Candle or golf ball? How to measure a replacement light bulb

A replacement bulb can have the right screw cap and still catch on the shade or stick out past its rim. Take two measurements before you shop. Maximum body width tells you whether it can pass through the opening. Overall length, including the cap, helps you compare how far it could project once fitted.

Measure the old bulb and check the fitting

1. Identify the cap. Read the marking on the old bulb or fitting. Both examples below use an E27 screw cap. Check yours separately, especially on small decorative lights.
2. Measure a cool bulb that has already been removed. Use a ruler across the widest part of the glass. Then measure from the tip of the glass to the end of the cap.
3. Check where space is tight. Look at the narrowest point the bulb must pass through and the space where the glass will sit. A recessed holder, tapered shade or side opening can affect the fit. Compare with an old bulb that fitted well and leave room for the clearances required by the fitting maker.

Two E27 examples with different proportions

Both Integral examples are rated at 470 lumens and 2700 K warm white. Their shapes solve different space problems.

For a narrow opening. At 40 mm across, the opening is smaller than the 45 mm golf-ball body. The 35 mm candle passes that width comparison. You still need to check length and working clearance.

For a short bulb. If an 85 mm overall length is your comparison limit, the 82 mm golf ball passes that check and the 93 mm candle exceeds it. Check the width as well. An external shade depth alone won’t tell you your bulb-length limit because the position of the holder matters.

Before ordering

Confirm the cap, both measurements and the fitting’s instructions. If you use a dimmer or the shade is enclosed, check the bulb and fitting maker’s compatibility guidance. If a few millimetres will decide the fit, confirm the exact model on the supplied pack and check the real clearance.

Catalogue dimensions are from Integral’s ILCANDE27DC042 candle specification and ILGOLFE27DC061 golf-ball specification.