THINGS YOU NEED TO KNOW…
Spot, flood or flasher?
The biggest market for LEDS in the aftermarket is indicators, with the styling freedom that comes from their small size and increased visibility to other road users. Rear lights fall into the same category, with tail tidies. Then you’ve got auxiliary running lights, also known as Daytime Running Lights (DRL). LEDS are very directional compared to filaments, but you’ll often see a choice of 10 or 30 degree light spreads for DRLS. This is essentially the difference between a spot or flood-light pattern, which also determines how much more visible you are to other road users by using different optics for spread and light pattern. Indicators will have a line of LEDS for rear visibility with one on the end to cover the side-view.
DRLS and the Law
The DFT advice aimed at car drivers is that: “DRLS are necessarily bright to ensure they are visible in the daytime, but not so bright that they will dazzle others.” On bikes it makes sense to have them set so they aren’t going to dazzle other road users, too, with the optimum set-up wired through the headlight and coming on with the ignition, but with a switch to override the standard lighting circuit. That also makes passing an MOT easier as switchable items aren’t tested. However, a pedantic MOT tester could refuse to pass your bike if the lights aren’t E-marked, so look for that when you buy. And go for dual-intensity set-ups which can be set to low to match dim, and high for full beam.
Fight the power
Although the power draw from an LED is minimal they can have an effect on CAN Bus systems. You need to be careful about adding them in, and BMWS and KTMS in particular seem to be sensitive to DRLS for instance. When fitting, it may be necessary to buy trigger wire adapters or specialist wiring kits for fitment. That low power draw can also have an effect on indicator flasher speed, making them flash on and off like a Techno club’s lighting rig. In that case, any set-up has to have resistors built in to get the flash rate where it should be.
Normal (filament) bulbs
Normal (filament) bulbs draw a relatively high current for such a small device as the current is used to make the filament white hot and give off light as a by-product. Those light bulbs are basically a small heater and an extremely inefficient light source. Hence, the wattage value of a bulb is also used as an indirect (and inaccurate) measure of how much light it gives off. Sometimes a modern flasher unit uses a timer circuit to maintain the flash rate, irrespective of the load. Changing the type of bulbs does not always cause a problem; it depends on the design of the flasher unit. Otherwise, the resistor required for the flasher to continue to operate correctly depends on what bulb was originally fitted (i.e. what was the original load) and what is the load of the replacement (i.e. how much we are changing the load). If you replace two 21W bulbs with 2W LEDS, you’ve got to add a load of 38W to make sure the same current is pulled through the flasher relay.