This is a simple question with (I hope) a simple answer. Please fill in the blanks:

The light output from a 1 watt luxeon LED headlight is equivalent to the light output of a _____ watt halogen or a ____ watt HID.

5, 2.5

I did some side-by-sides in the garage last fall. My Planet Bike SuperSpot has a hot spot in the middle which is about as bright as a 10W MR11 halogen. But the superspot only has that brightness in a little 2-foot-across spot; the halogen holds it for a nice wide beam. So I think total light output must be about half, possibly even less than that.

The HID number is a guess. My 13W HID is considerably brighter than my 20W halogen, so I just divided by two.

LEDs are efficient, that's for sure, but IMHO a 1-watt is only good for secondary or emergency lighting. I'd like to see the new 3 and 5 watt units in person, but I'm sure as heck not shelling out for them after my experience with 1 watt units.

A one watt Luxeon LED is about the equivalent of a HID with the battery disconnected.

A one watt LED is equivalent to a 1.25 watt halogen is equivalent to a 0.5 watt H.I.D.

Please check the base post on the light selection guide sticky. This is all explained. The comparsons with a one watt Luxeon LED is way off the reality. The Luxeon emits about 25 lumens, my halogen emits 1000 lumens, and a HID emits about 600 lumens. A Luxeon rates as a blinky on my bike. A rider with a 3 LED light showed up on a club ride last March. The three other riders had lights 50 to 100 times as powerful.

LEDs can be seen for a considerable distance, and look intense from a long way off. But they have a beam throw that sucks majorly. To get a beam throw from LED lights that comes anywhere close to an incandesant bulb, you'de have to stack a lot of LEDs in an array. By then, the power savings LEDs are known for goes up in smoke. You'de been better off just running the halogen.

Comparing LED headlights to halogens and HIDs is like comparing pinpricks to a broadsword wound.

This is not a simple question. For a detailed discussion of some of the issues, read this article: https://www.electro-optical.com/whitepapers/candela.htm

Also, look at the chart at the end of the article comparing typical levels of luminence, because it shows how bad the human eye is at comparing brightness. Would you believe that bright sunlight is 1000 times brighter than typical residential illumination?

In short, the usefulness of a light source is determined by three things: how much of the electrical energy consumed is converted to light, how that light is dispersed, and how well the human eye processes the color produced.

If two lights are producing the same amount of light, but one is a floodlight and the other is a spot, the spot will appear brighter. If two lights are producing the same amount of light and one is red and the other white, the white will appear brighter.

Comparing lights is not just hard for cyclists, it's hard for everyone, and there is not a good number to use for rating them. Sometimes lights are rated in lumens, which is total light produced, irrespective of color or beam angle. As an analogy, think of a sprinkler rated in gallons per minute. This measure is only really useful for comparisons if a light emits equally in all directions, and is not normally used for lights with reflectors. Lights with reflectors are usually rated in "center beam candlepower" which is adjusted for color and measures the brightness of the brightest part of the beam. The problem with that as a measure is that it says nothing about the rest of the beam. A halogen beam with a flood pattern has about one-sixth the center beam candlepower of one with the same wattage and a spot beam.

Manufacturers seem reluctant to publish candlepower figures, but here are some samples I got from googling:

A 1W luxeon will give you about 200-400 center beam candlepower.

The Topeak Moon Shine HID is rated at 10w, 1300 candlepower.

A Sylvania 35W MR-16 halogen bulb is rated at 11,000 candlepower for a narrow (8-degree) spot and 1400 candlepower for a flood (40-degrees).

(I love this quote from the article: "At the threshold of vision the dark adapted observer can see a flash if it contains on average 90 photons at the cornea or 9 at the retina. This is equivalent to a candle at 30 miles on a clear night.")

I should amend my posting by saying that the perceived brightness is really hard to gauge. I think in reality the LED is really pretty weak. When that's all that's on at night it seems fairly bright. However, when I'm running with an LED, I get blinded by car headlights very fast. With my halogen, only for a couple of seconds as they approach, and with HID, not at all.

Thanks. Question answered.

or, maybe a little less.

This has to be caused by the adabtability of the eye. When I photographed the LED based lights I have in my possession, I used the same camera settings for all of the lights. Your eye doesn't do this, it is constantly updating based on the information it receives, if the light dims, your pupil opens and vise versa. It would be worthless for comparison if I let the camera do this.

The biggest problem with the LEDs, is the lack of light spillage. There are some very good LED based lights out there, and they have the strengths and weaknesses like halogens (abysmal run times) and HIDs (very expensive). The can be made small and light, as well as bullet proof. That said, the 1 watt based lights do not put out the light that even a 10 watt halogen does, but would make a nice compliment light for helmet, if you have a bar light.