Quick answer: A BR30 is a bulged-reflector flood bulb whose size designation means 30 eighths of an inch across: 30 ÷ 8 = 3.75 inches. The diameter comes from the federal BR30 definition, and the flood-light classification appears in Wikipedia's bulb-shape table.
The code helps identify shape and width. Choosing a replacement also means separating those dimensions from the base, light output and controls. This guide explains the designation, compares the larger alternative, and shows how to use dimensions without mistaking them for a brightness rating.
What do the letters and number mean?
BR means bulged reflector; the number identifies diameter in eighths of an inch. According to the federal definition of a BR incandescent reflector lamp, the bulge lies below the bulb's widest part and above its approximate base line. The same regulation defines BR30 specifically as an incandescent reflector lamp with a diameter of 30/8 inch.
The arithmetic is straightforward:
- Diameter in inches = designation number ÷ 8 = 30 ÷ 8 = 3.75 inches.
- Diameter in millimetres = inches × 25.4 = 3.75 × 25.4 = 95.25 mm.
That metric result is an exact conversion of the nominal inch figure, not a manufacturing tolerance. Wikipedia's shape table lists a primary figure of 95 mm for the corresponding diameter and lists the metric designation as BR95 E26.
According to Wikipedia's explanation of bulb designations, letters identify shape and numbers identify a characteristic size. Its reflector categories include standard reflector R, bulged reflector BR, and elliptical reflector ER. Those are shape distinctions; do not read the letter combination as a performance grade.
Is BR30 the same thing as E26?
No: BR30 describes the bulb envelope, while E26 describes the screw base. Wikipedia's BR30 E26 entry pairs the flood-light shape with a 26 mm Edison screw base. The wider bulb body and the narrower threaded base are separate dimensions.
Read a replacement listing in separate parts: shape, base, overall dimensions and electrical ratings. A matching base answers the socket question, but it does not establish whether the wider body clears the fixture opening. Likewise, a matching shape does not establish the supply rating or suitability for a particular control.
For a recessed fixture, compare the actual bulb dimensions with the available opening and depth. Our guide to measuring recessed lighting helps distinguish the opening from the surrounding trim. Measure straight across a circular opening through its centre; a tape wrapped around the edge measures circumference, not diameter.
How much larger is BR40 than BR30?
BR40 has a larger nominal diameter, while retaining the BR shape designation. According to the federal BR40 definition, its diameter is 40/8 inch. The table compares that definition with the regulation's BR30 size; the metric values are unit conversions.
| Shape | Nominal diameter calculation | Metric conversion | Practical comparison |
|---|---|---|---|
| BR30 | 30 ÷ 8 = 3.75 in (source) | 3.75 × 25.4 = 95.25 mm | Smaller bulb diameter |
| BR40 | 40 ÷ 8 = 5 in, according to eCFR | 5 × 25.4 = 127 mm | Larger bulb diameter |
The diameter difference is 5 − 3.75 = 1.25 inches, or 1.25 × 25.4 = 31.75 mm. This calculation compares widths only. It does not establish a brightness difference, beam-angle difference or dimming advantage.
Worked example: assumed opening and bulb dimensions
Assumed inputs: a circular fixture opening measured at 4.5 inches, a smaller candidate bulb measured at 3.75 inches, and a larger candidate measured at 5 inches. Assume each bulb is centred in the opening. These are illustrative measurements, not a fixture recommendation or a required clearance.
- Total width remaining = opening diameter − smaller bulb diameter = 4.5 − 3.75 = 0.75 inch.
- Gap on each side = total width remaining ÷ 2 = 0.75 ÷ 2 = 0.375 inch.
- Larger bulb's excess width = larger bulb diameter − opening diameter = 5 − 4.5 = 0.5 inch.
The smaller candidate clears this opening geometrically; the larger one cannot pass through it. Neither calculation establishes complete fixture compatibility: it leaves overall length, socket position and any specified clearances unresolved.
What changes when the bulb uses LEDs?
Compare LED replacements by light output and power separately. Lumens describe total visible light output; watts describe electrical power. Use the bulb comparison tool to compare lighting options, then use the actual candidate's ratings for your purchase decision. There is no watts-to-lumens conversion supplied by the BR shape designation.
ENERGY STAR explains that LEDs emit light directionally, unlike incandescent and CFL sources. That makes directional lighting a relevant consideration when comparing reflector-style replacements. It does not supply a particular beam angle for every bulb carrying the same shape code.
Lifetime also needs a precise definition. According to ENERGY STAR's LED explanation, LED lifetime is based on a prediction of when light output has decreased by 30%, rather than simply when the lamp burns out. Remaining output at that point is 100% − 30% = 70% of initial output. That is an output threshold, not a promised number of operating hours for your chosen bulb.
What should you compare before buying?
Start with shape and fit, then compare the lighting result. The BR30 E26 reference entry describes a flood-light shape with a 26 mm screw base; neither figure states how many lumens the product emits.
- Fit: match the requested shape and base, then compare bulb width and overall length with the fixture.
- Output: compare the stated lumens with the output you want, and compare power separately in watts.
- Distribution: compare the stated beam information with the area you want illuminated. Do not substitute the shape number for an angle.
- Appearance: compare colour-temperature and colour-rendering information between the candidates.
- Controls and location: confirm the selected bulb's stated dimming compatibility and fixture-use restrictions before buying.
If replacement involves changing mains wiring or the fixture's electrical connections, use a qualified electrician.
FAQ
What does BR30 stand for?
BR means bulged reflector; according to the federal definitions, the BR30 incandescent reflector designation specifies a diameter of 30/8 inch, or 3.75 inches. It identifies a shape and size, not a lumen rating.
Is BR30 a flood bulb or a spotlight?
Wikipedia's bulb table classifies BR30 E26 as a flood light. Use the individual product's beam information when choosing coverage; the code alone gives no numerical beam angle.
Does BR30 mean it has an E26 base?
The reference table lists BR30 with an E26 base, meaning a 26 mm Edison screw. Treat the shape and base as separate entries when matching a replacement.
Can I replace BR30 with BR40?
Do not assume it will fit: according to eCFR, BR40 is 40 ÷ 8 = 5 inches across, compared with BR30 at 30 ÷ 8 = 3.75 inches. Compare the available space and the replacement's other ratings before making that substitution.
Does a larger bulb automatically give more light?
The federal BR30 and BR40 definitions distinguish their diameters, not a fixed difference in light output. Compare the candidates' lumen ratings instead of inferring brightness from their widths.
Jack Shi
Founder & editor, LEDaskJack Shi builds and writes LEDask, an independent LED-lighting tools project operated by clooms. He designs the calculators, checks their formulas and reference values against published engineering data, and writes the guides across the site.
