birding-aus [Top] [All Lists]

## Re: Spotlighting

 To: Re: Spotlighting Andrew Taylor <> Thu, 15 Nov 2001 13:59:13 +1100 (EST)
 On Thu, 15 Nov 2001, Harvey Perkins wrote: > As a very inexperienced sometime-amateur spotlighter, can anyone provide me > with an informative synopsis of the relationship between wattage and > candlepower? Watts are a measure of power. In this case they are measuring electrical consumption by the spotlight. Spotlights used for birding seem to be in the range 10-100 watts. Candlepower are a measure of light intensity. I believe the candlepower quoted for spotlights is for a point in the centre of the beam, i.e. it indicates how bright the centre of the spot will be. Spotlights used for birding seem to be rated in the range 50000-1000000 candlepower. I've not sure how accurate these ratings are. You can't convert watts to candlepower unless you know the efficiency of the bulb, the efficency of the reflector and the shape of the beam. For example, I have a 25 watt spotlight with a narrow beam and a 50 watt spotlight with a wider beam. The centre of the 25 watt spotlight's beam is brighter and it would hence have a higher candlepower rating. The candlepower rating should indicate how well the spotlight will illuminate an object in the centre of the beam at a given distance. The candlepower divided by the distance in metres squared should give you the illumination in lux. At 10 metres a 1000000 candlepower spotlight will illuminate an object in the centre of the beam with 1000000/(10*10) = 10000 lux - similar to a cloudy day. At 100 metres it should be 100 lux - similar to indoor house lighting. At 1 kilometre it should be 1 lux - a little brighter than moonlight. A prescription to avoid harm to fauna by limiting spotlights to 30 watts is vacuous. The limitation should be in lux or perhaps lux hours. For example, other things being equal a 30 watt spotlight will be brighter at 10 metres than a 100 watt spotlight at 20 metres. In other words, you should worry more about distance than watts. My personal opinion, for what little its worth, is that spotlighting has an impact on fauna but the intensity of illumination isn't significant at typical ranges. I doubt the impact from spotlighting is significant, except in locations when spotlighting occurs very frequently. Several years ago, Peter Woodall posted Jack Pettigrew's opinion on this topic: http://menura.cse.unsw.edu.au:1080/1997/04/msg00006.html While I'm rabbiting on, The watts rating should give you a good idea of power consumption. A popular spotlighting power source is 12V 7.2Ah sealed lead acid batteries. These nominally produce 12*7.2 = 86 watt hours. This means a 40 watt spotlight will run nominally for 86/40 = 2 hours. In practice, you'll get less than that depending on discharge rate, temperature, battery age and how well you've treated the battery. As Simon Brock mentioned, you shouldn't discharge sealed lead-acid batteries below about 11.5V. Generally if you notice the spotlight begin to yellow/dim, its time to stop using the battery. Lead-acid batteries have a longer life if kept charged. It also helps if they are stored in a coolish place (< 25 degrees). They self-discharge over period of months. If you are not using your spotlight I presume its better to recharge the battery once or twice a year. If you are transporting sealed lead-acid batteries be very careful to ensure that the terminals can't be shorted - they contain sufficient energy to produce intense heat and start a fire. Covering the terminals with electrical tape is a good precaution. For obvious reasons, you can't transport sealed lead-acid batteries as checked airline luggage. They seem to be theoretically permissable as hand luggage but I suspect you're still likely to be refused permission to carry the size of battery used for spotlighting. Andrew Taylor Birding-Aus is on the Web at www.shc.melb.catholic.edu.au/home/birding/index.html To unsubscribe from this mailing list, send the message "unsubscribe birding-aus" (no quotes, no Subject line) to
 Current Thread Re: Spotlighting, Ian Clayton Re: Spotlighting, Lawrie Conole Re: Spotlighting, Harvey Perkins Re: Spotlighting, Andrew Taylor <= Spotlighting, Neville and Charlotte Brock Spotlighting, Paul Foxworthy Re: Spotlighting, Jeremy Robertson Re: Spotlighting, Bob Forsyth Re: Spotlighting, Reid Re: Spotlighting, Tony Russell spotlighting, michael hunter