A legal bulb can still dazzle

From 14 October, MOT testers in Britain have to accept some approved LED bulbs where they belong in a compatible halogen lamp. The permission is narrow. It is not a licence for any bright bulb in a listing. The desk has not fitted one, and we will not score a brand from a rule.

The beam is the part that matters

A lamp is kind when the light falls on the road and the verge, and unkind when it sits in the eyes of the driver coming the other way. Approval says the bulb was made to a pattern. It does not say the pattern survived the fitting, or that a different bulb from the same shelf will do the same job. We have driven behind cars whose lamps looked white and whose light arrived in our mirrors. The colour was not the problem. The height of the beam was.

The number plate lamp is the small one, and it has the same duty. It has to show the plate, not a patch of glare beside it. A plate you cannot read from a short distance is a failed lamp, however new the bulb looks.

The boot can wait

People change a bulb because the old one has died, often in a car park, with a phone for a torch. That is a fair reason. It is a poor reason to take the brightest thing the page will sell. The cloth and the old bulb can stay in the boot until the car is somewhere you can see what the new light actually does. A phone light on the leaflet is not a check of the beam. The check is the road in front, and the face of the driver who meets you.

What we will keep

We will keep the rule in the size it was written. An approved bulb in the right lamp is allowed. A brighter bulb that paints the cabin of the car ahead is not a kindness. The list stays short: the beam on the road, the plate readable, and no shopping substitute for either one.