An R7s bulb is the slim glass tube with a metal contact at each end that sits inside security floodlights, uplighter floor lamps and picture lights. There is no thread and no pins to line up — the tube is sprung into place between two contacts, which is why the only measurement that matters when you replace one is its length.
Open the fitting and look for a small ceramic holder on each side, one of them on a visible spring. If the old tube is still in place, it will be marked along the glass with its wattage and often its length. If the glass has shattered and left the ends behind, switch off at the consumer unit before you go near it: the ends stay live and are held under tension.
Lengths are quoted end to end across the two contacts, and the common sizes are 78 mm, 118 mm, 189 mm and 254 mm. A tube 2 mm short will drop out; one 2 mm long will bow and crack. Measure the gap between the holders with the spring at rest, not compressed, and buy to that figure rather than to whatever the fitting was originally sold with — replacement holders get fitted over the years and the gap changes.
There are also two cap diameters, 7 mm and 15 mm. Domestic lamps are almost always the 7 mm version; the 15 mm cap belongs to high-wattage professional floodlights.
Most R7s tubes sold for decades were linear halogen: cheap, instantly bright, fully dimmable, and hot enough to scorch anything resting against the glass. Linear halogen with an R7s cap below 2 700 lumens can still be sold in the EU, but the higher-output versions have not been placeable on the market since September 2023, so a 400 W or 500 W floodlight is on borrowed time.
LED replacements draw a fraction of the power and run cool enough to handle. The trade-off is the beam: halogen throws light all the way round the tube, while an LED version carries a driver and a circuit board inside and typically emits over 120 to 330 degrees. In a floodlight or an uplighter that is irrelevant — you can rotate the tube so the emitting face points where the light is wanted. Behind clear glass on a decorative fitting, the dark side shows.
Be honest about lumens when you swap. A 118 mm 120 W halogen tube is typically somewhere above 2 000 lumens, and many LED tubes of the same length sit well below that. Read the lumen figure rather than the "equivalent wattage" claim on the front of the box.
Usually yes, as long as the length matches and the fitting is not sealed so tightly that heat has nowhere to go. Nothing else in the fitting needs changing.
Wrong length, almost always. A tube that rattles is short; one that has to be forced is long.
Halogen always is. LED only when the packaging says so.
Other cap types and shapes are listed under light bulbs.
