When it comes to lighting cold stores and freezers, there are some surprising differences between commonly available light sources. These facilities are used not just for food but also for medicines and other healthcare materials, all of which have different storage needs, so cold stores operate over a range of temperatures. Some are maintained at -5°C but others are at -25°C. Long-term storage can be as low as -40°C. Areas that are kept that cold are normally only lit during access.
The temperature is below zero so these areas are always dry. However, most luminaires designed for cold stores are also fairly well sealed. This simplifies cleaning and ensures that no broken lamps or failed components inside the luminaire can enter the room.
Our example of a cold store is 8 x 6m with a 3m floor-to-ceiling height. Surfaces are clean and with a fairly high reflectance.
EN 12464 recommends 200 lx if the room is continuously occupied. The Code for Lighting recommends 300 lx if there are small items that are difficult to identify. However, 300 lx is also recommended for dispatch, packing and handling areas, so I have designed the three options to this level. For very cold stores, there may be health and safety issues that limit the time staff may work inside.
Both documents recommend a CRI of 60 or more. This is interesting because there are countless store rooms that use standard SON lamps with a CRI below 60. Of course, you can get SON with improved colour rendering of 60–80. ‘White’ SON is even better, but not available in high wattages.
Cold stores vary so much that you should check what colour rendering is required and find out whether people using the store will have to read fine detail such as labels.
The Budget Option
This option uses 70W SON low bays – a common choice for cold stores. These will start from cold down to about -20°C. The warm appearance takes the chill off working although the colour rendering is barely acceptable. We had to use six luminaires here to achieve reasonable uniformity and this means the horizontal illumination of 420 lx is 40 per cent higher than recommended. The vertical illumination of 175 lx is quite acceptable and should enable staff to read labels fairly easily. I wouldn’t use a 150W lamp because it would be too glaring with the 3m-high ceiling. However, the 70W produces fewer lm/W than the 150W, so the overall efficiency is less than might be expected from a high-pressure sodium scheme. Another disadvantage is that there are few low bay luminaires available that can be sealed to a suitable IP rating. Overall, this option is let down by the low lamp efficacy and control gear losses.
Luminaire 70W SON low bay
Optical Hammered aluminium reflector
Arrangement 2 x 3 to achieve uniformity, but it could have been just 2 x 2
Average illuminance at bench level 420 lx
Average vertical illuminance on long wall 175 lx
Luminaire efficacy 47 lm/Wcct
Electrical load 510W
Typical cost for six units £840 including IP-rated cover lens.
Pros Cheap and gives a warm appearance
Cons Not as efficient as you might think, no light on upper walls and ouch, that glare
The T8 Option
This option uses the T8 version of Trilux’s Aragon fitting in a polycarbonate body and produces surprisingly good results. The big advantage of T8 over T5 is that it will operate down to -20°C. It is often forgotten that T5 is normally recommended for +5°C and above. We achieve 340 lx horizontal and a similar level on the walls to the SON. However, the electrical load is almost 20 per cent lower. You get the extra benefit of white light, better colour rendering and no glare. Lamp replacement is cheap and easy because of the fixed, stainless steel clips. Apart from the lower running costs compared with SON, this also has a much lower capital cost. This is a good and effective solution for cold stores.
Luminaire Trilux Aragon with single 58W T8 lamp and polycarbonate body
Optical Specular reflector with prismed polycarbonate cover
Arrangement 2 x 3
Average illuminance at bench level 340 lx
Average vertical illuminance on long wall 177 lx
Luminaire efficacy 68 lm/Wcct
Electrical load 420W
Typical cost for six units £408
Pros Cheap, low running costs, efficient and white light with good colour rendering
Cons Lamps must be changed regularly
The Clear Winner
This is the best of the options. The Nextrema LED has been specifically designed for cold and damp areas. Cold stores are where LEDs show their intrinsic advantages. Their efficacy increases the colder they get, so you achieve 5-10 per cent more light output than at normal room temperature. The horizontal illumination achieved is just slightly more than with T8, but the vertical is over 20 per cent higher and the electrical load remains the same. The opal diffuser also gives a nice glow around the luminaire and on the ceiling. A CRI of over 65 is more than adequate although somewhat less than the T8. It is the coolest of the three options, operating down to -25°C. Of course, the big advantage of the Nextrema LED over the T8 is the long life of the LEDs, and the capital cost is not much more. This luminaire deserves to sell well.
Luminaire Trilux Nextrema 5000K LED with die-cast aluminium body
Optical Opal polycarbonate lens
Arrangement 2 x 3
Average illuminance at bench level 348 lx
Average vertical illuminance on long wall 214 lx
Luminaire efficacy Greater than 73 lm/Wcct
Electrical load 330W
Typical cost for six units £630
Pros Lowest energy consumption, higher illumination than T8 on both horizontal and vertical, good colour, long life and low maintenance
Cons Costs a little more than T8 – but less than the SON option