Material related questions Q: Stainless steel is the prefered material for conventional lighting in NPPs. Why don’t you use it? A: Because stainless steel is not suitable for LED Lighting. The main reason is very poor thermal conductivity of the material. Heat is number one killer (beside the radiation, of course) of any electronics and drastically reduces the lifetime of the product. Keeping operational temperature as low as possible has always been our main design goal. Q: What is thermal conductivity? A: Thermal conductivity is the ability of the material to conduct heat. It is measured in W/mK. Here are some thermal conductivities in W/mK: Air: 0.02 Wood: 0.04 Concrete: 0.8 Stainless steel: 16 Iron: 80 Aluminium: 200 Copper: 400 Diamond: 1000 From the table above it can be seen, that the stainless steel has poor ability to conduct heat. In fact, the ability of stainless steel to conduct heat is one of the worst in metals. This is the obvious reason, why we do not use stainless steel for our LED Luminaires. Q: Did you try to make a LED Luminaire in stainless steel housing? A: Yes, we tried. We tested the same Luminaire housing made out of copper, aluminium and stainless steel. Stainless steel did not pass the test. Q: You can compensate bad thermal performance of the stainless steel by adding more cooling fins, right? A: Wrong. You can add stainless steel cooling fins to infinity without results. The only effect is heavy, bulky product, without proper cooling. Q: What is emissivity of the material? A: Emissivity is the surface property of the material. It shows the ability of the material to exchange heat energy with the surrounding media. Any glossy finish of the heat sink material has bad emissivity and therefore slow exchange of the heat energy with the surrounding air. An aluminium foil (glossy finish) has emissivity coefficient of 0.04, while anodized aluminium has the emissivity of 0.8. In both cases the same material regarding thermal conductivity, but anodized one has 20 times better emissivity, i.e. exchange of the heat with the surrounding media. Q: Aluminium is not allowed in areas where hydrogen can be the problem. How do you solve this problem? A: For demanding nuclear applications we use pure electrolytic copper as the material of choice. Copper is in fact very common material used in any NPP. It has excellent thermal properties, 25 times better then stainless steel. The only disadvantage is weight. All our products are available in two versions, a copper and an aluminium version. The main advantage of aluminium is much lower weight and is prefered choice of material in less demanding nuclear applications.
Radiation related questions Q: Do you test your products with radiation source, or you just compile public documents describing radiation hardness of electronics? A: We allways test our products and never assume anything. All our products have full nuclear qualification and tests, performed by third party certified laboratories. Q: Which part of your Luminaire is tested to radiation? A: Each and every part of our product is tested with gamma and neutrons. This includes all mechanical parts (housing, screws, optics, diffuser, sealings, coatings, connectors, wires etc) and all electronic parts including LEDs and complete LED control gear (driver). Q: Where do you test your products and components? A: All our products are tested inside the core of General Atomics TRIGA Mk II nuclear research reactor in Jožef Stefan Institute, Reactor Infrastructure Centre in Ljubljana, Slovenia, EU. In case of gamma irradiation, the nuclear reactor is shut down, without presence of neutrons. In case of neutron irradiation the research reactor is operating normally. Q: Which part of LED Luminaire is the most problematic one regarding radiation? A: LED control gear (driver) is by far the most problematic part of any LED Luminaire. Q: Your electronics is not affected by gamma and neutron irradiation. Why? A: Every electronics is affected by the radiation, including ours. We achieved world’s best radiation hardness in LED lighting industry with careful selection of components and circuit topology, cancelling the effects of radiation damage. Q: Many producers of LED Luminaires are testing just LEDs to gamma. Is this correct? A: No. The LED itself is relative insensitive to radiation, opposed to power electronics which might be up to 1000 times (three magnitudes of order) more sensitive. Testing LEDs only and assuming the Luminaire has the same radiation hardness as LEDs, is not true. Q: Do you irradiate your electronics biased? A: Of course. Our electronics (complete functional PCB) is irradiated biased, i.e. up and running at full power before, during and after the test. Irradiation of unpowered or unbiased electronics, or even components alone, not installed on PCB, gives wrong, misleading result - a magnitude better then biased. Q: Do you use 60 Co for gamma tests? A: No. For gamma and for neutron irradiations we use TRIGA Mk II Nuclear Research Reactor. Nuclear reactor has similar gamma spectrum to NPPs and better mimics real world situation inside containment. Q: Is your LED driver sensitive to the dose rate? A: No. LED control gear is tested with the dose rates between 250 and 25.000 Gy/hour without any influence to operation of the Luminaire. Q: Your HiRad series should have “World’s best radiation tolerance in LED lighting”. Is this correct? A: Yes, it is. We specify our products with radiation tolerance of up to 500 KGy. In fact we tested our electronic inside the core of the TRIGA MkII nuclear research reactor to more than 1 MGy (0.1 Grad). And the electronics is still functional. Q: Do you use shielding techniques? A: No, there are no radiation shields inside the Luminaire. Radiation hardness is achieved by design. Q: Are your radiation test reports available to the public? A: All test reports are available to qualified customers. Please address your requests to nuclear@dito-lighting.com.  
HiRad-200PL ® Rad-Hard underwater LED Luminaire
Underwater pool lighting has many small, lightweight but powerfull LED units. Each unit weight about 1 kg. One unit offers more than 5000 lm. System is designed for continuous submersion.
HiRad-50LB ® Rad-Hard Low-Bay LED Luminaire
HiRad-50LB is very light and compact Low-Bay LED Luminaire equipped with opal diffuser  designed for simple one-to-one replacement of the existing 200 W tungsten or standard T8 based fluorescent Luminaires. Recommended mounting height is less than 6 meters.
LED control gear World’s best radiation hardness
World’s best radiation hardness  in LED Lighting, of more than 500 kGy, is a result of carefull selection of the components and the circuit topology. LED control gear is developed and produced by DITO Lighting.  Electronics is based on discrete components without integrated circuits, electrolytic capacitors and optocouplers. LED control gear also demonstrates excellent MTBF of over 3.7 milion hours at 50 o C ambient temperature, using MIL- HDBK-217F Notice 2 calculation method.
LoRad-150HB ® Rad-Hard High-Bay LED Luminaire
LoRad-150HB has the same electrical and optical properties as HiRad-150HB. By using lower grade materials and components this version is much more affordable, with radiation tolerance of up to 10 kGy. LoRad-150HB is designed for less demanding nuclear applications.
HiRad-150HB ® Rad-Hard High-Bay LED Luminaire
HiRad-150HB is a powerfull LED Luminaire, yet very light, compact and easy to install, designed for simple one-to-one replacement of the existing 1 kW tungsten or 500 W HID based Luminaires. It is a High-Bay luminaire designed for mounting heights of over 8 meters.
HiRad-150HB ® Rad-Hard High-Bay LED Luminaire
HiRad-150HB is powerfull, 150 W High- Bay LED Luminaire, delivering more than 17 klm at overall Luminaire efficacy of more than 112 lm/W. HiRad-150HB remains operational at massive gamma doses of over 500 kGy or 50 Mrad, tested inside the core of TRIGA Mk II nuclear research reactor. More…
HiRad-50LB ® Rad-Hard Low-Bay LED Luminaire
HiRad-50LB is scaled-down version of our flagship product HiRad-150HB, sharing the same, proven technology with his older brother. It’s a nuclear grade low-bay LED luminaire, designed to be used in moderate to high radiation areas. Nominal power of 55 W at 5600 lm. More…
HiRad-200PL ® Modular Rad-Hard LED Pool Luminaire
HiRad-200PL is high performance, modular, underwater LED luminaire designed to be used inside the nuclear reactor pool, continuosly submerged. One unit has four underwater 50 W LED lamps on common holder. Total power of the unit is 200 W, with more then 22.000 lm of luminous flux. More…
Minimizing staff exposure HiRad series is designed mainly for high radiation areas especially inside nuclear reactor containment. Beside the radiation hardness, the reliability of the product was of the main concern. Long lifetime and no need for relamping results in lower staff exposure to radiation, according to ALARA radiation safety principle. The Luminaire is fitted with the connector. Skilled technician can replace damaged unit in less than 2 minutes.
When nature strikes One of the most feared natural phenomena in any nuclear facility is the earthquake. Our LED products were tested according to IEEE 344 2013 Seismic Qualification Test for Nuclear Power Plants, surviving and functioning normaly with the base excitation of more than 20 g in any direction in the frequency range between 1 and 40 Hz. Complete HiRad series demonstrates extremly high seismic capacity.  It operates in both OBE and SSE events.
Designed for unthinkable HiRad series is designed for any application where high or even extreme radiation can be expected, allmost independently of the dose rate. HiRad series operates not only under constant steady state irradiation, but can survive also rare event of gamma and neutron burst, caused by unexpected nuclear reactor critical power excursion. It is designed with post-Fukushima requirements in mind and tested for design basis accidents and beyond. All irradiation tests were performed inside the nuclear reactor core with the actual Nuclear Power Plant gamma and neutron spectrum.
Full Nuclear Qualification HiRad series of LED Luminaires is designed  and made from ground up in Slovenia, EU, by DITO Lighting  in cooperation with the Jožef Stefan Institute, Reactor Infrastructure Centre, Ljubljana. Whole HiRad series of LED products has full third party nuclear qualification including: radiation tolerance test seismic capacity test reliability and lifetime prediction calculation safety, environmental and EMC tests complete photometry tests and pressure and chemical compatibilty tests
LoRad-50LB ® Rad-Hard Low-Bay LED Luminaire
LoRad-50LB with radiation tolerance of up to 10 kGy gamma is designed for nuclear applications where lower doses of gamma can be expected. Other optical and electrical characteristics are the same as HiRad-50LB.
Other LED products Heavy duty industrial Luminaires
Extreme 3  HD Series  is a line of high performance Heavy Duty LED lighting products, designed for demanding industrial applications. It includes heavy duty industrial High-Bay lighting and a series of street Lighting Luminaires. More…
LED Pool Lighting Modular underwater lighting
Simple selection of illumination pattern, scalable illumination, simple upgrading, robustness and very easy replacement are main advantages of modular approach. Depending on the nuclear requirements the Luminaire body is machined out of aluminium or copper. Copper is used mainly in NPP’s, aluminium is used in scientific research reactors. Holders are always custom made out of stainless steel. LED control gear is located outside the reactor pool for easy maintenance.
Seismic damper Damping extreme seismic events
Whole HiRad series is equipped with the special seismic dampers. The damper absorbs earthquake schocks and converts seismic energy to the temperature. The damper works well in all three axis in the frequency range from 1 to 40 Hz.
Downloads
HiRad-150HB Leaflet ENG HiRad-50LB Leaflet ENG HiRad-200PL Leaflet ENG
Gamma and neutron hardness Gamma and neutron irradiation tests were performend in the General Dynamics / General Atomic TRIGA Mk II nuclear research reactor in Jožef Stefan Institute, Reactor Infrastructure Centre in Ljubljana, Slovenia. Gamma spectrum of the research reactor mimics real life situation in the NPP much closer then classic irradiation with the 60 Co gamma source. The only choice for neutron irradiation is nuclear research reactor, like TRIGA Mk II. In absence of nuclear standards for Luminaires, military and aerospace standards for irradiation of electronics were used where applicable: MIL-STD- 830, Method 1017 (neutrons) and Method 1019 (gamma) and European Space Agency ESCC No. 2290 for gamma. 
Photometrics Photometric properties of the Luinaries were measured in Europe leading photometric laboratories, using latest photogoniometer instruments. The results of measurements are polar light distribution, color spectral distribution, correlated color temperature and color rendering index. Optical .ldt or .ies files are available on request. All requests should be addressed to nuclear@dito-lighting.com
Reliability and lifetime expectancy The reliability prediction was performed using A.L.D. Ltd. Software “RAM Commander”, in accordance with the MIL-HDBK-217F Notice 2, using Part Stress Analysis method. Environmental condition: GB (Ground Benign).  Mission profile 24/7/365 (continuous operation) at ambient temperature 50 0 C. MTBF values vs. temperature are shown in a graph. Lifetime expectancy at specified mission profile is more than 22 years. Calculation is based on 95% confidence level.
Seismic capacity HiRad-150HB has been tested according to IEEE 344-2013: Standard for Seismic Qualification of Equipment for Nuclear Power Generating Station. IEC 60980: Recommended practices for seismic qualification of electrical equipment of the safety system for nuclear generating stations. Tested by ZAG, Slovenian National Building and Civil Engineering Institute, Laboratory for Building Stuctures and Earthquake Engineering.
EMC Nuclear facilities are packed with precision electronics and high sensitivity sensors, cruicial for proper operation of safety related eqipment. Modern lighting systems are using switching power supplies. Therefore selection of high performance LED lighting is neccessary to prevent interference with other electronics. The result of very careful PCB design of our HiRad series is so called “quiet” design, with extremly low EMC footprint.
HiRad-200PL Leaflet RU HiRad-50LB Leaflet RU HiRad-150HB Leaflet RU
Chemical compatibility and pressure Boric acid is commonly used as neutron absorber. Our HiRad series is tested in the chemical laboratories of Jožef Stefan Institute in Ljubljana for chemical compatibility with common chemicals usualy found in the NPP’s. None of the materials used in Luminaire construction is affected by the chemicals. Overpressure test of the containment is standard procedure in many NPP’s. HiRad series of Luminaires are designed and tested for high ambient pressure of over 7 bar, however due to special pressure equalization system, a much higher ambient pressure can be tolerated. Allowable pressure change is 1.5 bar/h.
Partners DITO Lighting and Jožef Stefan Institute, Reactor Infrastructure Centre, signed longterm agreement of cooperation in development and production of Radiation tolerant LED Luminaires. DITO’s part in the joint venture is development of the electronics, IJS’s role is the expertise in the field of radiation hardness of the mechanical and electronic components used in the final product. The reactor has been playing important role in developing nuclear technology and safety culture in Slovenia. 20 Ph. D. research works, 30 M. Sc. degree works and more than 100 Diploma works have been performed using the reactor. More…
About us DITO is fully privately held company founded in 1992 by Srecko Bizjak B.Sc. (CEO) and Rafael Kitak B.Sc. (R&D). Both are exclusive onwers of the company to this day. In 1995 we developed world’s first multichannel, studio grade, PC based, digital audio recorder DAR-20. In the year 2000 we bring to the telecomunication market our DSP based multichannel, multifunctional, fully programmable, 2 Mbit/E1 digital voice announcement system. In 2007 we developed TNS++, railway copper wire transmission system. TNS++ is still worlds unique product for multichannel DSP based, fully programmable, very high performance tone communication, over standard railway copper wire cables. The system is used for communication between relay based safety related railway equipment worldwide.   In 2009 we started with LED Lighting development. First with the street and heavy duty industrial lighting products. In 2013 we jumped to nuclear LED Lighting bussines. Our goal is to bring to the nuclear market world’s best radiation hardness in the LED Lighting industry.
Postal DITO Lighting Gorica pri Slivnici 144 3263 Gorica pri Slivnici Slovenia, EU VAT: SI59718587 nuclear@dito-lighting.com http://www.dito-lighting.com Sales terms and conditions
Photometry related questions Q: Are your photometric data simulated/calculated or measured? A: Our Luminaire photometric properties are measured in the Europe’s leading laboratories and not just calculated from LED vendor datasheets. Q: What is the output of the photometric measurements in the photometric lab? A: Beside standard test report, the output of the photometry are photometric files used in simulation software. Eulumdat .ldt and IESNA .ies file. Q: Do your Lumen/Watt specification represent LED efficacy? A: No, never. Our efficacy in lm/W is measured in the photometric lab and represent overall Luminaire efficacy - from the wall outlet to the luminous flux out of the product. Q: Your lm/W specification is relatively low in comparison to other LED Lighting vendors. Why? A: Correct. The numbers are lower then most others, because we are not specifying LED efficacy as Luminarie efficacy. There is big difference between this two numbers. LED efficacy is the number taken out of the LEDs manufacturer datasheet, measured in the ideal conditions. Luminaire efficacy takes into account also all photometric and electronic losses, which lovers overall Luminaire efficacy. Optical losses are due to losses in optics, luminaire housing, protective glass or diffuser. The best designs with optics or diffuser have at least 20% of losses. If we add at least 10% of losses in the LED driver, we can estimate overall losses to minimum 30%. In practice this value can be much higher. If Luminarie incorporates high performance LED with 150 lm/W and if we take into equation optical end electronic losses, then overall Luminaire efficacy is less than 105 lm/W. Q: Why should I check which efficacy is specified in the Luminaire datasheet - LED efficacy or Luminaire efficacy? A: Let me explain this with simple example. If we take high performance LED with datasheet efficacy of 150 lm/W and put this LED into the black box, then the overall efficacy of this “Luminaire” will be exactly 0 lm/W. Which datasheet specification for this “Luminaire” is correct 150 lm/W or 0 lm/W? Q: How to avoid wrong and misleading figures in the Luminaire datasheets? A: Simple. Request photometric test report of the Luminaire. Q: Are your photometric test reports available to the public? A: All test reports are available to qualified customers. Please address your requests to nuclear@dito-lighting.com.  
Reliability and lifetime related questions Q: What is MTBF? A: Mean Time Between Failures or MTBF represents the statistical approximation of how long a number of units should operate before a failure can be expected. It is expressed in hours and does not represent how long the unit will last. For instance to test 10.000 units for 1.000 hours with 10 failures, the MTBF value would be 1 million hours. This does not means the unit will operate for 1 million hours or 114 years. With 1 million units operating and MTBF value of 1 million, a failure can be expected every hour. Q: Who performed MTBF calculation for you? A: We contracted our MTBF calculation with Israeli company A.L.D. , the leading consulting firm and software house in the field of Reliability Engineering and Analysis, Safety Analysis and Safety Management, Quality Engineering and Quality Assurance. Q: Which method do A.L.D. use for MTBF calculation? A: There are many methods and standards to choose from for MTBF calculation. We decide to perform MTBF calculation according to US military specification MIL-HDBK-217F Notice 2, one of the most frequently used and recognized standards in the industry. Q: What is the relation between MTBF and lifetime? A: The confusion between these two parameters is the most common confusion in the reliability theory. However, there is some mathematical way to use MTBF to roughly expect a lifetime. For our products the calculated lifetime with 95% of confidence is about 22 years operating 24/7/365 - i.e. continuous operation. Due to exponential nature of mathematical formula, for 100% of confidence the calculated lifetime is zero hours, or with 0% confidence, the lifetime is indefinite. Q: 100.000 hours of lifetime is well known figure for LED lighting. Why are you complicating with calculations? A: 100.000 hours is the number you can find in any LED component datasheet. It is a pure theoretical figure and give us an idea how long a LED component (not a LED Luminarie) can last if it operates under ideal conditions. Conditions inside the LED Luminarie, where the LED component is operating, are far from ideal. The operating temperature (bad thermal design), current density (driving LED at maximum power), the technology and the quality of the LED component are affecting real operating life, which can be much lower then 100.000 hours. Q: Does the LED Luminaire last as long as LEDs? A: Not at all. LED Luminaire has many other components too. The most problematic, and the most unreliable one, is LED control gear, sometimes called LED driver or ballast. By far the most unreliable components in any power electronics, are electrolytic capacitors and optocouplers. Our power supply does not use any of them. Just for comparison. The best electrolytic capacitors have lifetime expectancy of just few thousand hours at rated temperature. Should we expect, that the Luminaire itself will last for 100.000 hours? Probably not. Q: Finally, what is the lifetime of your Luminaire? A: A million dollar question. Statistically speaking, more than 22 years with the confidence level of 95 %. Also statistically, our Luminaire can fail in the first hour of operation or it can last forever. The probability of either is very low, but is possible. Q: Do you use third party LED driver? A: No. We are using only LED driver developed and produced in-house with all required nuclear qualifications.
DITO LIGHTING World’s best radiation hardness in LED Lighting