Welcome to your crash course in lighting.

Here we streamline a wide world of lighting, to give you just enough information to be able to complete your Lighting Intake. If you do not see your bulb listed it means that we do not offer LED replacements.

In addition to utilizing this guide, we recommend reviewing our Lighting Details Intake Tips sheet.

Light bulbs are designated by letter code, which refers to their shape, and sometimes a number, which refers to its width at its widest point, in eighths of an inch. While there are many shapes of light bulbs — we focus here on the most commonly adapted to LED.

A-shape (A19, A21)

A-Shape (“Arbitrary”) bulbs are likely the first form factor you think of when someone says “lightbulb”.

A19: 2.375 inches in diameter. The standard 60 watt incandescent bulb.

A21: 2.625 inches in diameter. The next most common A-shape, generally being higher lightoutput and wattage.

In the lighting intake platform you do not need to choose a between A19 and A21 as the diameter will be dictated by how much light you need.

CFL (Spiral)

Compact fluorescent light bulbs (CFLs), also known as ‘spirals’ or ‘curly cues’ were the choice for efficiency just a few years ago. CFLs come in most shapes, but internally they all boil down to the spiral fluorescent tube. If you have an exposed spiral, in most cases an A-shape LED is the appropriate replacement. If your CFL is a spiral inside of a PAR 30, for example, then we choose PAR30 as our existing (and new) bulb shape choice, and we note that it is ‘CFL’ in the existing technology drop-down.

LEDs now have far surpassed CFLs in terms of light quality, energy efficiency, lifespan, and value.


Parabolic aluminized reflector (PAR) light bulbs utilize a mirror or reflective surface to focus the light. For LEDs the PAR designation is used to define the shape, as a reflective surface is not required due to the directional nature of LEDs. PAR16: 2 inches in diameter. Less common shape that we do not currently offer.
PAR20: 2.5 inches in diameter
PAR30: 3.75 inches in diameter
PAR38: 4.75 inches in diametercy, lifespan, and value.


Bulged Reflector (BR) or Reflector (R) bulbs are similar in shape to the PAR lamps, but have a rounded (or bulged) lens on top. The rounded lens allows for a more distributed, uniform, light output. The BRs are excellent for general area lighting from ceiling cans or track lights, where you would use the PARs for more directional lighting. The distinction between Rs and BRs does no apply to LED bulbs, so we call them all BRs.
BR 20: 2.5 inches in diameter
BR 30: 3.75 inches in diameter
BR 40: 5 inches in diameter


Multifaceted Reflector (MR) bulbs fit in the palm of your hand and are infamous for producing abundant waste heat and burning out quickly.  The combination of LED MR-16s and old dimmer switches can cause flicker issues.  In most cases this can be fixed by installing an LED compatible dimmer.  Contact us for a dimmer recommendation based on the type of LED bulb you are installing.


Within the B11 shape there are several names and variants such as the flame, candle, and torpe- do, but technically, there are the B shapes (cones), and the CA shapes (candles). The B shape has a bulged base that tapers to a rounded tip and the CA shape rounds to a pointed tip that can be bent to look like a flame. In LED lingo we just call them all B11s, and they can have a ‘flame tip’ or a ‘bent tip’.


G-shaped, or ‘Globes’ are used in a variety of applications where a ball shaped light source is required; such as ceiling fans, bathroom vanities and accent fixtures. G16: 2 inches in diameter. Less common shape that we do not currently offer. G24: 3 inches in diameter. Standard size for vanity fixtures G40: 5 inches in diameter. Less common shape that we do not currently offer.

Base Types
While there dozens of different base types in lighting, we will focus on the most common,and those applying specifically to the bulbs we are addressing.

E26: also known as ‘standard’ or ‘medium base’. The diameter of the base is 1.03″. The most common base type and the one you likely picture when thinking of a light bulb. .

E12: also known as ‘candelabra’ or ‘skinny’ base. The diameter of the base is .47″. This is a common base for the B11 shape.

GU24: also known as ‘2 knobs’. There is a flat base with 2 metal knobs coming out the bottom. The knobs are 24 mm apart. This base is primarily used with A-shape bulbs.

GU10: also known as ‘2 knobs’. There is a flat base with 2 metal knobs coming out the bottom. The knobs are 10 mm apart. This base is primarily used with MR16 shape bulbs

GU5.3: also known as ‘bi-pin’. There are two short needles sticking out of the bottom that are 5.3 mm apart. This base is primarily used with MR16 shape bulbs


The color of light emitted by a bulb (technically called correlated color temperature or CCT) is measured by Kelvin temperature scale. The higher the temperature, the ‘cooler’ the color — or closer to the blue end of the spectrum. The lower the temperature, the ‘warmer’ the color – or closer to the red end of the spectrum. For screw-in light bulbs, the most common choices are 2700K (2,700 degrees Kelvin), or 3000K (3,000 degrees Kelvin), and are the color options we are currently offering. If you are interested in cooler, ‘brighter’, color temperatures you can indicate this on your Facility Lighting Intake and we can try to accommodate.

2700K: also known as ‘warm white’ or ‘soft white’ is warmer and most appropriate for residential, hospitality, restaurants, or any use wanting a more relaxed setting.

3000K also known as ‘natural white’ is cooler and most appropriate for retail, office, schools, and any use wanting a more active setting.

4100K or 5000K: also known as ‘cool white’ is generally used in office, industrial, and educational settings. Overhead light fixtures (troffers, hi-bays, strip fixtures, etc.) tend to the cooler temperatures.

A general note of caution is to beware of relying on terms like ‘soft white’ and ‘cool white’ as there is no industry standard on what term refers to what color temperature, and can vary by manufacturer. Now that you understand color temperature, your best bet is to ignore how the color is ‘named’ on the package and instead look to see what its color temperature, or Kelvin, is.

Beam Angle

The beam angle is presented as a degree, which correlates to the width, or spread, of the light output, and is only relevant for PAR and MR lamps. A narrow beam angle is used to highlight a particular area, like a piece of merchandise or art on display, while a wide beam angle is used for more general illumination.

40D or 38D: 40 degrees and 38 degrees are considered a wide beam angle, or ‘downlight’ or ‘floodlight’, and is far and away the most widely used beam spread and will flood the space with light. The MR16 shapes are generally 38D and PAR shapes are 40D in a floodlight.

25D: 25 degrees is considered a narrow beam angle, or ‘spotlight’,and will focus light on a particular zone or object.