Each BioWall will require a custom lighting solution dependent on:
- The amount of natural light available
- The dimensions of the surface to be lit
- Species of plants to be grown
- Architectural aesthetics of fixtures
Horticultural Lighting Calculations
Use of Natural Sunlight
Use of Artificial Light to Light a BioWall
In many buildings, little or no natural sunlight is available to illuminate a living wall.
Determining The Need For Artificial Lighting
If your space receives any sunlight, or if you are considering designing or selecting a space for a living wall, explore the information on this page for natural lighting to begin to get a conceptual sense of likely and unlikely acceptable lighting scenarios.
If the space exists, we can measure the light intensity and quality, then calculate PPFD and DLI to confirm and quantify whether artificial light is needed.
If the space does not exist, we can estimate the need for artificial lighting. If in doubt, install the required electrical circuit and conduit, which is relatively inexpensive during construction, but can be very costly as a retrofit. Once the space is framed and glazed, we can measure lighting and make a final determination before the BioWall is installed.
Selecting Lamps and Fixtures
First, we should determine the intensity and spectrum of light needed. Then we can collaborate with the lighting designer on fixture selection that balances horticultural and aesthetic needs. Alternately we can provide full lighting design services.
Living wall lighting technology is rapidly evolving, and we work closely with the leading manufacturers of this technology. We considered posting a shortlist of our most reliable living wall lamps and fixtures on this page, but each time we tried, some were discontinued, and some improved models had just been released. So we are staying on top of the state of the art to assist individual customers for individual projects.
Very few architectural lighting manufacturers test lamps for horticultural performance, and very few “grow lights” are acceptable for architectural use. We regularly test fixtures to determine performance.
It is important to confirm as-built lighting performance upon installation and through time. Most lamps lose efficiency over time. We take regular light readings post-installation to ensure that light levels continue to be sufficient. Even when lamps appear to produce light levels similar to new lamps, the lamps might require replacement if adequate PPFD is not being delivered to the wall.
BioWall Lighting – Natural Sunlight
All plants – including living walls – are ideally lit with natural sunlight. Whenever practical, we prefer to site BioWalls in locations where they can thrive in natural daylight without artificial lighting. No artificial lights can quite match the spectrum, intensity, and energy efficiency of natural sunlight. This page is a conceptual overview of four strategies (atria, skylights, clerestories, and sometimes windows) to light living walls via natural light
Note: The ideas shown on this page are conceptual, and that any lighting design for natural or artificial light requires calculation and verification of PPFD and DLI
An atrium is a wonderful place to locate a BioWall. Continuous ceiling glazing allows capture of the sun’s rays at a wide variety of solar angles. Often the intensity of this light refracts off the floor and other surfaces to create increased light intensity at the BioWall. Three of our most vigorously growing BioWalls are located in atria, as shown below.
BioWall in a brightly lit atrium, soaking up natural light from overhead glazing, as well as three-stories of south-facing glazing
BioWall on a north-facing wall in a five-story atrium with skylights, north- and west-facing glazing
BioWall in a four-story atrium with overhead glazing and south-facing glazing
For maximum light utilization, locate a skylight on a high curb (say 24 inches +/-) directly above the BioWall, for the full length of the BioWall. If the inside face of the curb is reflective (such as white-painted drywall), light should refract off the curb to illuminate the BioWall during low sun angles and from two directions. Adequate light may reach the bottom of the BioWall, depending upon the height of BioWall, height of curb, and skylight glazing.
A skylight on a low curb directly over the BioWall, for the full length of the BioWall will likely allow sunlight to reach closer to the bottom of the BioWall when the sun is at a high angle. However, without the reflective surface of the high curb, sunlight is less efficiently captured from one side of the skylight. If skylights will be used on low curbs, the skylights might need to be larger than if used on high curbs.
A skylight does not need to be directly over the BioWall to be effective, but distance of skylight from BioWall will decrease the intensity and spread of sunlight reaching vegetation. The top edge of the BioWall may fall into shadow, and the bottom of the BioWall may be less intensely lit. Some supplemental artificial lighting can be used to illuminate these dimmer areas of the wall.
In the example above, a 15-foot tall wall is lit entirely by a skylight on a high curb immediately above the BioWall. The skylight only spans approximately three-quarters of the BioWall length, so very low light plants are used in the top right corner.
A very effective way to capture natural sunlight is to locate a clerestory on a high curb (say 24 inches +/-), directly over the BioWall, for the full length of the BioWall. If the inside face of the curb is reflective (such as white-painted drywall), light should refract off the curb to illuminate the BioWall during low sun angles and from two directions. Adequate light may reach the bottom of the BioWall, depending upon the height of BioWall, height of curb, and clerestory glazing.
As with skylights, clerestories lose effectiveness as they are sited farther from the BioWall. The top edge of the BioWall may fall into shadow, and the bottom of the BioWall may be less intensely lit. Some supplemental artificial lighting can be used to illuminate these dimmer areas of the wall.
The BioWall shown above is a 25-foot tall BioWall located directly beneath a clerestory on a high curb. Notice how brightly lit the top of the wall is, and notice dappled light extending approximately two-thirds down the wall. Only the bottom five +/- feet of this BioWall requires supplemental lighting.
In this view of the BioWall, notice that sunlight reaches the bottom of the wall, when the sun is at a high angle in the sky. As clerestories only allow light in through the sides, lower portions of BioWalls lit by clerestories may require supplemental light, as direct light occurs very few hours in the day.
A window or curtain wall may be used to illuminate a BioWall, if the glazing height spans most or all the height of the BioWall and is located immediately adjacent to the BioWall. But this treatment is generally only effective within approximately 10 feet of a very sunny window with no window treatments. Areas of potential shadow include the top edge of the BioWall, if higher than the top of window.
Even very large windows are generally ineffective at capturing sunlight to light BioWalls, unless they are sited immediately adjacent to the BioWall. In the drawing above, most of the room has inadequate photosynthetic light, and minimal photosynthetic light reaches the BioWall.
Small windows are generally ineffective at capturing sunlight to light BioWalls, no matter how close they are to the wall.
Windows facing BioWalls are generally ineffective at capturing adequate sunlight, unless those windows are within approximately 5 feet of the BioWall.
This small BioWall (approximately 12 feet wide x 8 feet tall) is lit entirely by a 15-foot-tall x 15-foot-wide west-facing sunny window. This is one of the few arrangements in which a window is large enough and close enough to effectively light a BioWall.
Living Wall Lighting Calculations
If you are less familiar with calculating horticultural lighting requirements, use this page as you prepare a custom lighting solution for your BioWall project. We start with daily light integral (DLI), which is essentially the plants’ need for an intensity and quality of light over the course of a day. Next, key lighting terms further defines DLI and some of the terms used to calculate DLI, and we describe how to determine acceptable DLI. Because the lighting solutions above include a limited number of fixtures and lamps, we include some footcandle to PPFD conversions for lamps without established PPFD ratings. Quality control is covered, as lighting design is so critical, and requires care in design and verification. Finally, we address light timing.
Introduction to Daily Light Integral
The light spectrum that plants use for photosynthesis overlaps the spectrum visible to humans, but it is not the same spectrum; therefore designing lighting for interior vegetation is critically different from traditional architectural lighting design. The light spectrum visible to humans ranges from 400 nanometers to 700 nanometers. Plants cannot use light in the green portion of the visible light spectrum (around 550 nanometers). This is why plants appear green to the human eye – plants cannot use this light, and therefore they reflect it.
The portions of the visible light spectrum that plants can use is called photosynthetically active radiation (PAR). PAR can be measured with specialized light meters, and many lighting manufacturers can provide information regarding the spectral quality. The Daily Light Integral (DLI) is a measure of the density (intensity) of PAR delivered per day. The primary objective in BioWall lighting design is to provide an appropriate DLI.
Definitions of Key Lighting Terms
Footcandles (FC): A measure of the intensity of light, commonly used in designing light that is visible to humans.
Lux: A measure of the intensity of light, commonly used in designing light that is visible to humans.
Color temperature: A measure of the color spectrum provided by light, expressed in degrees Kelvin (K). Warm color temperatures (yellowish-white through red) are in the range of 2,700-3,000K, while cool color temperatures (bluish white) are in the range of 5,000K.
PAR: Photosynthetically active radiation. PAR is light that is available to plants for photosynthesis, and is generally maximized in the “red” (2,700K and less, around 700 nanometers) and “blue” (5,000K and higher, around 450 nanometers) color spectra. PAR is lowest between 500 and 600 nanometers, or around 4,000K, the spectrum most visible to humans.
PPFD: Photosynthetic Photon Flux (area) Density. A measure of the density of PAR that will fall on a surface, expressed in µmol/ m2/s (micromoles per square meter per second).
Daily Light Integral (DLI): A measure of the PPFD delivered to square meter per day, expressed in mols/m2/day.
Determining Acceptable DLI
The first step in BioWall lighting design is determining the wall’s DLI requirements. DLI requirements vary by plant species, but the plants used in most BioWalls prefer a DLI from1.5 to 4.0. The minimum acceptable DLI for any portion of a BioWall is 1.5 with a minimum PPFD of 35.
Having determined the target DLI for the BioWall, calculated the PPFD needed, which will be used to determine light intensity. Start by assuming that light will be uniformly delivered over 12-hours per day, which most closely simulates the equatorial climate to which most tropical plants are adapted. Though the duration of light may be raised or lowered from 12 hours per day, exercise caution, as 12 hours per day is ideal to provide adequate lighting and adequate rest periods for long-term optimal plant health.
DLI = PPFD * hours * 3600 / 1,000,000
Rearrange the above equation to solve for PPFD:
PPFD = DLI / (hours * 3600 * 1,000,000 )
For example, if targeting a DLI of 2 over 12 hours, we calculate that we need a PPFD of 46.
Footcandle to PPFD Conversion (For Lamps Without Established PPFD Ratings)
If you are using a lamp that has not been designed for horticultural purposes, the lamp’s intensity will likely be documented in FC, versus PPFD. Below are general conversion factors for foot candles to PPFD for the most common types of artificial light sources, which can be used in determining whether a lamp might deliver appropriate PPFD. As conversion factors vary, use manufacturer-specific conversion factors whenever available. Because light intensity varies based on distance from the lamp, obtain the lamp’s FC distribution curve or a photometric analysis of the proposed wall with the proposed lamps, then multiply FC by the conversion factor to calculate PPFD. Please note – there is not yet a proven, accepted conversion factor for FC from LED-based lamps to PPFD, but we can provide PPFD measurements for select LED lamps.
|Cool White Fluorescent Lamps||0.146|
|High Pressure Sodium Lamps||0.131|
|Low Pressure Sodium Lamps||0.102|
|High Pressure Metal Halide||0.152|
|Plant Growth Fluorescent (Gro-Lux) Lamps||0.326|
|Incandescent 100 W Tungsten Halogen||0.215|
Lighting Design Quality Control
After following the process above (determine DLI needs, and select/site lamps to deliver PPFD to meet the DLI needs), check the lighting design to ensure the following are met. If any of the following are not met, revise the lighting design.
- Number of hours used in PPFD to DLI conversion is as close to 12 as practical.
- No areas of the BioWall receive less than 1.5 DLI.
- Lamps are sited far enough from the wall to avoid burning foliage. In general, higher intensity lamps will be required to illuminate farther from the lamp, but lower intensity lamps may be used in closer proximity to the BioWall. Refer to safe heat distance ratings for each lighting solution.
- Lamps are sited such that they can be aimed at all areas of the wall effectively without plants casting shadows that blocks light from reaching other areas of the wall. (This is primarily a concern when using large foliage plants and/or when fixtures are aimed such that they “graze” the wall.)
- Lamps are sited to illuminate from above or from directly in front of the BioWall to the extent practical. Lamps that illuminate the BioWall from below the vegetated surface may cause leaves to turn downward toward the light, which causes no horticultural problems, but can look “odd.”
As noted above, the duration of the lighting regiment should be as close to 12 continuous hours of provided light over a 24 hour period to simulate the daylight of a near equatorial locale. Lights should be powered by a timer in a locked box that will be readily accessible to maintenance personnel. Timer settings should have only one “on” and only one “off” cycle per day. For example, the lights should not be on an alternating 3 hours on/ 3 hours off schedule. While this would meet the “12 hours over a 24 hour period” minimum, plants are very sensitive to day length and a new day “starts” each time the lights go off. The 12 continuous hours can be at any time during the day or night.