Calculating Light for Your Space

Class 2  -  Wires


Class 2  -  Power Supply


Cool lighting is associated with attentiveness and movement making it better suited in bathrooms, kitchens and exteriors. Cool colors are generally preferred in hospitals, schools and other commercial applications where you want people alert and attentive. Studies continue to surface confirming that blue (cool) lights activate and excite the brain while red (warm) lights relax the brain.

Unlike regular 120V wires (12-14gauge) that are used to wire most things in your home, 12V & 24V wires (18-24gauge) have a wide variety of uses outside of construction. As a result, wire manufacturers produce wires with different levels of protective sheathing. Class 2 wiring costs a little more to produce but is considered safe to install behind drywall making it ideal for LED applications with remote power supplies. Your building inspector will look for the “Class 2” markings printed on the wire.


CRI is relatively important when evaluating different fluorescent and LED lamps and fixtures. An LED with a 95CRI should theoretically be better than an LED with an 80CRI of the same color temperature. It's important to understand that LED technology has one of the biggest obstacles in rendering all perceivable colors accurately, as diodes in LED lights each have their own narrow wavelength of color production. This is in contrast to incandescent that already emits a wide spectrum of colors. A high CRI is important in locations such as bathroom mirrors, retail displays and anywhere that you want illuminated objects to look alive and vibrant. Higher CRI always comes with a higher price tag because of the extra production costs involved.

R1 - R8

Footcandles (Fc)

The environment of a space determines how intensely lit it should be. A retail space typically has products for sale that should all be well lit so they are clearly visible to customers. This is also true for kitchens, offices and warehouses where visibility is a priority. On the other hand, bedrooms and bathrooms should have less bright, more diffuse light. The table to the right gives some basic recommendations for fcs in a functional space.


Class 2 compliance is a regulatory measure meant to reduce fire hazards in low voltage systems. In lighting this is important for 12-V and 24-V LED systems that use a remote power supply.

A lumen is the light output, or intensity, produced by your fixture or lightbulb. You can find the total lumen output of a given light fixture on the manufacturer specification sheet.


Footcandles are units of measurement that describe how many lumens your lightsource will cast on the surface of your space. One footcandle equals one lumen per square foot.

This is the lighting that gets the job done! In kitchens and bathrooms this might be a recessed downlight over the sink or counter or under cabinet lighting. In an office it might be track lighting or a desk lamp. Just like the name indicates, task lighting helps you complete tasks!

Adjustable recessed spots, opaque wall sconces and track lighting can often play this role. Accent Lighting is almost the opposite of functional lighting. It's purpose is solely to dramatic or striking. A key feature to this type of lighting is the use of shadows and darkness (between light sources) to create a scene for the onlooker.

After you've determined how many footcandles would be ideal for your space you can start thinking about what and how many fixture(s) would be appropriate. This is especially important for commercial spaces where employees need to work and customers need to make purchases. The goal is to strike a balance between 'too bright to feel comfortable' and 'too dark to see anything'

Before you start choosing a fixture, you need to find the total square footage of your space. This will be used with the desired average number of footcandles to determine fixture quantities and type. A parking garage may function better with fewer, more intense spotlight type fixtures over the car parking spots. A warehouse would function best with more fixtures that provide very diffuse, bright light.

Warm lighting is easier on the eyes and is best used in bedrooms, reading areas and any area designated for relaxation. Incandescent and Halogen light sources naturally produce this warm color and still have the best dimming performance. Red light is the longest wavelength among colors in the visible spectrum (630-700nm). This makes it the least disturbing to the human circadian rhythm and brain function. Traditional Black & White photography dark rooms can only use red light to avoid exposing pictures. Florida has guidelines mandating a red or amber light to protect sea turtles and other marine life.

The Kelvin Scale is used in lighting to denote the color of a light source. The color of a light source plays a huge role in how we perceive illuminated objects and surfaces. The lighting industry is concerned with the visible range from approximatly 1800K (Candlelight) to 7500K (Daylight).

Class 2

Blues, Greens, Silvers, and Grays are considered “Cool” colors.
Cool White is roughly 4000-7500 Kelvin.

Types of Light

CRI stands for Color Rendering Index which denotes how accurately a light source renders colors. The scale is from 0CRI (certain types of H.I.D.) to 100CRI (natural light from the sun). The basic concept is that the higher the CRI the easier it is to identify different shades of colors. However, a higher CRI alone doesn't necessarily equate to more accurate colors because they're also affected by color temperature (see Kelvin scale).

For a low voltage power supply to be Class 2 compliant a 12-volt driver must not exceed 60 watts per tap and a 24-volt driver must not exceed 96watts per tap. If your project load calculation requires more than these figures you have two options: Option A) Use several individual drivers. Option B) Use a higher wattage “multi-tap” driver. A multi-tap driver has separate ports for each LED load theoretically reducing the fire hazard by reducing the concentration of power. For example, a 120W multi-tap driver might have two 60W ports so that you can run two 60W circuits from the same driver.

CRI (Color Rendering Index)

General Retail
Retail Display
50-80 ambient

Educational Tools

Color Temperature (Kelvin Scale)

Reds, Yellows, Golds, Browns, and Oranges are considered “Warm” colors. Warm White roughly equates to 2000-3800 Kelvin.

Ambient Lighting tends to have a light source that illuminates 360degrees. The best example is an incandescent pendant that radiates light from all angles. It creates a glow that is less ideal for tasks but creates a very pleasant environment.

Warm Colors

Images sourced from Pexel, 2019.

​​T. Haynes Lighting

Cool Colors

Serving the Bay Area since 1997

Lighting Design Example:

R9 - R14

Let's say you want to know how many fixtures to purchase to light a general retail shop that is 100' x 50', or 5,000 sq.ft. The chart recommends an average of 35 fcs for this type of space. The fixture you are interested in has an output of 15,000 lumens, per the manufacturer specification sheet. Plug these values into this formula:

(Total square footage x Desired fcs) / Total Fixture Lumen Output = # of Fixtures

(5,000 x 35) / 15,000 = 11.66 fixtures

You would end up needing about 12 fixtures to light the retail space.