1 of 10
8/11/04 at 3:28pm
Thread Starter 
Candlepower is a measure of light emitted; watts is a measure of
power output. How come inexpensive clip-on headlights are rated by
candlepower but expensive lights with separate battery units are rated
by wattage? Can you convert from one to another?

Here's specifically what I'm getting at: I use a Sigma Sport Mirage X
with 5 and 20 watt lights for winter commuting on dark country roads,
but it's too heavy and bulky to keep on the bike all the time. I want
to keep a smaller, cheaper light in my commuting bag to throw on the
bike if I work late in fall or spring when I don't have the Mirage
lights, and to put on other bikes I may take to work occasionally.
Obviously it won't have nearly the power of the Mirage lights, but
should be enough to be seen and kind of see the road. I'm trying to
get a sense for how bright one of these things will be compared to the
my 5 and 20 watt lights.

So, what's the brightest self-contained light? The Cateye EL-500
claims 1000 candlepower; how does that compare to a wattage rating?

Thanks,
Michael
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post #2 of 10
8/11/04 at 5:13pm

Re: Headlights: candlepower vs. watts

Quote:
Originally Posted by Michael Press
Candlepower is a measure of light emitted; watts is a measure of
power output. How come inexpensive clip-on headlights are rated by
candlepower but expensive lights with separate battery units are rated
by wattage? Can you convert from one to another?

Here's specifically what I'm getting at: I use a Sigma Sport Mirage X
with 5 and 20 watt lights for winter commuting on dark country roads,
but it's too heavy and bulky to keep on the bike all the time. I want
to keep a smaller, cheaper light in my commuting bag to throw on the
bike if I work late in fall or spring when I don't have the Mirage
lights, and to put on other bikes I may take to work occasionally.
Obviously it won't have nearly the power of the Mirage lights, but
should be enough to be seen and kind of see the road. I'm trying to
get a sense for how bright one of these things will be compared to the
my 5 and 20 watt lights.

So, what's the brightest self-contained light? The Cateye EL-500
claims 1000 candlepower; how does that compare to a wattage rating?

Thanks,
Michael
You are asking for the answer to a very complex question in comparing candlepower to wattage rating.
First, to correct one of your assmptions, wattage is the input power supplied.
The useful output power can be measured in candlepower or lumens.
Even when comparing two or more lights with the same rated candlepower/lumens it is very difficult because of things like how the light is distributed in "beam pattern" and how it is distributed in the spectrum... light frequency (or frequencies). Since our eyes have different sensitivities to different frequencies... and very little to infra-red and/or ultra-violet, you would prefer that the input power is utilized in creating a beam pattern and light frequency suitable to you and your riding.
Now, to a more practical answer... I hope. Take a look at the ViewPoint Gen 3 LED Headlight offered by Performance Bicycle. URL:

<http://www.performancebike.com/shop/profile.cfm?SKU=18633&subcategory_ID=4320>

It uses 4 AA batteries. You can use the rechargeable NiMH batteries in it and have a "fall-back" of Alkaline cells. It is pretty bight and relatively compact.
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post #3 of 10
8/11/04 at 6:42pm

Re: Headlights: candlepower vs. watts

Watt is a measure of power, not light output. HID systems consume far less power than incandescent of similar output.
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post #4 of 10
8/11/04 at 8:42pm

Re: Headlights: candlepower vs. watts

> Candlepower is a measure of light emitted; watts is a measure
> of power output.

Candlepower is a measure of light intensity, watts is a measure of power
input.

> How come inexpensive clip-on headlights are rated by candlepower
> but expensive lights with separate battery units are rated
> by wattage?

In a word: marketing. A low-power headlight that is well focussed can
still produce a high candlepower reading at the illuminated spot, and
that is what sells the headlight.

> Can you convert from one to another?

In a word: no. A spread-out beam from a 20-watt halogen headlight may
have a lower candlepower rating than a tightly-focussed beam from a
1-watt LED, even though the 20-watt halogen may be effectively
illuminating the entire width of the road, whereas the spot from the
1-watt LED is only a few feet in diameter.

> I want to keep a smaller, cheaper light in my commuting bag to
> throw on the bike if I work late in fall or spring when I don't
> have the Mirage lights, and to put on other bikes I may take
> to work occasionally.

I like the Sigma Sport Ellipsoid for that purpose, but I use two of
them, as one just does not provide enough light. A big advantage the SSE
has over most other headlights is that the batteries don't have to be
removed for charging, as the charger simply needs to be plugged into the
housing, which has a jack for the purpose.

> So, what's the brightest self-contained light?

A really adequate single-unit headlight is the Holy Grail of bicycle
lighting, and I don't think anyone has found it yet. I know I haven't.
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post #5 of 10
8/12/04 at 9:29am

Re: Headlights: candlepower vs. watts

LioNiNoiL_a t_Y a h o o_d 0 t_c 0 m wrote in message ...
>
>A really adequate single-unit headlight is the Holy Grail of bicycle
>lighting, and I don't think anyone has found it yet. I know I haven't.
>
Ever Ready Nightrider provides general forward illumination with a 3" dia.
lens plus side spots and rectangular beam to light the road. Achieved with
two D cells and 3W halogen filled incandescent bulb.

Trevor
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post #6 of 10
8/12/04 at 8:55pm

Re: Headlights: candlepower vs. watts

>> A really adequate single-unit headlight is the Holy Grail of
>> bicycle lighting, and I don't think anyone has found it yet.
>> I know I haven't.
>
> Ever Ready Nightrider provides general forward illumination
> with a 3" dia. lens plus side spots and rectangular beam to
> light the road. Achieved with two D cells and 3W halogen
> filled incandescent bulb.

A single 3W halogen certainly provides general forward illumination, but
a great many bikers, myself included, do not consider it adequate.
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post #7 of 10
8/13/04 at 3:35pm

Re: Headlights: candlepower vs. watts

LioNiNoiL_a t_Y a h o o_d 0 t_c 0 m wrote in message ...
>>> A really adequate single-unit headlight is the Holy Grail of
>>> bicycle lighting, and I don't think anyone has found it yet.
>>> I know I haven't.
>>
>> Ever Ready Nightrider provides general forward illumination
>> with a 3" dia. lens plus side spots and rectangular beam to
>> light the road. Achieved with two D cells and 3W halogen
>> filled incandescent bulb.
>
>A single 3W halogen certainly provides general forward illumination, but
>a great many bikers, myself included, do not consider it adequate.
>
Notice this unit also has a beam which if mounted on handlebars provides an
illuminated patch on the road sufficient to ride at 18mph.

Trevor
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post #8 of 10
8/13/04 at 5:29pm

Re: Headlights: candlepower vs. watts

>>>> A really adequate single-unit headlight is the Holy Grail of
>>>> bicycle lighting, and I don't think anyone has found it yet.
>>>> I know I haven't.
>>>
>>> Ever Ready Nightrider provides general forward illumination
>>> with a 3" dia. lens plus side spots and rectangular beam to
>>> light the road. Achieved with two D cells and 3W halogen
>>> filled incandescent bulb.
>>
>> A single 3W halogen certainly provides general forward
>> illumination, but a great many bikers, myself included,
>> do not consider it adequate.
>
> Notice this unit also has a beam which if mounted on handlebars
> provides an illuminated patch on the road sufficient to ride
> at 18mph.

I can show you roads on which moonlight alone is sufficient to allow
18mph; that doesn't mean moonlight is "sufficient".
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post #9 of 10
8/14/04 at 5:00pm

Re: Headlights: candlepower vs. watts

LioNiNoiL_a t_Y a h o o_d 0 t_c 0 m wrote in message ...
>I can show you roads on which moonlight alone is sufficient to allow
>18mph; that doesn't mean moonlight is "sufficient".
>

I have driven at 40mph on unknown roads illuminated solely by the moon, the
eye will adapt. If I can see ahead that the road surface is even and
unlittered there is sufficient light for me to see to ride or drive. If
every road user used marker lights and everyone complied with not to ride or
drive faster than the speed at which you can stop in the distance you can
see to be clear, all roads would be safe.

How fast do you want to ride of a night on unlit roads? Is it lit roads you
have the problem with? Either way a detailed eye examination, I think is
called for.

Trevor
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post #10 of 10
8/14/04 at 6:38pm

Re: Headlights: candlepower vs. watts

>>>> A single 3W halogen certainly provides general forward
>>>> illumination, but a great many bikers, myself included,
>>>> do not consider it adequate.
>>>
>>> Notice this unit also has a beam which if mounted on handlebars
>>> provides an illuminated patch on the road sufficient to ride
>>> at 18mph.
>>
>> I can show you roads on which moonlight alone is sufficient
>> to allow 18mph; that doesn't mean moonlight is "sufficient".
>
> If every road user used marker lights and everyone complied with
> not to ride or drive faster than the speed at which you can stop
> in the distance you can see to be clear, all roads would be safe.

If wishes were horses, then beggars would ride.
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