Hello,

Yesterday I fitted a H7 LED for the low beam to my xt660z. The bulb has a LED on one side. I can fit the bulb either facing the LED upwards or downwards.

Does anyone know if it matters how a fit the bulb?



When I look at the picture above the bulb is fitted with the LED down but in the manual that comes with the light it's facing upwards.

You do realise you won't be able to see jack sh!t at night with that bulb... either fitted facing up or down!

The locating lug on the bulb's base plate determines which way it fits. It will only go in to the back of the headlight unit one way.

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May I ask why you don't see anything at night with this bulb?

You have to fit the grey base plate with the lug first. In this baseplate you can fit the rest of the light just like for example a normal rear light bulb is fitted. You can fit it with the LED facing up or down.

Mainly because the headlight reflector (and lens to a degree) are designed to work with a filament type bulb and not an LED, or HID for that matter. The nature of LED bulb design means that they are a bulky affair and there has to be a considerable supporting structure for the diodes which is opaque and interrupts the dispersal of light. Also, in the example shown in your photo, the three diodes are spread over a relatively wide area; the light emitting zone is not in one place so the light source is impossible to position at the focal point of the reflector (or the point at which the reflector was designed for). A traditional halogen bulb glows most brightly at the exact centre of the filament in a tiny but dense area which can sit at the focal point and crucially, the light emitted from that spot travels in every direction (360 degrees in every plane) and can make full use of the whole reflecting surface, unlike an LED bulb which can only emit light in one direction and at best to about 160 degrees.

A lot of baloney is talked about Lumens, but it is not a very good measure of the effectiveness of a light source. Lumens is an over simplistic measure of total light produced, not the amount that is focussed and 'useful'; it looks good on paper, which is why it's often quoted in the sales pitch. Lux is a far better measure at it is 1 Lumen per square metre, in other words focussed, useful light. An LED bulb may produce 3000 Lumens on the test bench and a halogen bulb just 1600, but with the halogen bulb nearly all the 1600 Lumens are useful. Generally speaking an LED bulb in a non-standard installation will be a third of the efficiency (two thirds of the Lumens are wasted). Your LED bulb will 'look' brighter (mainly because of the higher colour temperature tricking your eyes), but who looks at their headlight? It will more than likely put two thirds less 'focussed' light on the road, plus high colour temperature (bluer) light is far more prone to scatter than light towards the red end of the spectrum so in fog, rain etc. it will be even less efficient.

Aftermarket HIDs are slightly better, but the arc which emits the light is most intense at each end (think of it as 'dog bone' shaped). The weakest part of the arc is at the focal point meaning less focussed light and loads of glare, scatter and wasted light caused by the bright ends of the arc sitting outside the focal point. This is mainly why aftermarket HIDs 'appear' brighter (colour temperature helps this illusion) and why they are an annoyance to other road users.

HIDs work most efficiently in purpose designed refractor, or projector headlight units. LEDs only work anything like properly in purpose designed complete units such as you see on top end Audis, BMWs etc. and you should take a look at the complexity/expense of the design including the intelligent cooling system and massive heat-sinks required to reduce junction temperature.

Fit them, see how you get on with them... but don't expect miracles!

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Thanks for your explanation

I have a load of spare hid bits here from various previous bike/car projects. I have 4300 and 6000k h7 bulbs and a suitable ballast box,but earlier this year I quickly looked at fitting a kit to my xt660z and recalled a strange mounting ring holding in the original standard bulb so left it as is.
What way do others modify this mount to accept an alternative bulb.

Cheers

Colin J

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2011 xt660z.
Yoshimura cans ,kev mod,Dna 2, Stahlkoffer panniers,Hepco Becker box,Givi crash bars,Mita e07 tyres.

Beam adjustment will make little or no difference to the annoyance factor, the point being that the annoyance is caused by glare and scatter from the unfocused portion of light - that which lies outside the 'beam'.

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According to scientific theory (and practice) the above 'Pepsonian' theory doesn't quite hold water. The flaw being that light scatters, and it is most evident not in a solid or liquid, but gases - which, as far as I am aware, the atmosphere through which our headlights shine is composed of! The scientist Lord Rayleigh discovered this in the late 19th century - a very very long time before HIDs were thought of.

Scatter is what causes glare, and glare is what causes aftermarket HIDs (and LEDs) to be an annoyance.

Do a quick search on Rayleigh Scattering and you see where the issue lies. Here's a snippet from Wikipedia to whet the appetite...

Rayleigh scattering (pronounced /ˈreɪli/ ray-lee), named after the British physicist Lord Rayleigh (John William Strutt),[1] is the (dominantly) elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. Rayleigh scattering does not change the state of material and is, hence, a parametric process. The particles may be individual atoms or molecules. It can occur when light travels through transparent solids and liquids, but is most prominently seen in gases. Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle therefore becomes a small radiating dipole whose radiation we see as scattered light.

Whilst I get where you're coming from and I don't disagree that YOU can see better at night with your HID headlight, we'll have to agree to disagree on the annoyance issue. I'm sure the roads are quiet at night down in Portugal, hardly any oncoming traffic, but here in the UK, aftermarket HIDs have become a real menace in the last five years, despite it meaning an MOT fail (for cars anyway).

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And glare is something that your eyes detect without actually looking at the light source. No one looks directly at the sun (unless they're daft), but we all wear sunglasses in the summer because of... glare.

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I better not go out at night then!

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