R7s linear halogen lamps: what sits inside floodlights

How the R7s linear halogen lamp used in floodlights and uplighter floor lamps is built, its lengths, how to handle it, and the LED alternatives.

Open an old floodlight in the yard and, instead of the bulb you expect, you find a thin glass rod with a metal-capped contact at each end. The same lamp appears in older floor-standing uplighters that throw light at the ceiling. This is the R7s linear halogen lamp. For years it was a popular source of cheap, powerful light, but its intense heat and short life have made it one of the lamps most often replaced today.

How it is built

An R7s lamp is a slim tube of quartz glass. Inside, a coiled tungsten filament runs along the length of the tube, held away from the walls by small wire supports. The tube is filled with halogen gas, which returns tungsten evaporated from the filament back onto it and prevents the glass from blackening.

The base name describes the contacts at both ends. Each end of the lamp has a ceramic or metal cap with a small contact tip, and the lamp is held by being clamped between two spring contacts in the fitting. The "7" in R7s refers to the contact tip diameter of about 7 mm.

Lengths: the key dimension

R7s lamps are made in a few standard lengths, and a fitting is built for one of them:

• 78 mm: small floodlights and compact fittings;
• 118 mm: the most common size, for medium and large floodlights and uplighters;
• 189 mm and 254 mm: very high-output industrial and site floodlights.

Length is measured between the contact tips. The wrong length either does not go in or is not gripped properly by the spring contacts, leading to heat and arcing. Measuring the old lamp before buying is essential.

Handling rules

A halogen R7s works at a very high temperature, so it has its own handling rules:

• Do not touch the quartz with bare hands. Oil from skin creates a hot spot on the glass when it heats up, and the lamp can crack or even burst. Use a cloth, paper or a clean glove when fitting it. Accidental fingerprints should be cleaned off with alcohol once the lamp is cold.
• Let it cool. After switching off, the lamp and the floodlight housing stay very hot for a long time.
• Keep the protective glass in place. A floodlight's front glass protects not only against rain but also against fragments if the lamp bursts.
• Horizontal position. Many R7s lamps are designed to run horizontally only; tilted mounting shortens their life.
• Away from flammable materials. There should be no curtains, fabric or paper near uplighters and floodlights.

LED R7s: a simple-looking but limited swap

LED lamps with an R7s base are available. They let you keep the old fitting, but there are a few limitations to know about.

First, size. LEDs need room for diodes, driver and heat sink, so an LED R7s lamp is considerably thicker than the halogen one and may not fit a narrow floodlight or uplighter reflector.

Second, light distribution. A halogen filament spreads light evenly around the tube, and the floodlight's reflector is shaped to gather it. In LED R7s lamps the diodes often face one or two sides only. The lamp has to be oriented correctly, or part of the light is lost in the reflector.

Third, output. Matching the light of a high-wattage halogen R7s with an LED of the same size is difficult, because getting the heat out of a powerful LED in such a small body is a problem.

In dimmable uplighters, the LED R7s lamp's dimmer compatibility also needs checking separately.

Replacing the whole fitting

For old outdoor halogen floodlights, the most sensible solution is often to replace the floodlight rather than the lamp. Integrated LED floodlights:

• produce much less heat and reduce the risk of burns;
• need no lamp changes;
• come in a ready-made housing with a stated protection rating;
• allow the beam angle to be chosen for the specific task.

With uplighters, however, if the decorative body is worth keeping, a suitably sized LED R7s lamp is worth trying.

Quick check

• Measure the old lamp between its contact tips.
• Is there enough room inside the fitting for the diameter of an LED lamp?
• Is the fitting dimmable?
• Are the floodlight's protective glass and seal intact?

The Zəfər İşığı catalogue also includes a halogen lamp with an E40 base. Whatever technology you choose, the safety rules around heat and glass are just as important when working with halogen lamps.