Lighting Proposal: Replacement of Existing T-8 FL Tube

 

1. Objective

 

To replace existing T-8 (Fluorescent) FL light tubes with more energy saving lights.

 

2. Design Criteria

 

l Achieve one-to-one replacement with minimum alteration to existing light arrangement.

l Maximize energy saving and be as environmental friendly as possible.

l Cost effectiveness.

 

3. Possible Alternatives to Replace the Existing T-8 FL Tubes

 

There are a number of different types of light sources available on the market today, namely incandescent lights, Fluorescent/Compact Fluorescent (CFL) tubes/bulbs, Halogen/Metal Halide lamps and LED (Light Emitting Diode) lights. Upon initial examination, incandescent lights and halogen/metal halide lamps were eliminated for their higher energy consumption and spot lighting characteristics. CFL tubes were also not considered for it incompatibility to fit with the existing T-8 FL light fixtures. In order to switch over to CFL tubes, all the light trays and fixtures would have to be replaced which would mean a substantial increase in capital investment. LED light is a fast developing technology, but is still quite expensive. As a result, LED light is not a feasible option at this moment. The remaining choices for further consideration would be the energy efficient T-5 FL tube.

 

4. T-5 FL Tubes

 

T-8 and T-5 FL tubes on the market today have the typical performance and technical specifications as stated in Table 2 below:

 

Table 1: T-8 vs. T-5 FL Tube Technical Specifications

Lamp Type

 

lumen output/Watt

Wattage

Lumen

T-8

 

75 lumen/w

48 W

3600

T-5

 

90 lumen/w

32 W

2880

 

In terms of energy consumption, a 1200mm T-5 FL tube uses about 33% less energy than a T-8 FL tube, but due to the lower voltage output, a T-5 FL tube would also generate less light than a T-8 FL tube. For example, if a T-8 FL tube is replaced with a T-5 FL tube under a control situation where condition remains the same; there should be a theoretical decrease in brightness of about 20-30%. This calculation could easily be verified on by simply measuring the Lux levels at a specified distance.

 

4.1 Special T-5 FL Tube Converter with Reflector

 

With the addition of the special light enhancing reflector, the normally waste light of about 30% beaming towards the backside of the light tray is reflected back downwards thus becoming useful light again. The total useful light from a T-5 tube beaming downward would effectively be equal to the light from a T-8 light tube. In other word, this combination of T-5 light tube with reflector could achieve the 33% energy saving whilst matching the brightness performance of a T-8 light tube, i.e. one-to-one replacement.

 

By achieving one-to-one replacement, there would be not need to add additional light tubes or trays in order to compensate the decrease in brightness level. Alteration or additional works to the existing lighting arrangement could therefore be minimized.

 

4.2 Cost Savings Analysis

 

The monthly electrical costs of operating T-8 vs. T-5 FL tubes for 11 hours/day are calculated as follows:

 

HK Electric (HK Island)

 

T-8 = (36W + 15W) x 11 hr x 30 days x $1.3/kwh / 1000W = $21.9

T-5 = (28W + 1W) x 11 hr x 30 days x $1.3/kwh /1000W = $12.4

Savings = $ 9.5

 

CLP (Kowloon, N.T. and Outlaying Islands)

 

T-8 = (36W + 15W) x 11 hr x 30 days x $1.0/kwh / 1000W = $16.8

T-5 = (28W + 1W) x 11 hr x 30 days x $1.0/kwh /1000W = $ 9.5

Savings = $ 7.3

 

Assuming a difference of $100 capital cost (cost of converter/reflector unit discounting the cost of the T-5 tube), the calculated return periods are 10.5 months and 13 months respectively.

4.3 Product Warranty

 

The T-5 FL tube converter with reflector unit sold by our company has a factory warranty of 2 years against manufacturer defect, but excluding installation workmanship, normal wear-and-tear, or abuse.

 

4.4 Product and Project Photographs

 

T-5 Converter/Reflector Unit

Installed T-5 Converter/Reflector units at a typical office setting