Lumistrips LED Lighting Blog

 When designing, building or installing a UV light, two key questions must be answered first:

"How irradiance does it need to have?"

"What is the required exposure time?"

While there are many studies that show the effectiveness of UV light in disinfection or sterilization, a high variance of the results exists, which presents a challenge to find an answer to these questions. 

We will present our recommendations by analyzing the results of 413 reasearch papers, as found in the compilation "Fluence (UV Dose) Required for up to 99% disinfection from Viruses, Bacteria, Protozoa and Algae"  that can be downloaded at the links below:

PDF: Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae

The research studies present the fluence required to achieve a log reduction from 1 to 5, for different types of UV sources.

The effectiveness of sterilization or disinfection with UV light depends on the exposure, time, wavelength and irradiance.

• Exposure or fluence (sometimes called dose) is measured in mJ/cm² (where 1 mJ/cm² = 10 J/m²)
• Exposure time is measured in seconds (s), minutes (m) or hours (h)
• Irradiance is the flux of radiant energy per unit area, in other words how much of the UV radiation power (measured in W = 1000 “miliwatts” mW = 1.000.000,00 “microwatts” μW ) reaches the surface. Irradiance is measured in mW/cm² or W/m² (1 mW/cm² = 10 W/m²) and is dependent on the radiant power, distance and dispersion of the radiation emitted by the lamp source.

This article is intended as a guide for those who are considering purchasing UVC disinfection equipment. These tips should only be considered as suggestions.

Attention buyers! - There are few recognized standards for equipment designed for UVC disinfection of air and/or surfaces. As a result, there are many advertisements and promotions claiming amazing performance with little or no scientific support.

• Ask the seller for copies of scientific papers that prove that his device actually works as he claims. The scientific work(s) should show the actual reduction of a test micro-organism in the environment in which the device is intended to work. 

• Does the product have suitable built-in UV safety sensors for automatic shutdown or does safe operation depend entirely on the operator?
• Does the device comply with NIOSH, UL, IEEE and related safety standards in the country of sale?
• Does the unit emit/generate ozone? If so, does it meet NIOSH requirements. How is the ozone attenuated? (We recommend avoiding ozone equipment, as it poses a safety risk to operators, unless ozone is specifically part of the treatment process and is used in a controlled and safe manner)?
• Is the device used to disinfect medical devices? If so, is it compliant with the requirements of the regulatory body in the EU, USA or country of sale?

• If the device is a UV rod that is used to disinfect a surface (e.g. a worktop or an envelope)

The technical specifications should state the UVC irradiance at a fixed distance from the UV front of the device (e.g. 10 mW/cm² at 2 cm).

The UV dose (irradiance multiplied by exposure time in seconds) should be at least 20-40 mJ/cm² to inactivate viruses on perfectly flat and ideal surfaces (details in this article). Thus, if the irradiance at the target surface is 10 mW/cm², the exposure time should be 2-4 seconds. However, the presence of microscopic gaps on flat surfaces can inhibit disinfection, and disinfection on other materials, such as cloths, may require completely different doses. For example, disinfection of viruses on medical masks may require doses as high as 1000 mJ/cm^2. This is a subject that is currently being researched and our current understanding changes almost daily.

With any UV device, you must NOT look at the UV light or expose your hands from the UV side. UV light is a source of skin burns/cancer and can quickly damage the eyes.

Remember that UV disinfection is based on a "line of sight" between the UV lamp and the target surface. If the UV rays are shaded by texture elements on the surface, the shaded areas may receive much less UV light or no light at all. Disinfection effectiveness is therefore determined by the UV dose to which these areas are exposed.

Like any disinfection system, UVC equipment must be used properly to be safe.

They all generate different amounts of UVC light in wavelengths from 200 - 280 nm. UVC light is much more energetic than normal sunlight and can cause a severe, sunburn-like reaction on your skin and could also damage the retina of your eye when exposed.
Some devices also produce ozone as part of their cycle, others produce light and heat like an arc welder, and still others move during their cycles. In general, all disinfection devices must therefore take into account the safety of both man and machine.

These considerations should be taken into account in the operating manual, in user training and in compliance with appropriate safety regulations.

As a manufacturer, we aim to use the top performing LEDs in our LED strips and modules. We are particularly focused on mid power LEDs, those that usually use less than 0.3 Watt of energy, are fairly small and require minimal or no cooling. A big share of our products use these LEDs.

Before choosing the best performing LED for our products we have compared more than a dozen models from the top LED manufacturers: Nichia, Osram Opto Semiconductors, Samsung, Philips Lumileds, LG Innotek, Seoul Semiconductor, Cree, Everlight.

For a meaningful comparison we selected LEDs that function at 65 mA with a voltage between 2.75 and 3.2 V, classified in three groups:

• Cold White (5000-6500K), CRI 80+, for linear fluorescent replacements (LED tubes) or lighting fixtures for the office or industry
• Warm White (2700K-3900K), CRI 80+, usually used in LED lamps, linear lighting fixtures, cove lights, desk lamps, usually for residential and hospitality sectors
• Warm White (2700K-3900K), CRI 90+, with applications in luxury lighting, professional linear lighting fixtures, cove lights for commercial and hospitality sectors

For each category we compare the luminous flux and luminous efficacy at the usual junction "lab temperature" of 25ºC and at a more realistic 100ºC. The comparison data is that from the manufacturers datasheet.

We also added the performance data of average 5050 and 3528 LED packages because such LEDs are still used by many lighting manufacturers today, with applications including linear led modules, fluorescent tubes, lamps, panels or even luxury lighting fixtures.

Cold White (5000-6500K), CRI 80+, for LED strips and modules for the office or industry.

Nichia 757G LEDs have the highest performance and efficacy at 25ºC and 100ºC, with 37.5 lumen and 210 lumen / watt and 33.75 lm and 189 lumen / watt respectively. They also have the lowest performance difference between "lab" and "reality" operating temperatures, at only 10%.

Effective and cost efficient disinfection or sterilizing of surfaces, water and objects can have a significant, positive effect on the general health of our society. The impact of pandemics, present such of the COVID-19 (coronavirus), and future can be greatly reduced, as well as a major decrease of illnesses in general, including from drug resistant pathogens or hospital-acquired infections (HAI).

Disinfection or sterilization with ultraviolet (UV) light can be the way to achieve such goals. However, challenges of using UV light still exist and the ways to overcome them are presented in this article.

Using ultraviolet (UV) light to disinfect or sterilize¹ has actually been embraced by some hospitals since years, by using large, industrial-grade machines to kill microorganisms (including COVID-19) in hospital rooms or on furniture, objects, clothing or instruments. However, such machines are the perfect showcase of the challenges of using UV light. They are prohibitively expensive for private or business use, as a mobile platform with UV lamps can cost more than 60.000 USD². Their deep UV radiation is also dangerous for people and must be used only in empty rooms.

With the current advances in UV LED lighting technology both problems can be overcome.

Smaller versions of UV disinfection lamps can be built at affordable cost, so they are accessible to consumers and companies looking to clean pretty much everything, from office spaces, elevators and living rooms, to phones, computers and even toilet seats.

Different UV wavelengths with precise control of intensity and radiation pattern can make disinfection safe to be used when people are present.

The most promising practical application of the above is the continuous disinfection with low intensity UVA LEDs .

*Irradiance limited to 10W/m² at 2m from the floor.

**According to two independent studies quoted in this article.

Growing plants in closed and fully controlled environments, under artificial lighting is method of growing popularity, with increasing competition to have results at a low cost and as fast as possible. Thus the lighting system plays a crucial role.

Below you will find a quick guide how to build the most efficient lighting system.

1) Research, research

Discover what spectrum and intensity of light your plants need.

You can start by reading our detailed article about horticulture lighting here

2) Choose the right PPFD and light color for your plants

By using the latest technology, special or full spectrum white light LEDs have become the most efficient and cost effective light sources for plant growth. 

With our Nichia 757 Rsp0a LEDs with white light for special spectrum for plant growth or full spectrum Nichia Optisolis CRI98 LEDs your plants will grow up to 50% more than conventional light, including standard white LEDs, a combination of red and blue LEDs or a fluorescent tube, for lower energy consumption.

With 3000K white color temperature you will have more pleasant looking plants while with 5000K you obtain faster growth.

Industrial scale indoor agriculture under artificial lighting in closed and fully controlled environments could become the main factor that keeps at bay famine and related conflicts. With increasing population, diminishing area of agricultural land, pollution, global warming and migration to grow plants in a reliable, predictable and efficient way will become even more important in the future. For this reason it is important to understand and corectly apply the concepts of lighting for plant growth and development.

Concepts related to Horticulture lighting

A key factor in the success of indoor plant growth is the efficiency of the lighting system compared with sunlight, in the process of plant growth.

Plants grow via a process called Photosynthesis that converts electromagnetic radiation (light) into the chemical energy needed for growth and development. The other ingredients required are carbon dioxide (CO2), nutrients and water. 

Photosynthesis and PAR radiation

The electromagnetic radiation required for Photosynthesis is defined as photosynthetically active radiation (PAR) and 400 to 700 nanometers has spectral range. Only radiation in this interval can be used by photosynthetic organisms in the process of photosynthesis, to fix the carbon in CO2 into carbohydrates.

Electromagnetic radiation called visible light or simply light for a typical human eye has a spectral range from about 380 to 740 nanometers.

A common unit of measurement for Photosynthetically active radiation PAR is the photosynthetic photon flux (PPF in short), measured in units of moles per second. For many practical applications this unit is extended to PPFD, units of moles per second per square meter.

The theory behind PPF is that every absorbed photon, regardless of its wavelength and energy, has an equal contribution to the photosynthetic process. As in accordance with the Stark-Einstein law, every photon (or quantum) that is absorbed will excite one electron, regardless of the photon’s energy, between 400 nm and 700 nm. 

However, only some of photons are absorbed by a plant leaf, as determined by its optical properties and the concentration of plant pigments. The pigments are Chlorophyll A, Chlorophyll B, and Carotenoids (a/-Carotene, Lycopene, Xanthophyll).

The Chlorophylls A and B give plant leaves the characteristic green color because they reflect most of the radiation between 500 and 600 nanometres.  Plants Where more Carotenoids than Chlorophylls are present plant leaves reflect wavelengths beyond 540nm and have yellow, orange, and red colors. This includes autumn leaves when Chlorophylls have dried away. 

The graph below shows the typical absorptance spectra for Chlorophyll A, Chlorophyll B and Chlorophyll (beta-carotene). Each are explained briefly afterwards:

According to the standard EN 12464 Light and lighting - Lighting of workplaces -Indoor work places, the light level recommended for office work is the range 500 - 1000 lux - depending on activity. For precision and detailed works the light level may even approach 1500 - 2000 lux. For ambient lighting the minimum illuminance is 50 ulx for walls and 30 lux for ceilings.

Recommended light levels for different types of work spaces are indicated below:

Read more about recommended lighting levels for the home in our blog article.

The CRI, colour rendering index, is a one-number quantification that indicates the performance of an artificial light source in terms of colour rendering compared to a reference standard light source modelled on daylight. The highest number is 100, for daylight and incandescent/halogen lamps, while gas discharge lamps range from 17 to 96, with even a negative value for low sodium pressure (the yellow type used in street lamps).

Due to this variation in the ability to reproduce colour with the white light emitted by the many types of gas lamps on the market, CRI index was introduced in 1974 by the International Commission on Illumination (CIE). 

Today, with more than 40 years of use, the CRI index is firmly rooted in the lighting industry and among professionals. However, it has not been very well understood by the public. The reason was that such knowledge was not really useful as most lamps were built for specific applications that required a minimum CRI value, so one could not go wrong when choosing a lamp.

For example, for office or other linear lighting, the lamps of choice where Tri-Phospor linear fluorescent tubes on the market since the 1970s, all with a CRI value above 80. For domestic lighting, there was a mix between incandescent and halogen lamps, both with CRI100, for retail and other high intensity spot lighting, metal halide lamps with CRI min 85. Street lighting was reserved for high intensity and very efficient sodium vapour lamps, which had a poor CRI but this was considered not important.

From the year 2000 this changed with LED technology, the first light source that can be used for any application while having a broad performance and quality level, including the ability to reproduce colours accurately. It is therefore essential that you choose LEDs with the right CRI level for your application.

The picture above shows how colors can look different based on the CRI of the light source that illuminates them. A vibrant red under sunlight or a high CRI light can look dull or even orange under a low CRI light.

Lines of light are a new trend in lighting design and are usually made with an LED strip inside an aluminum profile that has a translucent white cover. The attraction of using such a linear light fixture is that it can be personalized. You can choose as you desire the pattern, place of installation, length (up to many meters), geometric shape or a combination of these elements.  

Because of their way of construction lines of light are a type of direct lighting. Compared with coves that are indirect lighting, lines of light are more energy efficient but can have greatly increased glare. For this reason lines of light should be designed with care and almost always be dimmable. 

Let's see how we can achieve the best results with lines of light.