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Old 01-11-2012, 11:27 PM   #67
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Joined: Dec 2005
Location: San Felipe, Baja
Oddometer: 1,926
Nice photos TT.

Here are some preliminary (see below) lumen reports.

BD Soltek 8" driving light: 2077 lumen
BD Squadron LED: 1639 lumen

Lights were measured using a 250 watt 13.8 volt regulated supply. All measurements were taken in a darken room. Foot-candle measurements were taken at 1 degree field angle increments on a horizontal plane at beam center. Measurements below 10% of peak lumen were not included. The 10% lumen cutoff was at a 10 degree field angle for the race light and 22 degree field angle for the LED.

Interestingly, if the lumen cutoff is set at 5% the LED lumen output remains the same while the race light lumen output increases to 2500. What this means is that the race-light has a more distribution to the sides without the sharp drop off in light. Or put another way, the LED has a more focused beam. You can see that in the pictures as a bright spot in the middle of the field.

Just for fun I also measured a low cost Custom Products 4" HID. This light measured 8056 lumen at a 40 degree field angle. It also exposed a flaw in my measurements. The measurements were all taken on a horizontal line based on the lamp or beam center. That works fine for a lamp with an even (ie round) field. What was obvious with the CP light was that this method does not work with a fixture where the light output is focused into a beam that is wide in the horizontal plane and narrow in the vertical plane.

The original design was to use a stand with the light mounted on a rotary table and aimed at a light meter. This allowed me to rotate the fixture a set amount and to take a measurement. The advantage of this is the distance from the fixture to the target (light meter) remains the same. That makes the calculation and measurements easier.

The CP light, you can see the wide horizontal spread with minimal vertical spread.

The new test fixture will use a target with measurements taken at different quadrants in the beam field. That should account for differences in the vertical spread of the beam. As a side note, the BD fixtures appear to have a fairly flat field so the lumen comparison between the Soltek and Squadron fixtures should be close. Here is the Squadron field, the target board is at 20' from the fixture.

More to come as time allows.
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