Metal halide fixtures are commonly used in high, open ceiling situations. Metal halide fixtures are found in warehouses but some big box stores use them for general lighting.
The oldest fixtures are driven by magnetic ballasts and are referred to as probe start because of the way the process of generating light is initiated. This group of fixtures are typically 400 watt metal halide with a connected load of 455 watts. Newer bulbs with higher output and lower consumption are available to offer modest improvement in operating cost and performance. The group is still plagued by lumen depreciation, poor color rendering and are not a sustainable lighting solution.
Ceramic metal halide lamps greater than 100 watts with pulse start, electronic ballasts are slightly better on all counts but should be reviewed as candidates for retrofit. A lighting audit that defines energy consumption is a major input to the evaluation process. A comparison between metal halide and T5 fluorescent lighting is shown on the table that follows.
T5 High Bay
|Number of Lamps||1||6|
|Fixture Watts (W)||455||351|
|End of Life Lumens||15,750||27,000|
|Rated Lamp Life (hrs.)||20,000||35,000|
|Lumens per Watt||46||81|
|Color Rendering Index||60-70||85|
|Yearly Operating Cost||$168.35||$129.87|
|Strike Time||4 mins.||<1.5 sec.|
|Occupancy Sensor Friendly||No||Yes|
The comparison shows significant differences between these lighting
technologies. Lumen depreciation is a major issue for metal halide
lamps as is color rendering. The strike time, how long it takes the
lamp to get to full output, is significant but the re-strike time is
even longer. Once the lamp reaches full operating temperature (and
output) it must be allowed to cool before re-striking. Even a minor
power fluctuation can trip the ballast causing it to shut down to
protect itself and the lamp. When that happens production and sales are
The retrofit in warehouse and storage areas is typically done with high output, T5 fluorescent fixtures. As can be seen in the table above more light is produced by the fluorescent so replacement is usually on a one-for-one basis where 400 watt HID fixtures are used.
There is an immediate and direct energy savings experienced from the retrofit. There is an opportunity for additional savings if occupancy sensors can be used to turn off fluorescent lamps in unoccupied aisles or areas. Energy savings increase greatly, as high as 70%, if sensors can be used.
The color rendering is much improved with T5 fluorescents and we typically recommend 5000 degrees Kelvin for storage and production areas. There is an argument that says in the world of brown cardboard and gray racks color does not matter. The counter argument is that anytime humans are involved color does matter. Not only does our ability to see color make us more cheerful the presence of blue wave lengths has been found to make us more productive where details are involved.
We have seen examples in Walmart and Office Depot that replaced metal halide lighting with fluorescent fixtures. With no other improvement, replacing one-for-one yields a 30% energy savings. When daylighting or daylight harvesting is used fluorescent fixtures can be dimmed to zero output if adequate daylight is present.
Our recommendation in the sales area is 3500 degrees Kelvin, a neutral color that is neither warm or cool. The 3500K color temperature blends well with halogen accent lighting and is suitable for all price points.
This sustainability action results in lower total cost of ownership. Energy savings is significant and utilities often offer rebates and incentives to lower the investment required. Longer life means lower maintenance cost. The real payoff often comes in increased productivity and sales. Replacing metal halide with fluorescent lighting is the right thing to do 99% of the time.