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Date:         Mon, 15 Nov 1999 14:34:54 -0800
Reply-To:     al_knoll@HP.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Al Knoll <al_knoll@HP.COM>
Subject:      Sharp Cutoff Headlights
In-Reply-To:  <199911151933.LAA29851@palrel3.hp.com>

Item Subject: cc:Mail Text

For most DIN headlights and most "EURO" headlights that have replaceable elements, the Hi-Lo beam has a designe feature that provides a very distinct "cut-off" of the beam. The visible light above the cutoff on low when looking at the light rather than looking with the light is very low intensity. Below the cutoff the light is much brighter. The feature provides the very best rain/fog/snow performance and has the additional advantage of not "dazzling" the oncoming driver as the cutoff section covers the opposing traffic lane in relative shadow.

On high or high+low the beam is of course not baffled and will as you would expect 'dazzle' the oncoming traffic.

For a vanagon this presents an interesting problem. If you aim your lows to illuminate the road fairly far away but still with a down cutoff, the high beams are suitable for jacklighting owls. If you aim your high beams so they point parallel to the road surface the lows are quite suitable for jacklighting tarantulas. Has to do with the relatively high placement of the lamp center with respect to the road.

Carello, Cibie, Marchal, Lucas and others produced some special 7" round lights that have their focus adjustable for low or high placement on the vehicle. The most famous were the dual bulb Carellos and the Marchal Ampilux. Fitted with 100 and 130 H1 bulbs these were the answer at Daytona, Sebring, Le Mans and the Bol d' Or for race cars that had very low light centers. No dazzle and difficult to overdrive even at race speeds. Alas, no more.

The cutoff design permits adjustment for no dazzle regardless of the lamp intensity on low beam so "blinding" other drivers is merely a case of poorly adjusted headlights and has no bearing or relevance to the H4 or H1-H1 designs.

The H4 is a fixed focus unit and doesn't permit independent filament placement so we have an inherent design compromise which still doesn't dazzle the oncoming driver.

Cibie made a Z-beam which instead of the tipped up RH beam pattern had a horizontal sharp cutoff LH side with an elevated but also horizontal sharp cutoff RH side (on a per headlight basis of course, R and L are indentical.

For LH driving countries such as NZ and Merrie Old there is an opposite lamp which has the cutoff on the right.

Wish I'd never sold the Ampilux with the TI Super.

al


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