How does ambient heat affect the light output of LED fixtures?

Ambient heat has a direct and measurable impact on the light output of LED fixtures. The higher the temperature around a fixture, the less light the device produces and the faster the LED chip ages. This effect plays a major role in industrial environments where heat is a constant factor, such as steel mills, foundries, paper production halls, or other environments with intensive heat sources. In this article, we answer the most frequently asked questions about the relationship between temperature and LED performance.

What happens to LED chips at high temperatures?

At high ambient temperatures, the efficiency of an LED chip decreases. The chip produces less light per watt, the color temperature can shift, and the component's lifespan is significantly shortened. This is not a defect, but a physical fact: semiconductors perform less well as they heat up.

What exactly happens is as follows: heat increases the resistance in the semiconductor, causing a greater proportion of the electrical energy to be converted into heat instead of light. This is called thermal saturation. The chip is, in a sense, overloaded not by current, but by temperature.

An additional effect is the accelerated aging of the phosphor layer used in many LED chips to produce white light. At sustained high temperatures, this layer degrades more quickly, leading to color shift and a noticeable decrease in light intensity. In industrial environments where fixtures are continuously running, this is a serious concern.

How much light output does an LED fixture lose through heat?

The light output of an LED fixture can decrease significantly at high ambient temperatures. Depending on the quality of the chip and the thermal design of the fixture, the loss can range from a few percent to more than 30% at extreme heat. This phenomenon is known as LED lumen depreciation.

Manufacturers typically specify the light output of luminaires at an ambient temperature of 25°C. As the actual temperature rises, the actual light output decreases. At a temperature of 50°C, a noticeable difference can already be measured. At 80°C or higher, the loss can become so great that the installation no longer meets the lighting requirements for the workplace.

This is exactly why it is essential in the selection of LED fixtures for warm industrial environments to not only look at the stated wattage, but also at how the fixture performs at the actual ambient temperature at the installation location.

What is the difference between ambient temperature and junction temperature?

Ambient temperature is the air temperature around the fixture. The junction temperature is the temperature at the exact point where the LED chip converts electricity into light, the heart of the chip itself. This distinction is crucial: the junction temperature is always higher than the ambient temperature, and it is precisely the junction temperature that determines how well and for how long an LED performs.

The difference between these two temperatures is determined by the thermal resistance of the fixture. The better the heat is dissipated from the chip to the outside of the fixture, the smaller this difference is. A fixture with poor thermal design can, at an ambient temperature of 40°C, already reach a junction temperature of 100°C or more, with all the consequences that entails.

Therefore, it is important for engineers and project managers to consider the maximum junction temperature (Tj max) and thermal resistance (Rth) when specifying a luminaire. These values provide a more reliable picture of actual performance than just ambient temperature alone.

How does thermal management ensure stable light performance?

Thermal management is the set of measures that allow a luminaire to dissipate heat from the LED chip to the surroundings. Good thermal management keeps the junction temperature low, which directly contributes to stable light output, longer lifespan, and less maintenance. It is one of the most determining factors in the quality of an industrial LED luminaire.

In practice, thermal management consists of a combination of elements:

Heat sinks (heatsinks): Aluminium or other well-conductive materials that quickly dissipate heat from the chip and spread it over a larger surface area.
Thermally conductive compounds: Special pasta or pads between the chip and the cooling body ensure optimal heat transfer without air gaps.
Housing design: The shape and material of the luminaire housing also determine how effectively heat is released into the ambient air.
Active cooling: In extreme cases, fans or liquid cooling are used, although this is less common in industrial fixtures due to their susceptibility to maintenance.
Power regulation: By limiting the current through the LED chip at high temperatures (thermal rollback), overheating is automatically prevented.

A fixture that is well designed in this respect performs stably over a wide temperature range. That is not a luxury in industrial environments, but a basic requirement.

When is a standard LED fixture not suitable for warm environments?

A standard LED fixture is not suitable for warm environments once the actual ambient temperature consistently exceeds the maximum allowable ambient temperature (Ta max) of the fixture. For many consumer fixtures and even some commercial products, this limit is around 35 to 45°C. In industrial environments, this limit is regularly exceeded.

Situations where standard fixtures are insufficient include:

Production areas with ovens, melting furnaces or other heat sources
Steel plants with radiant heat from liquid metal
Dry rooms, paint shops or other heated process rooms
Roofs and outdoor installations in combination with direct sunlight on the fixture
Environments with limited air circulation, which causes heat to accumulate

In such situations, using a standard fixture not only leads to faster lumen depreciation, but also to premature failure of the driver or the LED chip itself. The costs of unplanned downtime and replacement are generally significantly higher in industrial contexts than the initial investment in a suitable fixture.

How do you choose an LED fixture that is resistant to extreme heat?

When choosing an LED fixture for high temperatures, it’s not just about a high IP rating or a robust housing. The thermal specifications of the fixture must match the actual conditions of the installation location. A structured approach helps to make the right choice.

Determine the actual ambient temperature. It measures not only the air temperature, but also the radiation temperature of nearby heat sources and the temperature at the exact installation location of the luminaire.
Check the Ta max of the fixture. Make sure that the maximum allowable ambient temperature of the fixture is well above the measured peak temperature. A margin of at least 10 to 20°C is advisable.
Ask about the lumen output at increased temperatures. Serious manufacturers provide light output curves at different temperatures, so you know what you’ll actually get in the workplace.
Pay attention to the quality of the cooling body. Fluorescent luminaires with a solid aluminum housing and a carefully designed cooling fan design perform better than thin-walled constructions.
Look at the driver specifications. The driver is often the weakest link at high temperatures. Choose fixtures that have thermal protection or can be placed remotely.
Consider specialized fixtures for extreme conditions. For applications above 60 to 80°C, specially developed fixtures for high temperatures necessary, not an average industrial product.

By following these steps, you avoid investing in a fixture that meets the requirements on paper, but that in practice fails months later or significantly reduces its light output.

Practical example: Rockwool Croatia

At the Rockwool factory in Zajci, Croatia, lighting was sought that is resistant to ambient temperatures above 110 °C and to the infrared radiation that is released during the production process. Standard LED lighting, and even many heat-resistant versions, failed under these conditions. At the same time, the LED drivers were not allowed to get warmer than 50 °C, while it was already approaching 40 °C outside in the summer. The lighting design, engineering, installation design, and delivery JEL Products covered over 50 Barracuda HT, over 20 HT, Snapper HT and over 30 Linear HT. The installation achieves more than 100 lux on the work floor.

The temperature around a luminaire determines how warm the LED and the driver become, and therefore how much light remains after a period of time. Those who only look at the air temperature miss the heat that enters as radiation. The thermal design of the luminaires and the driver positioning, designed and tested separately from the hot production areas, were crucial here. This ensures that light output and lifespan remain unchanged, even under extreme thermal stress.

How JEL Products helps with lighting in high-temperature environments

JEL Products It develops and supplies LED luminaires that are specifically designed for environments where ambient heat is a serious factor. The Orca Barracuda high-temperature floodlights are designed for use in steel plants and other environments with extreme heat and infrared radiation, with a temperature resistance of up to +120°C. That is not a marketing claim, but a technical specification that stems from years of collaboration with industrial partners in the toughest sectors.

Specifically, JEL Products offers the following:

Valves with a proven Ta max of up to +120°C, suitable for the most demanding production environments
Technical advice and lighting calculations tailored to the actual temperature conditions of your location
Support in selecting the correct fixture based on junction temperature, lumen output at elevated temperatures, and driver specifications
Complete hassle-free service: from engineering and Custom lighting advice for installation and commissioning
ISO9001 and VCA** certified process, ensuring quality and safety

Do you have a project where heat is a determining factor for your lighting choice? Then please contact us via the JEL Products Contact Page for a free consultation with a technical specialist.

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