Real life visual, Halogen bulbs in mini lightbars replaced with LED.

May 21, 2010
1,256
Minnesota
I have read plenty of questions and debate over the years about using an LED replacement for a halogen bulb in a rotating lightbar. Tonight I saw one of the best examples of why this is not a good idea for bulbs like the H1 or 795 when using as a warning light. When I first saw the truck I thought they were just flashing lightheads. Because blinkies draw me like a moth to a flame I looked closer and realized they were rotators. At least the driver does not need to worry about light bounce back, lol. (a little more info/observation in the video description if interested)

 
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Fyrtwuck

New Member
Oct 19, 2020
4
Oklahoma
Interesting. I’m in the process of restoring a Federal Streethawk and I replaced my bulbs with LED bulbs. INSIDE my house, they appear to be much brighter than the halogen.

Now, I’m going to have to do a comparison. I think I’ll put the halogens back in on one side of the bar and see which is better. Whichever is brighter and throws more beam gets to stay.
 

shues

Lifetime VIP Donor
May 21, 2010
10,276
NW Indiana
What's telling is the extreme angle at which the bulk of the light leaves the reflector. Look at the pattern shone on the toolbox by the one driver's side rotator with a working bulb. This video is proof positive that LED replacements cannot put light into the focal point of a parabolic reflector designed for incandescent or halogen lamps.
 
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GE

Member
Sep 30, 2015
109
Prairies Canada
That they're LED is of little importance. What is of major importance is the way LED replacement bulbs are constructed versus halogen.

Halogen and incandescent bulbs use a tungsten filament as a resistive element which glows very brightly to produce light. Compared with an LED it is extremely small for the luminosity provided, and is capable of producing light in essentially 360 degrees. There are also different ways the filament is oriented in the bulb which places the light in different positions relative to the center of the bulb. Halogen reflectors are engineered very specifically to focus light coming from the bulb in a controlled and predictable manner. If you take a horizontal-filament bulb and place it into a housing intended for a vertical-filament bulb, you will lose effectiveness.

LEDs are directional. The way these replacement bulbs compensate is to use multiples of them arranged radially to produce 360 degrees of light. Absolutely none of them place the same quantity of light in the same location as a tungsten filament, which is why nearly 100% of LED replacement bulbs are non-compliant and illegal for use on most public roads (enforcement however is virtually nil).

If an LED bulb was constructed so as to exactly match the position and luminosity of the tungsten filament it replaces in the halogen bulb, you would see a viable alternative to place into rotators like the ones above. The current technology is probably close but I haven't seen anything suitable for use in a rotator. Given that LED beacons and mini-bars are widely available, cheap, and generally bright and effective, there's little reason not to just replace the entire lamp.
 

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